No luck on my first attempt at acquiring a cesium frequency standard

[hydrogen maser]

So I bought a Datum 4040A Cesium Frequency Standard, just arrived today. I figured given the price (very cheap) that there was a 98% chance that it did not work. And yep, plug it into AC and it immediately starts making that typical failed switch mode power supply noise. I thought great! Hopefully all I have to do is fix the power supply! Getting a device with a failed power supply is often an easy and cheap fix. No such luck. One of the circuit boards has impact damage to it, it is physically broken. There is no damage to the case top so my guess is that what happened was it was opened up for troubleshooting and repair and some idiot dropped something heavy in it and broke that circuit board. Oh well, I knew it was a lottery shot that I would get something this cheap that was fixable, but boy is it disappointing to see something like that. I highly doubt I will be able to find a replacement circuit board.

Edit: SORRY! I just realized that this post is of no use to anyone and it is just me sharing my tale of woe, so does anyone know where I might get parts for a 4040A?

[uncle_bob]

So I bought a Datum 4040A Cesium Frequency Standard, just arrived today. I figured given the price (very cheap) that there was a 98% chance that it did not work. And yep, plug it into AC and it immediately starts making that typical failed switch mode power supply noise. I thought great! Hopefully all I have to do is fix the power supply! Getting a device with a failed power supply is often an easy and cheap fix. No such luck. One of the circuit boards has impact damage to it, it is physically broken. There is no damage to the case top so my guess is that what happened was it was opened up for troubleshooting and repair and some idiot dropped something heavy in it and broke that circuit board. Oh well, I knew it was a lottery shot that I would get something this cheap that was fixable, but boy is it disappointing to see something like that. I highly doubt I will be able to find a replacement circuit board.

Edit: SORRY! I just realized that this post is of no use to anyone and it is just me sharing my tale of woe, so does anyone know where I might get parts for a 4040A?

Hi

I guess the first question would be "how much did you pay?"

The second question would be "can you return it?" (eBay is pretty good about this if it was not properly described).

The most likely case:

You have a unit made up out of the scraps from somebody else repairing a dozen units. Yours is physically complete, but unlikely to work without a lot of effort. Until you get *all* of the various issues sorted out, there is no easy way to check the beam current in the tube.  If the tube is shot, you have a very large paperweight. If the tube is running way low on current, you have a standard that may not be as good as some OCXO's out into the > 10K second region.

You might consider a cheap GPSDO as an option ....

Bob

[hydrogen maser]

No, it is not returnable and not from ebay and I paid very little for it and I knew that it was a total lottery ticket. It does not look like it was pieced together from random parts. The lack of tool marks on all the RF connectors and screws (none missing) and other connectors and the consistent wiring ties and just the general look of a factory job leads me to believe that this is an original unit and not a Frankenstein job. Nothing about it looks like anyone has touched it since the day it was manufactured. The tube seal says 1999 so depending on when it went out of service, is the tube any good now? Who knows. But given the low cost to me I am willing to take a gamble on spending a little to try to fix it or at least have some fun with it.   

[Jay_Diddy_B]

Hi,

May be you can post some pictures?

I have a 5061A that was once of the US Naval Observatory.

Regards,

Jay_Diddy_B

[uncle_bob]

No, it is not returnable and not from ebay and I paid very little for it and I knew that it was a total lottery ticket. It does not look like it was pieced together from random parts. The lack of tool marks on all the RF connectors and screws (none missing) and other connectors and the consistent wiring ties and just the general look of a factory job leads me to believe that this is an original unit and not a Frankenstein job. Nothing about it looks like anyone has touched it since the day it was manufactured. The tube seal says 1999 so depending on when it went out of service, is the tube any good now? Who knows. But given the low cost to me I am willing to take a gamble on spending a little to try to fix it or at least have some fun with it.

Hi

The Datum tubes seem to have about a 10 to 12 year life. Most of these go into service within 6 months of manufacture.

Bob

[wraper]

How complicated is that PCB? Is it multilayer? As for me, I might just glue the pieces together and connect together the broken tracks. As why this damage could happen, IMO it was dropped or received mechanical damage during the shipping. If the board is heavy and flimsy enough, it can break just because of the acceleration shock.

[Macbeth]

1990's PCB is probably double sided, maybe 4 layer at worst. It should be easy to repair with some solder wire bridges etc. if just physical impact damage on some corner of a board. I fixed many a VCR that the wife chucked at the hubby back in the early '90s - when she found him watching blue movies on VHS. The tape would be trapped in the machine of course and we had to return sans such filth. But with a nicely bodged PCB with wire links soldered to scraped off solder mask tracks.

[hydrogen maser]

pics:





Impact damage:

[wraper]

Where is the crack? I only see a conformal coating.

[uncle_bob]

Hi

That's a pretty major crack in the board. It's also pretty un-likely that it's a two layer board. No traces on the top side for a board that heavily loaded .... mulit layer.

Best bet ... hope the cheap deal on this one comes around again.

Bob

[wraper]

Hi

That's a pretty major crack in the board. It's also pretty un-likely that it's a two layer board. No traces on the top side for a board that heavily loaded .... mulit layer.

Best bet ... hope the cheap deal on this one comes around again.

Bob

Still don't see the crack, only the edge where the conformal coating ends.

[hydrogen maser]

Hi

That's a pretty major crack in the board. It's also pretty un-likely that it's a two layer board. No traces on the top side for a board that heavily loaded .... mulit layer.

Best bet ... hope the cheap deal on this one comes around again.

Bob

Yeah, I'm pretty much screwed on this one. Looks like it is a 4 layer board and there is no way I can fix it. Best bet it is look for another one for cheap and hope the parts I need from it match up to mine. Who knows, might even get a good tube from another broken one. Oh well, that is how it goes. Sometimes you win, sometimes you don't.

[uncle_bob]

Hi

That's a pretty major crack in the board. It's also pretty un-likely that it's a two layer board. No traces on the top side for a board that heavily loaded .... mulit layer.

Best bet ... hope the cheap deal on this one comes around again.

Bob

Yeah, I'm pretty much screwed on this one. Looks like it is a 4 layer board and there is no way I can fix it. Best bet it is look for another one for cheap and hope the parts I need from it match up to mine. Who knows, might even get a good tube from another broken one. Oh well, that is how it goes. Sometimes you win, sometimes you don't.

Hi

There still seems to be a bit of confusion between what is damage and what is conformal coating on the board.

Bob

[wraper]

Call me blind but I cannot see the crack.

[hydrogen maser]

Hope this helps point out why I am screwed on this one That is a crack in the board - trust me.

[uncle_bob]

Hope this helps point out why I am screwed on this one That is a crack in the board - trust me.

Hi

Ok, that's how I was interpreting the pictures. Looking at the angle shot, it's very easy to decide that's conformal coat. Since you can see what it is, I'm sure it's apparent that the board is cracked.

Bob

[hydrogen maser]

Sorry if the pic was not clear, my camera sucks. What I outlined in blue is not a shadow edge from a coating or anything else, it is a very nasty crack in the board.

[uncle_bob]

Sorry if the pic was not clear, my camera sucks. What I outlined in blue is not a shadow edge from a coating or anything else, it is a very nasty crack in the board.

Hi

That board has a *lot* of stuff on it.

Have you pulled the board yet? It's not clear if there is something under that board or not.

Bob

[hydrogen maser]

Another angle:

[wraper]

I don't get how the board can be cracked this way, and the most of it, how the crack can match the edge of the conformal coating by 100%. Not a single part is damaged too.

[wraper]

Another angle:

No crack, only conformal coating. If you don't trust me, remove the board and check the other side for the crack being present.

[hydrogen maser]

No crack, only conformal coating. If you don't trust me, remove the board and check the other side for the crack being present.

HA! You are correct! That is not a crack, looked like it to me from many angles until I got the microscope out to look at it. My eyesight is not the same as it was 30 years ago. Thank you! Well, this changes things quite a bit. Back to the PS repair! Always glad to be proven wrong!  

[Fraser]

Hmmmmm, nasty crack but eminently repairable in my experience.

You would need to desolder the components that bridge the crack. Then complete the crack 'circle' with a knife and remove the 'island' complete.

Using a microscope, inspect the edges of the island looking for the tracks. Sometimes the edge needs to be cleaned up with a light sanding. A Dremel multitool may also be used to step down through the layers at the edge of the island. Once all PCB tracks have been identified, the dremel tool is used to reveal them enough for soldering Kynar jumper wires. The same is done to the main PCB so that the Kynar jumpers can straddle the gap between it and the island. It is important to slightly raise the island above the main PCB, like a daughter board to enable the Kynar wires to be soldered around the edges. A support structure will need to be constructed but that is purely a mechanical challenge. Once all wire links are in place, the island may be lowered to within a couple of mm of the main PCB where is needs to be fixed in place using epoxy or some such mechanical fixing method. The jumper wires just sit underneath. The components that stradle the crack will need to be adjusted or modified to fit the slightly elevated island. Wire wrap sockets with their cong legs may be used for chips. Components with longer leads may be required or SMT replaced with through-hole technology.

An alternative approach once the various PCB tracks have been identified is to prepare the island and main PCB edges and attempt to link the tracks using very short lengths of thin tinned copper wire. This can be challenging depending upon the layout of the multi layer tracks.

If the multi layer tracks are too close together at the edge of the PCB, you can use continuity checks to locate their connection points on components. The jumper wire may then be connected to the component leads instead of to the PCB tracks. In some cases this is a far better approach to the problem. You end up with somewhat of a spiders web of Kynar wire, but it works.

This sort of repair is the sort of thing I used to do for the fun of the challenge...... People said the PCB's were beyond repair...... I proved that to not be the case. Some equipment I repaired had been deliberately damaged wiih a hammer blow through the middle of the main PCB. Unrepairable ? No, provided no unique or custom chips had been destroyed. If you really want to wreck kit, you smash up the silicon

I might add that this sort of repair is reserved for non mission critical applications such as data recovery or, as in your case, a desire to bring a unit back from the dead.

Another hint, I used to buy brass tube, rod  and hollow box section from the modelling shop. I used it to create temporary or permanent scaffold for the island PCB The brass solders easily and is pretty rigid. I used the brass to reinforce the epoxy joining of the PCBs by so,dering to the ground plane copper. I never had a repair fail and the PCB strength was maintained.

One for a rainy day maybe ?

Fraser

[Fraser]

Having just looked up the Burr Brown PCM54 chip, I see that it is just a Digital to Analogue converter, and the MC6821 is the very common PIA that many MC6800 series processors used.
The data sheets for the two chips will give you some idea of the connectivity and may help identify what is likely connected to other parts of the PCB, such as the address and data lines. They may be jumper end to other chips that  need the same, or nearby buffer chips that serve them, such as the common 74LS245.

Fraser

[Vgkid]

Best of luck, what ocxo does it have inside of it(should be decent).

[edpalmer42]

I have his big brother, the 4065A.  The main board looks identical to yours.  It also has the internal cesium unit model #5045A including the strange conformal coating over part of the board.  You can see pictures of mine here:

http://s701.photobucket.com/user/edpalmer42/media/Datum%20FTS-4065A/SAM_0322_zps0r3j6ssc.jpg.html?sort=4&o=0

But before you get too involved, I have two things to tell you about.

First, a cesium standard has a limited lifetime.  Whenever it's on, it's using up its supply of cesium.  Once that's gone, the cesium tube is a paperweight and the entire unit is a boat anchor.  So, if you've got the equipment, you should test the tube.  I've attached the test results from my tube.

Second, on the main board, look at U51.  It's in a PLCC44 package.  It's an STEL-1173 NCO (Numerically Controlled Oscillator).  This chip almost always fails with age.  Since it's a obsolete, specialized chip with no second source, it's hard to find.  I got mine a couple of years ago from here:

http://www.aliexpress.com/item/Free-shipping-10PCS-STEL-1173-CM-PLCC/2023682701.html

I chopped out the old chip and soldered in a socket so I can replace it easily if necessary.

Actually, the chip failure could be a good thing.  Hopefully, the chip failed before the tube ran out of cesium.  That's what happened with mine.  There's no way to tell how much cesium is left, but mine is working okay for now.

So, if the power supply repairs look reasonable, go for it.  It'll make the other tests a lot easier.  If not, maybe you could remove the failed power supply and substitute external supplies as necessary.

Let me know if (when!) you have more questions.

Ed

[hydrogen maser]

Just so everyone is clear on who is the idiot in this situation, that would be me. I apologize for not recognizing my failing eyesight. I often rely on cameras and lenses to help me see things as I am far from being young anymore. The "crack" in the board is no such thing. There is a conformal coating on the board that in some small defense of my stupidity I would note that it is slightly odd and nothing like anything I have seen before, just a single small spot on a large board. edpalmer42, thank you for your information and advice. 

[hydrogen maser]

Looks like I am at a dead end on this one for now. The main switch mode power supply appears to be working ok, it looks like something is wrong with the high voltage power supply in the 5045A. The unit won't go into the initialization routine when it is brought out of storage mode. At 2KV DC, I don't have the equipment or courage to troubleshoot it. Not worth messing around with that kind of voltage. There is also evidence that someone else has been in there because the RF connector for the 10mhz oscillator was disconnected and one of the mounting brackets for the tube assembly was crooked.

[Fraser]

You are a very honest person for admitting your error in misidentifying a crack. Respect to you sir.

Regarding eyes.... I am 48 and must use magnifying devices when working on electronics. It has taken me quite some time to come to terms with my eyes ageing. They used to be 20:20 with excellent near vision. Now I find I need to hold items at arms length, or wear my glasses.

Fraser

[uncle_bob]

Looks like I am at a dead end on this one for now. The main switch mode power supply appears to be working ok, it looks like something is wrong with the high voltage power supply in the 5045A. The unit won't go into the initialization routine when it is brought out of storage mode. At 2KV DC, I don't have the equipment or courage to troubleshoot it. Not worth messing around with that kind of voltage. There is also evidence that someone else has been in there because the RF connector for the 10mhz oscillator was disconnected and one of the mounting brackets for the tube assembly was crooked.

Hi

... so back to the "maybe a kit of parts" theory.

Bob

[edpalmer42]

Do you have the manual and have you hooked a computer to the RS-232 port?  Do you have the old DOS monitor program?  What responses are you getting?

In case you know this, I'm playing to the audience!  When you power up a cesium standard that's been sitting around for a long time, it won't start right away.  A Cesium tube requires a really hard vacuum so the first thing it does is pump down the tube to an acceptable value using an ion pump.  This could take a day or more - even a week or more, depending on the state of the tube.  The ion pump runs in storage mode, but you have to turn the unit on to query it.  There's also a monitor point on my ion pump power supply that gives 1mv=1ua.  You could measure this in storage mode.

Ed

[edpalmer42]

Here's some info to get you started.  The manual is for the 4040B.  There might be a few changes, but the majority will be good.

The monitor program runs under DOS.  It might run in a VM.  It's kind of a dopey program so you might want to just hook a computer to the RS-232 port and use the info in the manual to type the command strings through a terminal program.  I've done both.  Your call.

To monitor the ion pump, look at the two high voltage supplies.  Remember that you can do this in either storage or operate mode.  One supply has three low-voltage terminals on the side.  Power, ground, and monitor.  Measure the voltage between ground and monitor.  You should see a negative voltage of a few hundred millivolts or less.  What do you see?

Oops!  Turns out you can't attach a file greater than 1 Meg.  I've uploaded the manual to Mediafire.  Help yourself.

http://www.mediafire.com/download/6icdc7v35c68t16/4040B_mnl.pdf

Ed

[hydrogen maser]

Thank you edpalmer42! That helps a lot. This is a very strange device with some odd operational behavior. Now that I have a manual it makes more sense. Of course in my box of old serial port cables and gender changers I have everything except the the parts I need so I ordered the right cable, should be here early next week. From reading the manual it still looks like something is wrong because it should have gone into initialization mode regardless of how long it had been unplugged, but it does not. Of course, I have been wrong about everything about this device from day one so who knows what is going on with it. Once I have the right cable I will be able to see what (if anything) comes out of the serial port and that will tell me something. The disconnected oscillator cable was odd, but it might not have been human hands that did that. It has no tool marks on it and it fits loosely (unlike the nice tight fit of the other RF connectors), is on the bottom of the module, and has other RF cables that push against it. Might just be one of those things. I don't know. I thought it would be fun to play with this thing even if it did not work and I could at least take the 10mhz oscillator out of it for something else, but it has been more of a challenge than I thought it would be. It is very odd in a lot of ways, but in for a penny, in for a pound.

[guido]

Having just looked up the Burr Brown PCM54 chip, I see that it is just a Digital to Analogue converter, ....

Fraser

Yes a 16 bit stereo DAC for audio purposes. But not 'just' a DAC as this one has parallel inputs (same for the 55, anything else is serial). Hard to get if you need one and i did, as it is used in a calibration jig for an Iwatsu scope.

[Vgkid]

I figured if the tube was shot, it should contain a pretty decent 10Mhz ocxo.

[hydrogen maser]

Vgkid, yeah, obviously it has a 10mhz ovenized oscillator, don't know who made it as it is marked with a Datum part number and label. I assume it must be pretty decent tough.

[edpalmer42]

I figured if the tube was shot, it should contain a pretty decent 10Mhz ocxo.

The OCXO appears to be either a clone or an OEM version of the HP 10811.  Some other Cesium standards from FTS/Datum included a much fancier OCXO like the Datum 1000B in the FTS-4060.  Would love to find one of those.  Of course, since I'm a cheap S.O.B., that's not going to happen. 

Ed

[edpalmer42]

Thank you edpalmer42! That helps a lot. This is a very strange device with some odd operational behavior. Now that I have a manual it makes more sense. Of course in my box of old serial port cables and gender changers I have everything except the the parts I need so I ordered the right cable, should be here early next week. From reading the manual it still looks like something is wrong because it should have gone into initialization mode regardless of how long it had been unplugged, but it does not. Of course, I have been wrong about everything about this device from day one so who knows what is going on with it. Once I have the right cable I will be able to see what (if anything) comes out of the serial port and that will tell me something. The disconnected oscillator cable was odd, but it might not have been human hands that did that. It has no tool marks on it and it fits loosely (unlike the nice tight fit of the other RF connectors), is on the bottom of the module, and has other RF cables that push against it. Might just be one of those things.

Which, what, who?!!  Disconnected cables?!  You didn't say anything about that.  Loose fit?  Shouldn't be!  It's a standard SMA that should be tight enough that you need a small wrench to undo it.  Anything else that you haven't mentioned?

You haven't given us a picture of the bottom of the unit that has all the RF and Cesium parts.  Maybe you should do that.

Have you had time to make the measurement on the ion pump monitor?

Ed

[hydrogen maser]

Which, what, who?!!  Disconnected cables?!  You didn't say anything about that.  Loose fit?  Shouldn't be!  It's a standard SMA that should be tight enough that you need a small wrench to undo it.  Anything else that you haven't mentioned?

You haven't given us a picture of the bottom of the unit that has all the RF and Cesium parts.  Maybe you should do that.

Have you had time to make the measurement on the ion pump monitor?

Ed

Actually, I did mention that one of the RF connectors was disconnected, it was P51 in the image below (not screw on - a snap on-press fit connector): 



Full view of the bottom of the 5045A unit (mine does not look like the older ones I have seen on the web):

[uncle_bob]

Thank you edpalmer42! That helps a lot. This is a very strange device with some odd operational behavior. Now that I have a manual it makes more sense. Of course in my box of old serial port cables and gender changers I have everything except the the parts I need so I ordered the right cable, should be here early next week. From reading the manual it still looks like something is wrong because it should have gone into initialization mode regardless of how long it had been unplugged, but it does not. Of course, I have been wrong about everything about this device from day one so who knows what is going on with it. Once I have the right cable I will be able to see what (if anything) comes out of the serial port and that will tell me something. The disconnected oscillator cable was odd, but it might not have been human hands that did that. It has no tool marks on it and it fits loosely (unlike the nice tight fit of the other RF connectors), is on the bottom of the module, and has other RF cables that push against it. Might just be one of those things.

Which, what, who?!!  Disconnected cables?!  You didn't say anything about that.  Loose fit?  Shouldn't be!  It's a standard SMA that should be tight enough that you need a small wrench to undo it.  Anything else that you haven't mentioned?

You haven't given us a picture of the bottom of the unit that has all the RF and Cesium parts.  Maybe you should do that.

Have you had time to make the measurement on the ion pump monitor?

Ed

Hi

..... kit of parts .....Somebody tossed a bunch of "almost right" stuff together. You get a clone 10811 with a SMB connector and an SMA cable hanging loose.

Yes pictures / part labels / mounting locations would help sort things out a bit. Without that, the best guess is that this is a Frankenstein.

Bob

[hydrogen maser]

Not seeing what looks non-factory or wrong about it. Nothing looks like it was pieced together. Please point out exactly what looks wrong about it so I can understand your point because I don't get it.

[uncle_bob]

Not seeing what looks non-factory or wrong about it. Nothing looks like it was pieced together. Please point out exactly what looks wrong about it so I can understand your point because I don't get it.

Hi

Well, the pictures posted as my post was going up. The forum is a bit "interesting" in that respect. I just rejected this post as being "to soon". Since none of us know where the gizmo came from or anything like that, the only thing we can do is make random guesses.

Bob

[hydrogen maser]

I have been wrong about almost everything about this device but the one thing that I am most sure about is that there is no evidence that I have seen that this is anything but an original factory unit. I have been wrong about lots of stuff, this is a very strange beast, so take that for what it is worth (if anything), I am far from perfect. I have seen zero evidence anywhere inside this device that anyone has touched it since it was manufactured. My guess is that this particular era and revision of this very obscure device has just not ever been documented on the web yet. There is a first time for everything.

[edpalmer42]

Thanks for the picture.  Everything looks good.  I was worried that there might have been a missing module or something.  Yours has a different model of Cesium tube, but everything else looks pretty much identical to mine.

I had to go look at mine, but you are correct, it's an push-on SMB connector rather than a screw-on SMA.  Just goes to show the danger of relying on memory!  My apologies.  But you said that your connector is loose.  Mine has a nice 'snap' going on and requires a bit of effort to pull off.  Maybe do a close visual inspection on the inside of both ends.  There is another SMB connector nearby.  It's over toward the high voltage supplies.  Use that for comparison.

Bob, I don't see anything to suggest that this is a 'Frankenstein'.  If you compare HM's pictures to mine, the units look like twins as far as the Cesium/Main Board unit is concerned.  Makes sense since they're the same model number.  The basic module is 5045A.  Wrap different power supplies and user interfaces around it and you've got either HM's 4040A or my 4065A.  Yes, I know that Frankensteins happen, but only when you've got a bunch of identical units.  Who has a bunch of Cesium standards?? 

Ed

[uncle_bob]

Thanks for the picture.  Everything looks good.  I was worried that there might have been a missing module or something.  Yours has a different model of Cesium tube, but everything else looks pretty much identical to mine.

I had to go look at mine, but you are correct, it's an push-on SMB connector rather than a screw-on SMA.  Just goes to show the danger of relying on memory!  My apologies.  But you said that your connector is loose.  Mine has a nice 'snap' going on and requires a bit of effort to pull off.  Maybe do a close visual inspection on the inside of both ends.  There is another SMB connector nearby.  It's over toward the high voltage supplies.  Use that for comparison.

Bob, I don't see anything to suggest that this is a 'Frankenstein'.  If you compare HM's pictures to mine, the units look like twins as far as the Cesium/Main Board unit is concerned.  Makes sense since they're the same model number.  The basic module is 5045A.  Wrap different power supplies and user interfaces around it and you've got either HM's 4040A or my 4065A.  Yes, I know that Frankensteins happen, but only when you've got a bunch of identical units.  Who has a bunch of Cesium standards?? 

Ed

Hi

Well I can answer the last part of that:

These Cesium standards were sold in bulk to the telecom guys. They went into central office locations rather than into labs. Those guys never bought "just one". (No, that's not a guess, it's first hand knowledge). The fleet was deployed out around the country and the units went back to a depot to be maintained. The depot did the normal modern approach to fixing anything. They swapped out parts to get it working. As parts got scarce, they swapped parts between units to get ones working. The last unit on the shelf still had a full set of parts in it. Since these are high dollar items, you don't take them apart with a crowbar. Somebody tries really hard even on that last unit to get it running before giving up on it.

It doesn't have to look like a Frankenstein to be one. All it has to be is the parts donor that fixed the other dozen they had to repair.

Bob

[hydrogen maser]

I looked at the connector and cable end for P51 and they do not appear to be damaged. They look ok. Perhaps "loose" was the wrong word to describe it. How about "not super tight like all the other ones"? I could see given its position on the bottom of the unit (upside down) and with other cables that press on it how it could pop off in shipping. Not going to have a lot of time right now to play with this unit because I have a big work project going on this week. I am going to wait for the serial cable to arrive and then see what it shows (if anything). 

[edpalmer42]

Hi

Well I can answer the last part of that:

These Cesium standards were sold in bulk to the telecom guys. They went into central office locations rather than into labs. Those guys never bought "just one". (No, that's not a guess, it's first hand knowledge). The fleet was deployed out around the country and the units went back to a depot to be maintained. The depot did the normal modern approach to fixing anything. They swapped out parts to get it working. As parts got scarce, they swapped parts between units to get ones working. The last unit on the shelf still had a full set of parts in it. Since these are high dollar items, you don't take them apart with a crowbar. Somebody tries really hard even on that last unit to get it running before giving up on it.

It doesn't have to look like a Frankenstein to be one. All it has to be is the parts donor that fixed the other dozen they had to repair.

Bob

Which telcos did that?  You said 'deployed out around the country'.  Was that AT&T back in the day?  The reason I ask is that I worked in the Network Standards department of a Canadian Telco.  We had one of the twelve Class-1 Regional Switches in North America.  I don't know if that still means anything.  We certainly had Cesium Standards for synchronizing the digital network and operating in plesiochronous mode (geez I struggled with that word - now I can't forget it ) with other networks, but they were 48V powered, Central Office equipment.  I was very familiar with our labs and they had no lab-style Cesium Standards.  I think that was when I was first bit by the Time-Nuts bug although the term didn't exist back then.

Ed

[uncle_bob]

Hi

Well I can answer the last part of that:

These Cesium standards were sold in bulk to the telecom guys. They went into central office locations rather than into labs. Those guys never bought "just one". (No, that's not a guess, it's first hand knowledge). The fleet was deployed out around the country and the units went back to a depot to be maintained. The depot did the normal modern approach to fixing anything. They swapped out parts to get it working. As parts got scarce, they swapped parts between units to get ones working. The last unit on the shelf still had a full set of parts in it. Since these are high dollar items, you don't take them apart with a crowbar. Somebody tries really hard even on that last unit to get it running before giving up on it.

It doesn't have to look like a Frankenstein to be one. All it has to be is the parts donor that fixed the other dozen they had to repair.

Bob

Which telcos did that? 
Ed

Hi

My view of this is from the "supplier" end rather than the "user" end of things. At one point my boss was the head of FTS. Beyond that, I'd really rather not get into.

Pretty much all of them. You see Datum cesium's with KS numbers on them, you see them with Sprint tags, you see them with Verizon tags. That's just the ones I recognize. The whole "islands of sync" thing based on an autonomous local standard and interpolation at a large number of network edges is what seems to have driven it. HP went after the lab and military applications, but pretty much ignored the telecom's. Dataum / FTS saw that there was a very real market for network sync. That's what made them an attractive acquisition target for Symmetricom. 

Back in the day, AT&T was able to get away with a much more "top down" sort of approach. They were the only guys in town and they could propagate sync from a fairly narrow base of master standards. Once it all broke up, you had a bunch of "little Bell's" all that needed their own sync setup. Next along came the cellular guys and their needs for sync. Pile the explosion in network based telephony (and a bunch of people nobody has heard of hauling it) you have another empire of sync. Net result ... you need more master clocks.

Bob

[wkb]

Do the Rb standards used by telcos/cell operators fit in this same story somehow?  Cs being of a higher standard than Rb references obviously.

[edpalmer42]

Do the Rb standards used by telcos/cell operators fit in this same story somehow?  Cs being of a higher standard than Rb references obviously.

Yes and no.  Rb standards don't have an inherent end-of-life mechanism like Cs standards do.  An Rb standard could run for 20 years continuously.  But Rb standards do age while Cs standards don't.  So depending on your application, you might have to occasionally nudge a Rb standard to bring it back on frequency.  Typical aging rates for Rb are in the range of 5e-11 per month.  That's what they put in the spec sheets - YMMV.  It's not unusual to find a Rb standard that does much better than spec.  Cs standards are specified as having a maximum error as low as 1e-12 for life.

Ed

[uncle_bob]

Do the Rb standards used by telcos/cell operators fit in this same story somehow?  Cs being of a higher standard than Rb references obviously.

Hi

Back in the "good old days" you had "Stratum" levels for timing. Things have changed a bit, but the ideas still apply. The "master source" needs to be a primary standard. It is intrinsically on frequency / on time. That makes cesium a real good candidate for Stratum one. The next layer down is a standard that mostly locks up to the higher level. If something bad happens, it is required to run for a long time without locking up to the higher level. That's where Rb's come in. They have the stability to do this "holdover" process.

The next level down was Stratum 3. That was an OCXO based approach with less holdover time. The idea was that the further you got from the "center" the less the impact of a fault. The other assumption was that the fault was something you could get to and fix a lot quicker.

After a bit of time went by, you got things that crossed between the various levels. You got 3E and all sorts of other levels that never really existed in the original approach. Fast forward a decade or so and you have stuff that does not fit in any category. Most of these cesium standards went into those sort of systems.

Bob

[jwm_]

I think it is more that the availability of relatively cheap GPS recievers and ubiquitous free NTP servers short circuited most of the strata allowing anyone to get a stratum 2 clock on a relatively inexpensive budget if needed and an okay distributed clock with just IP if that is all you need. strata between the two don't make as much sense.

this app note does a fairly good job explaining the statum levels and their accuracy requirements
http://www.raltron.com/products/pdfspecs/sync_an02-stratumleveldefined.pdf

[uncle_bob]

I think it is more that the availability of relatively cheap GPS recievers and ubiquitous free NTP servers short circuited most of the strata allowing anyone to get a stratum 2 clock on a relatively inexpensive budget if needed and an okay distributed clock with just IP if that is all you need. strata between the two don't make as much sense.

this app note does a fairly good job explaining the statum levels and their accuracy requirements
http://www.raltron.com/products/pdfspecs/sync_an02-stratumleveldefined.pdf

Hi

Once the network guys started in with the Stratum numbers, a lot of others copied the same terms without using the same limits. An NTP server that runs as stratum 1,2,3 is massively less accurate than it's network counterpart with the same name.

Bob

[hydrogen maser]

So I got the right cable (I think) but am not having any luck running the monitor.exe program. I'm on Win 7 Pro 64bit so I have to use an emulator - tried dosdox but not getting anything to work. I just says alarm 52. Alarm 52 is not in the manual and I think that just means the program can't communicate with the unit. Not too surprising given all the weird virtual emulator + usb to serial cable, etc.. Now trying direct terminal programs, but putty won't send the right control characters (02 and 03) that I need to format the messages. Arg... trying some other terminal programs, maybe one will work.

[edpalmer42]

How far back does your DOS experience go?  In general, you can send any character by holding down the ALT key and use the number pad to type in the decimal ASCII code for the character.

e.g. <ALT down>65<ALT release> sends capital 'A'.

I just triied it in putty and the Windows 10 DOS window.  Seems to work.

The other thing to do is create the two or three command strings however you can and then try a copy/paste.  If you want to do any data logging, you should write a little program to send the strings and log the results.

Ed

[hydrogen maser]

I'm not going to bother trying anymore with the serial port, I can't get it to do anything. My guess is that the CPU is not starting up/working because it never goes into initialization mode and won't respond to the serial port, the only thing that comes out of the serial port is a series of 5 nulls (00) - not a good sign. The 10mhz/5mhz/1mhz outputs are all working and read bang on what they should be and the waveforms look like they should on the oscilloscope (granted my test equipment is nowhere near what is needed to measure this device) so at least the oscillator is working and that signal is making it to those outputs. The .1/1/5/10 and 1 PPS outputs don't work - they just show noise across the entire spectrum from near dc up to about 90 mhz. 

edpalmer42 - you think the below should be my next step on this one?
To monitor the ion pump, look at the two high voltage supplies.  Remember that you can do this in either storage or operate mode.  One supply has three low-voltage terminals on the side.  Power, ground, and monitor.  Measure the voltage between ground and monitor.  You should see a negative voltage of a few hundred millivolts or less.  What do you see?

[edpalmer42]

I'm not going to bother trying anymore with the serial port, I can't get it to do anything. My guess is that the CPU is not starting up/working because it never goes into initialization mode and won't respond to the serial port, the only thing that comes out of the serial port is a series of 5 nulls (00) - not a good sign. The 10mhz/5mhz/1mhz outputs are all working and read bang on what they should be and the waveforms look like they should on the oscilloscope (granted my test equipment is nowhere near what is needed to measure this device) so at least the oscillator is working and that signal is making it to those outputs. The .1/1/5/10 and 1 PPS outputs don't work - they just show noise across the entire spectrum from near dc up to about 90 mhz. 

edpalmer42 - you think the below should be my next step on this one?
To monitor the ion pump, look at the two high voltage supplies.  Remember that you can do this in either storage or operate mode.  One supply has three low-voltage terminals on the side.  Power, ground, and monitor.  Measure the voltage between ground and monitor.  You should see a negative voltage of a few hundred millivolts or less.  What do you see?

If the processor isn't working, who output 5 nulls?  Remember our manual is for the 4040B.  Check the comm parameters.  Start by scoping the data xmit line from the unit to check the baud rate and look for repeating bursts of data.  You can also 'scope around and see if there's activity on the dataand address lines in and out of the processor.  Also, if you haven't already done so, check power supplies for level and noise and nudge all socketed chips out and back in.  For now, limit things to the main board.

If the processor isn't working, then almost nothing is working.  Yes, the oscillator feeds directly to the divider that generates the 10/5/1 MHz output, but the oscillator is just free-running.  The processor doesn't just monitor and talk to the outside world, it runs the entire process.  When you say the frequencies are bang on, how are you measuring them.  Do you have a GPSDO?

Yes, you should measure the ion pump.  That won't tell you if the tube is healthy, but it's a necessary step before you can do much else that involves the tube.

Ed

[edpalmer42]

I realized that my unit is overdue for a run so I'm going to try to duplicate what you're doing.  Since my unit is basically the same 5045A Cesium module that you have with a fancier user interface, I'll disconnect my user interface and talk directly to the 5045A.  I think that should duplicate what you've got.

First, a correction.  Turns out that the ion pump power supply has 4 terminals rather than 3 like I said.  Mine is labelled as +24, GND, I PUMP, and FAIL SENSE.  Measure the voltage between I PUMP and GND.

I'm just getting ready to start measuring my ion pump.  My unit has been unplugged for 10 months so it should be interesting.  I'll capture the voltage data and post the graph.

Ed

[edpalmer42]

Okay, good news and bad news.  Turns out my unit had an unnoticed fault.  The ion pump won't run in storage mode.  I'll have to investigate that later.  But when I turned it to operate mode, everything was fine.

The attached graph needs some explaining.  The trash at the beginning was before the unit was plugged in.  Then I waited for the ion pump to kick in.  Nothing.  Wiggled the leads and caused that first downward spike at about 22:27.  Damn, it's not working!  Checked my old notes and realized that the same thing happened the last time I did this measurement.  Powered down the unit and rearranged my leads.  That's the 'thin' section.  Powered up again and turned the power to operate.  Waited a few minutes while it did some "pre-flight checks".  Finally the ion pump kicked in and went to ~ -0.09 volts.  This equals about 90 ua of ion pump current.  Pretty good for 10 months on the shelf considering that the supply can source up to 300 ua.  I was making about 4 measurements per second so I'm confident in this measurement.  Over the next 10 minutes it faded down to about -0.005 volts which is where it always sits.  The unit reports the ion pump current as 000.  This test is actually better than my previous one.  After being shut down for only 6 months, the ion pump spiked to 140 ua.

It's getting late.  Tomorrow I'll start on the comm link.

Ed

[edpalmer42]

First phase of the comm challenge.

I connected directly to the 5045A module using a three-wire connection to a USB/serial converter and putty.  Not the results I expected.  I tried 2400 7o2 as stated in the 4040B manual, but the results were gibberish.  But there were results spit out automatically every second.  Changed to 4800 7o2 and saw the following repeated endlessly:

Code: [Select]

XR05-005|RR +0004|Z*-$$$|RZ*-0092Y

XR05+015|RR -0014|Z*-024|RZ -0011Y
^                                ^
|                                |
ASCII 01                         ASCII 17
The capital 'X' and 'Y' are standing in for the control codes.  The first line was before lock, the second line was after lock.

I tried to talk to the unit, but it ignored me.  Since this protocol doesn't match what we're expecting, I'm going to move on.

HM, does the 4040A have another processor board between the 5045A and the comm port?  I'm going to move my connection from the 5045A to the main comm port on the back.  That'll be in the next message.

Ed

[hydrogen maser]

edpalmer42 thanks so much for all the time and effort you have put into helping me, I really appreciate it. I pulled a "real" serial port card out of a different computer. Going to try connecting through that and see if I see anything - I will also try different baud rates. As to the oscillator "working",  all I know is that my frequency counters and oscilloscope say it is exactly what it should be, but they are not really up to the task of measuring something like this. So the oscillator is not grossly broken. I'm guessing it is just free running and not locked to the cesium. If I don't get anything from the serial port on the computer I will see if anything is on the tx line with the scope, I have the rs232 trigger and decoder options in my scope so that is helpful. I will also measure the ion pump.

[edpalmer42]

One suggestion.  When you run this unit, keep it horizontal.  Some time ago, I was running it while it was standing on its side.  I had a couple of instances where the unit lost lock.  I was logging the data at the time and some of the parameters were very odd.  I put it flat on the bench and things smoothed out.  No problems since.  I don't know if it's supposed to be position sensitive - the manual doesn't mention it - but I decided that from then on, I'd only run it horizontal.

By the way, does your unit have anything on the back about options?  Since your Cesium tube is different from mine, I was wondering if you got the high performance tube.  Cross your fingers and hope you didn't.  The high performance tube lives fast and dies young!

Ed

[hydrogen maser]

Nothing on the back about any options and no extra telco options boards installed. The serial port on the 5045A is completely dead. I finally did what I should have done to begin with and unplugged the serial cable from the 5045 that went to the connector on the case and probed the pins directly on the board. Nothing. It is really a shame that there is no service manual for this thing because there are a dozen test points just on the top board. Measuring some voltages at various places now. 

[edpalmer42]

So it's just wires from the 5045A to the back panel?  Odd.  Mine goes to the processor board for the front panel.  By the way, I checked the firmware on my main board.  You and I have identical versions so we should see the same data.

I see that U3 and U5 in the corner of the main board near the RS-232 connector are a 1488 and 1489.  Can't get much more 'old school' than that!

As for the service manual, I guess that companies that buy this kind of unit don't mind paying for repairs.  Rather than have their own techs muck about with it, they'd rather pay the bucks to ensure that the unit is in perfect condition.  I suspect that repairs to something like this weren't cheap - no matter how simple the fix.

Ed

[uncle_bob]

So it's just wires from the 5045A to the back panel?  Odd.  Mine goes to the processor board for the front panel.  By the way, I checked the firmware on my main board.  You and I have identical versions so we should see the same data.

I see that U3 and U5 in the corner of the main board near the RS-232 connector are a 1488 and 1489.  Can't get much more 'old school' than that!

As for the service manual, I guess that companies that buy this kind of unit don't mind paying for repairs.  Rather than have their own techs muck about with it, they'd rather pay the bucks to ensure that the unit is in perfect condition.  I suspect that repairs to something like this weren't cheap - no matter how simple the fix.

Ed

Hi

Equally likely:

The service manual has stuff in it that a competitor might be interested in. That's what killed off schematics of test gear in general. Now if you want the manual, you must have a "need to know". Next step is to get approved ( = yes you buy a lot of them).  Then your boss's boss signs the NDA and the manual gets sent over.

Bob

[edpalmer42]

Oh, I hate serial ports soooooooooooooooo much. 

Fighting with the leads, straight through, swapped, CTS/RTS, friggin' non-standard standard, crap!  Turns out the serial/USB converter I was using was FUBAR.  Anyway, from the port on the back of my box, 9600 7o2, using putty to send the D*1 and D*2 commands, here's the output.

Code: [Select]

=~=~=~=~=~=~=~=~=~=~=~= PuTTY log 2016.03.16 20:39:32 =~=~=~=~=~=~=~=~=~=~=~=
X
ID00000 XXX XXhXXmnXXs 2 R+Z ALM:01(16,00,00,00,00)C+000 F+000000 +25.35V Ct05.0
R-047RR +0043Z+012RZ -0060AR+5029PR0037AZ-4417PZ0062A0-0002GN*5.00LA+0007Pu-4499
+5.08V T+31.8 +14.9V -15.3V OLc FO14.4 VS17.5 VF0.75 IC15.3 HT09.0 IP000 +020 mV
00:00:00 00:00:00 O O O O O AC  33.3 00:00:00 00:00:00 M2m0 Y SYS:0000
XX
ID00000 XXX XXhXXmnXX Vs 17.5V Vf 0.75V GDAC 002 -15:+00 +15:+00 +45:+00 +75:+00
Pi+0000 Oz+0089 Fo:10.0 MHZ CDU:UK TXT:  09-14-96 ver 1.9
XX
The first block is the output of the D*1 command.  Second block is D*2 command.  The Capital 'X's at the beginning and ends of the blocks are control characters.  Notice the ID00000.  That shows that the 'serial number' is 00000.  On my unit, you enter the serial number, but it's volatile.  Since it defaults to 00000, I just leave it there.

Then I went back to the comm link on the 5045A itself and eavesdropped on the conversation between the 5045A and the front panel.  4800, 7o2 with putty.  Here's the results at startup.  I've reformatted it, removed the control characters, and provided translation.

Code: [Select]

D*1 00030           // First main status data
W07 00030 400000000 // Set programmable output frequency to 10 MHz
T*2 00030           // Enable Remote Control (I think this means programming through this interface)
W01 00030           // Frequency Adjust ??           \ These should have numbers with them.
W02 00030           // C-field Adjust ??              |  Maybe no numbers = reset to zero
W10 00030           // Filter Order & Time Constant  /
W06 00030 000000000 // Zeeman Servo On
D*1 00030           // First main status data
D*2 00030           // Second main status data
D*1 and D*2 commands repeat forever
It's odd.  Why unit serial number 00030?  That's not the serial number of my 5045A.  But it works.

I then sent the 'D*1 00030' command from putty using the ALT key trick for the control characters and the 5045A gave the expected response.

So basically, it does work as documented.  Imagine that.

Ed

[hydrogen maser]

I got the wiring harnesses separated out and yes: the DB25 serial output from the 5045A is wired directly to the DB25 connector on the back and does not go into any of the 4040A electronics. There are only 8 wires total from the 4040 to the 5045A - 2 RF's and 6 other wires. Of the 6 other wires at least 2 of them have to be ground and power so unless there is some serial data going over the 4 remaining wires (perhaps major and minor alarm and initialization signals?) this thing is pretty simple in concept - just a power supply and RF distribution board combined with the 5045A in a box. Still mapping out what wires go where but it is a lot easier now that I have the 5045A out of the case.   

[hydrogen maser]

OK, now we are getting somewhere. The input voltage to to 5045A is 29V from the 4040 power supply. The high voltage power supply on the 5045A has two input terminal sets: 24V and 10V. The 24V input measures: 8.1V and the 10V input measures 3.5V. Yeah, that might be a small problem. Starting to look it is has come full circle - a power supply problem, but not in the 4040 in the 5045. Time to tear more things apart

[edpalmer42]

I don't know what you mean by 'the high voltage power supply on the 5045A'.  Do you mean the ion pump supply, the EM supply, or something else?

Notice that both power supplies are at 1/3 of their proper value.  I'm suspicious of coincidences like that.

I don't think you'll learn anything new, but there's a datasheet on the 5045A here:

http://www.gigatest.net/datum/5045txt2.pdf

Here's an interesting page that shows some data from a 5045A.

http://www.delphelectronics.co.uk/gps/datum.htm

Ed

[hydrogen maser]

I mean the ion pump and EM, and the below pic would explain why those voltages were so low.


 

[hydrogen maser]

If it is just the capacitors, then this will be an easy fix.

[Vgkid]

I see at least 6 bad caps. The one barely in frame is leaking from the bottom 
 If the yellow axials are not glued in ... then there will be some issues.

[hydrogen maser]

The yellow axials are glued in, and I don't think what looks like corrosion coming from that top cap is corrosion, I think it is glue because it is very hard and looks like glue. All the blue electrolytic caps have to go and I think they are glued on the base. Anybody have any tips for how to get glued caps out without damaging the board? Hot air?

[Vgkid]

Xacto knife after desoldering, wear safety glasses!
That is if the glue is still holding..

[edpalmer42]

The fact that it's still putting out voltage is a good sign that nothing else has fried.

The three yellow axial components that I can see in the picture are inductors.  I can see one is labelled 20uh.  Are there others I'm not seeing?

One minor nuisance in sourcing new capacitors is that with improvements in capacitor technology, you'll find that 220uf 50v capacitors today are smaller than the old ones and won't fit in the holes.  You might have to step up in voltage to get ones that fit.  Actually, that's not a bad thing.  Usually, the glue holding the capacitors isn't very good.  But in a piece of equipment at this quality level - who knows - epoxy?

I've never looked inside that power supply section.  Maybe I should! 

Ed

[Vgkid]

About those yellow axial caps 
Another option for those snap caps, would be switching to radial. With the appropriate lead spacing, useful for those snaps with multiple mounting leads. plus a lot more common.

[hydrogen maser]

The yellow axials (6 of them) are all 20uh inductors.  edpalmer42 - good tip on getting higher voltage caps to fix the size issue, I was wondering what I was going to do about that. It sure could not hurt to open up the power supply and take a peek, all you have to do is take out the screws on the top plate then about 6 screws in the board and tilt it up so the left side is down. There is a flex cable that ties that board to a lower board so just keep that in mind. Vgkid, you did not say the yellow ones were caps, you just said they should be glued down and they are Good tip on the radial, I can put anything in there as long as it is the same footprint or smaller, but I like edpalmer42's idea of going with a higher voltage rating, can't hurt.

[edpalmer42]

Look very carefully at those capacitors.  They might not be bad after all.  When I first saw the picture, I didn't think "leaking capacitors", I thought "water (or humidity) damage".  What do you see if you look at the input power lead on the ion pump supply with your scope?  How much ripple?  Maybe there is another fault in the power supply.

Ed

[hydrogen maser]

I am going to replace the caps before I do anything else. At least 6 of those caps have pretty serious corrosion going on - white powder on the top of them, discolored and lumpy, you can feel the bumpy surface on them. There may well be other problems with the power supply or other parts of the system but I am going to replace the caps first, they are not very expensive and then see what it looks like.   

[Vgkid]

I will usually overspec my caps when i replace them. Usually keeping the capacity the same, but sometimes 1.5-2X  larger. Mainly if there is alot of ripple still present.

[edpalmer42]

I took a look at my power supply board.  I remember now that I decided not to pull it because to do so, you have to remove the 5045A from the chassis to get at 4 screws on the side that attach the heatsinks to the chassis.  At that time, I had no reason to remove it.  Luckily, my board looks fine.  Date codes on the capacitors are 93 or 94.  One odd thing is that even though there is a bit of glue to supposedly hold down the capacitors, every one of them is spaced away from the board so they can wiggle and vibrate.  Of course, the glue is broken now.  Not impressed.

Ed

[hydrogen maser]

edpalmer42, your main board is different from mine. I see the STEL-1173 NCO on your board is in a socket. Did you install the socket or did it come that way?

[edpalmer42]

I was just going to post this message, but your question got in first.  I guess we're thinking in lock step. 

By the way, if you look in the background of the picture above, you can see half of an IC in a socket.  That's the STEL-1173 that typically fails with age.  I installed the socket so that if it fails again, replacement will be trivial.  If you look really carefully you can see a row of three surface-mount capacitors near the socket.  There's just room for a piece of paper between the closest capacitor and the socket!

Also, note the little 'mezzanine' board behind the socket.  HM, I didn't see this in your pictures.  It looks like they did a circuit mod and rather than hack and slash, they just abandoned the board and added a new one above where the old components were.  They used really stiff wires to connect up the new board to the main board and didn't need any more support.

Ed

[hydrogen maser]

The glue is really old and brittle on the caps, just wiggling them a little back and forth after desoldering breaks the glue bond and they are coming right out. Took a look at everything else and don't see any other obvious problems. bad power supply explains why basically nothing was working other than the oscillator, there must have been enough voltage and current for that to work. After I get new caps in it will be interesting to see what happens.

[hydrogen maser]

Yeah, I think these qualify as "bad caps". Some of them were so far gone that the pins just fell out of them during removal.

[edpalmer42]

What a mess.  I wonder why yours ended up in such bad shape compared to mine.  My caps are the same brand and series as yours, but they're about four years older.

Ed

[hydrogen maser]

Danno, perhaps it was in a harsh environment, high ambient temp, not enough circulation? I don't know the history of this device so who knows what has happened to it. Perhaps the PS went bad and then it was stored for years without any climate control? Not a single one of those caps is any good. Well, ONE of them looks ok, the one on the far left in the lower row but I'm not going to even bother testing it, no way I would trust it. Edit: OK so I did test it just to amuse myself - the one cap that looks ok reads just fine on the tester - capacity good, ESR less than 1/10 of an ohm, delta good. Sampled a few of the rest of them and they read what you would expect: little to no capacity and very high esr - hundreds of ohms and some in the kilo ohms. I wonder if that one little cap was doing all the work in the PS. The little cap that could. Shame it has to go to the graveyard with it's friends after putting up a valiant effort. Actually going to keep that little guy around and put him in a place of honor.

[Macbeth]

What a mess.  I wonder why yours ended up in such bad shape compared to mine.  My caps are the same brand and series as yours, but they're about four years older.

Ed

The date code of late '98 is awfully close to the cursed Capacitor plague that appeared in '99.

[hydrogen maser]

Hm, this doesn't seem right -  there is continuity across some of the capacitor holes on this board. I would not expect that to be the case. Unless some power supplies do that for some reason?

[Macbeth]

Hm, this doesn't seem right -  there is continuity across some of the capacitor holes on this board. I would not expect that to be the case. Unless some power supplies do that for some reason?

Continuity like very low ohms? Perhaps the rectifier diodes have shorted and you are measuring the transformer secondaries? Of course with no PSU circuit diagram to go on it's just a hunch. Easy enough to check.

[hydrogen maser]

Good call! D20 is shorted, pulling it out now.

[hydrogen maser]

diode is fine, something else in the circuit in parallel with the diode is shorted.

[Macbeth]

diode is fine, something else in the circuit in parallel with the diode is shorted.

...or in series, if D20 is actually a Zener

[hydrogen maser]

it is a multi layer board with the top and bottom layers being ground planes. Oh well, it was fun while it lasted.

[hydrogen maser]

This thing is weird. 4 caps shorted, but not all to each other. 2 caps (4 pads) have continuity between them as do another 2 sets of caps but there is no continuity between the two sets of shorted caps. I am tempted to just put new caps in there and if it blows up then it blows up. What do I have to lose at this point?

[Vgkid]

Could you try powering up the circuit externally?

[hydrogen maser]

It is all integrated together, there are basically 3 boards (not including stuff on the bottom). The mostly power board has a 20(ish) pin flex connector to a lower board (soldered on both ends) with a bunch of multipin connectors coming off that go everywhere else. There is even an RF connector on the "power" board. I guess I could disconnect everything from the bottom board and the RF from the "power" board, put new caps in it and let er rip. If it blows up then at least that top board was toast anyway and it won't hurt anything else other than itself and the lower board. That would spare the main board and all the other stuff from any harm. But if I do that and power it up and the magic smoke does not escape, that does not mean it will be ok to plug everything back in. Hm, what to do....

[Vgkid]

That doesn't make it easy. I was hoping that you could have been able to remove the power board, and power everything up from its connector.

[hydrogen maser]

Going to sleep on it and come up with a plan for how to proceed tomorrow. For all I know everything else works fine and I don't want to damage anything else. In the worst case scenario where I can't fix or determine why those caps are shorted I will proceed with replacing the caps in the "power" board, isolate the two small boards from everything else and power them from my lab power supply with current limiting and slowly turn up the current and see what happens. If they aren't fixable then I can wait for another broken 5045A to appear and hope I can scavenge parts and piece together something. From what I can tell the 4040A PS and electronics are ok (?). No need to rush this and break something beyond repair. I welcome any suggestions anyone has on how to proceed.

[edpalmer42]

I don't know if this will help, but I measured the voltage on both leads of the 15 capacitors.  There were a few odd values as you'll see.  I looked at each lead with the scope and there was no significant ripple or signal on any of them.  A few of the capacitors had component designations on the board, but most didn't so I added my own and included a picture with my labels.

                      C3           C4             C18        CA        C20         C19        CB        CC         CD          CE          CF           CG
Minus Lead    +77.5mv  +77.5mv   +17.60    0          0             0            0          0            -15.19   -15.22     0             +17.83
Plus Lead       +32.3      +32.3        +28.74   +5.22   +15.12    +25.80   +5.16  +25.76   0            0             +15.10    +18.72

                      CH         CI         CJ
Minus Lead    0            0          +17.63
Plus Lead       +4.96    +4.99   +18.76

All voltages were measured with respect to the chassis.  The minus leads of C3 and C4 are definitely not zero.  The others were within a few millivolts of zero so that's what I showed.  I double-checked the voltages on CG and CJ.  They're correct.  Very suspicious.

Based on what my unit reports for voltages, I'm making the following assumptions:

+ 5 volts:  CA, CB, CH, CI
+15 volts: C20, CF
-15 volts:  CD, CE
+24 volts:  C19, CC
System Voltage:  C3, C4

No clue what C18, CG and CJ are for.

Since mine is running right now (I'm doing a data run to compare the Cesium to my Rubidium house standard), I can't do resistance measurements to confirm that these capacitors are actually paralleled as I've shown.  I wouldn't be surprised to find multiple, independent outputs with the same voltage.  Check yours and correct as necessary.

Ed

[hydrogen maser]

The oddball ones on mine are:

CI - measures: 5.2 ohm across the terminals
CH - measures: 5.3 ohm across the terminals

CI + to CH + is 0 ohm
CI + to CH - is 5.5 ohm
CI - to CH + is 5.2 ohm
CI - to CH - is 0 ohm

It looks like CI and CH are in parallel

------

CG - measures: .2 ohm across the terminals
CJ - measures: .3 ohm across the terminals

CG + to CJ + is 0 ohm
CG + to CJ - is .2 ohm
CG - to CJ + is .3 ohm
CG - to CJ - is .1 ohm

It looks like CG and CJ are in parallel, but with so low resistance between all of those terminals, who knows

Scratching my head over this one.

[edpalmer42]

There aren't many things that get power from that board.  Have you unplugged whatever you can?  That would at least show you if the 'shorts' are within the power supply or in the rest of the 5045A.

I think I understand the low voltage across and high offset voltage for CG/CJ.  If you look here: http://www.ke5fx.com/cs.htm , John Miles says:

A 1-volt, 1-amp supply was applied to the hot-wire ionizer, elevated to 13.9V in accordance with the mass spectrometer specification marked on the tube.

He's working with a different brand of Cesium tube, but I bet the same applies to ours.  CG/CJ provides ~1V for the hot-wire ionizer.  My unit reports an ionizer voltage of 0V75.  It also reports a spectrometer voltage of 17V5.

Ed

[hydrogen maser]

I unplugged everything and the shorts went away. As I plugged each connector back in I watched the resistance on those 4 sets of pads and tracked it down to one of the large multipin connectors. If you are looking at the bottom of the unit with the HV power supplies on the left then there are three rows of sets of connectors to the right of the HV supplies. In the first row there are two connectors, the top connector is a 5 position connector with only the top 3 pins populated, and below it is a 15 pin connector with 14 pins populated. This 15 pin is the connector that causes the "shorts". The top wire is yellow and the next connector down is unpopulated. Wire numbers are counting from the yellow wire above the unpopulated position as being position 1. The tan wires 3 and 4 are spliced together in the wiring harness and the tan 10 and 11 are spliced together - these two tan conductors end up going into the cesium tube on the left side just below the HV supplies. There is almost a dead short on those tan wires of about .2 of an ohm. There is continuity from the negative side of CJ/CG to wires 3/4 and there is continuity from the positive side of CJ/CG to wires 10/11.

The two brown wires in positions 9 (ground) and 12 go into the right side port in the cesium tube, these have a resistance between them of about 5.5 ohms - these pins have continuity up to CH and CI 12 on the positive side of the caps and 9 (ground) on the negative side - that is where the low impedance "short" of a little over 5 ohms is coming from for those caps.

So I guess the question is, it is normal for it to be that way? I am not going to try to open up the cesium tube box and find out. Those are very low impedance paths that could draw quite a lot of current, is that normal?

[Vgkid]

.2 ohms is not much resistance, could be a shorted tantalum inside.

[hydrogen maser]

I am ordering the capacitors now. Of course I don't have exactly the capacitors I want to use for this and I don't want to cobble together something just because I am in a hurry and want to see what happens next. Get the right stuff. Trying not to get my hopes up too much on this one, I know the odds are stacked against me in a big way in making this thing work, but hey, this is all about fun and learning for me.

[edpalmer42]

Good news!

I measured across CG/CJ and got 0.2 to 0.3 ohms.  Across CH/CI measures 5.8 to 5.9 ohms.  Those values do not include any lead resistance.  So even though the readings are odd, it looks like they're good.

Ed

[hydrogen maser]

Thanks! Caps should be here Tuesday. I will put them in and report back. Thanks Ed!

[hydrogen maser]

IT IS ALIVE!

Kind of hard to see in the below pic, but the lock light is on




Thanks to everyone who has helped with this, but EXTRA SPECIAL BIG THANK YOU TO edpalmer42! Ed has put a large amount of time and effort into helping me and there is no way I could have gotten this far without his help. Thanks so much buddy! I know we don't even know if this thing really works yet or if it might have some unfixable fault or a bad tube but I consider this project to be a big success because I started out thinking that it was extremely unlikely that I was going to be able to get anywhere with this thing due to a lack of info about how it was built and how it works. I was just happy that it looked like the oscillator was working so it wasn't a complete waste of money. I learned a ton about how this thing works and I have confidence now that even if this one does not work correctly I can get more of these units until I get enough working parts to build one that does work. This thing is just way too interesting not to have one that works and I will get one that does work if this one does not, one way or another. Ed, what do you make of the output from the monitor program?   

[Vgkid]

Nice job. Fun following your progress.

[edpalmer42]

Sweet!  Congratulations HM!!  Why is there no emoticon for a happy dance? 

Looking at your numbers, I think everything looks good.  Probably the most important numbers would be:
- Power supply voltages (for obvious reasons)
- OCXO cmd - I think this is the EFC to the oscillator.  The range is +-4500 so yours is fine.
- Ramsey Level:  2500 +-500.  Maybe on the edge.  Watch this and see which way it goes.
- Zeeman level:  2000 +- 600.  No problem there.
- Pump current:  That's the ion pump.  Lower is better.  Yours will probably go to zero which is perfect.
- ShrtTerm StDv:  Range is up to 225 so 158 is fine.

The only thing I'm puzzled by is that the temperature is only 29.1.  On my unit, it's labelled as Cesium Module Temperature and tends to be about 20C above ambient.  Is your room really cold?

Now the big question is where do you go from here?  What was your reason for buying it?  Remember that whenever you're running this, you're using up the Cesium, so you don't want to let it run 24/7 without a good reason.  In particular, if your Ramsey Level stays low, it could mean that your tube is getting old so you want to be really careful with the runtime.  I'd suggest that you get either a Rubidium standard or a GPSDO and keep the 4040A on the shelf for occasional checks against the others.  A GPSDO would give you absolute confirmation that the 4040A is working properly, but I don't think it's really necessary.  A good Rubidium standard will probably give you better short-term performance than the 4040A or most GPSDOs.  A good OCXO will give you the best short-term performance of all of the above.

Congratulations again!  It's great to see a wonderful piece of equipment like that working properly and saved from the trash!

Ed

P.S.  If you'd like some more info on what all the parameters mean, check out this document:

http://www.ampere.com.mx/pdf/Manual_CsIII.pdf

It's the manual for a Cesium standard that's two or three generations newer than ours, but was made by the same people.  They used a lot of the same terminology as ours does.  It also talks about how their units work.  It's different than many other Cesium standards.

[hydrogen maser]

ShrtTerm StDv is up quite a bit now so perhaps there is more to repair? Ramsey level is going up after running for 4.5 hours and the ion pump is now at zero. That first pic was from when it had only been running for 24 minutes, the temperature has gone up now. Why did I buy it? Because it was relatively inexpensive and I like to repair broken equipment, I find it very satisfying. This thing looked really interesting and I could not really pass it up given the price. I knew it is was a very esoteric thing and I wanted to see how it worked. I figured that it would almost certainly not be fixable given the price but that it should have some interesting and unique parts in it and hey, who knows, maybe it would be fixable. Frankly I thought I would probably end up completely disassembling it and the oscillator would be useful at least if that part worked - I could use it to clock my frequency counters. This is the fourth piece of inexpensive non-working gear I have bought, the other three being my frequency counters and function generators. The function generator needed 8 new resistors at about 1 cent each, the frequency counters work perfectly, I did not have to fix them at all, I think the seller just did not know how they worked. The capacitors to fix the 5045A cost about $25, it could have been cheaper but I did not want to skimp on them on the off chance that it might actually work and fix this thing so I got really good capacitors. I have been really lucky in all my non-working for repair gear I have bought. There was one other reason I bought this thing, but that is for a different post I will make in the near future, I think it will be amusing to many.

[edpalmer42]

Yeah, that Shortterm StdDev isn't looking good.  Something's wobbling around more than it should.  Maybe it just needs to run a while to work the kinks out.  Now's the time you want to start logging some data.  For the time being, reset the alarms so that we can see if the unit thinks anything is really wrong and go into the 'graphics' mode so you can get a bit of logging.  Start by displaying the 4 power supply levels.  Make sure there's nothing intermittent with them.  For the other two items, look at the Shortterm StdDev and the Ramsey Level.

Ed

[hydrogen maser]

I cleared the alarm and have not seen an alarm since.



Ramsey level was very different this time, it started at 2800 and has been trending down, the opposite of what happened last time where it started at 2000 and went up. Shortterm StdDev looks better for now.

[edpalmer42]

Yes, that all looks fine again.  It's nice to see those stable voltages!  There's a bit of noise on the +5 line, but it looks okay.  Maybe it was just working out the kinks.  All you can do is watch it and see what happens. 

Maybe whip up a program that queries the unit and dumps the data to a log file so you can see if there are any glitches or trends.  Extra points if it parses the data and outputs it in some convenient format rather than just a raw data dump.

If you see the StdDev creeping (or jumping) up, look at the STEL-1173.  It puts out parallel data to the D/A converter beside it.  The failure mode is that the output drivers start to fail one by one.  If you grab the data sheets for both chips, you might be able to probe the connections with your scope and see if they're failing.  Yesterday, yours started to go strange after a few hours of operation.  If it starts to go again, maybe cooling the 1173 would bring it back.  I've noticed that it tends to run hot.  Maybe try a fan and/or a small heatsink, or as a last resort, gentle application of freeze spray.  Mine was totally dead when I got it so I wasn't able to see anything.  I guess that the best plan would be to check now, when everything's working, to see which outputs/inputs are active.  I don't think that all of them are used.

Ed

[hydrogen maser]

Yeah, that makes sense, measure what I can now while it is working. The serial port constantly spews data so no reason not to capture and save that data and to poke around in the 1173 and D/A and make some notes about what is what so that if/when I fails I will be able to tell if it is not working vs something else. Thanks so much again for all your help Ed, I could not have done it without you. 

[edpalmer42]

Glad I could help.  Have fun with your new toy!

Ed

[edpalmer42]

HM, now that you've got your 4040A working, maybe you can help me! 

While I was exploring and repairing my 4065A, I changed the value of a pot.  Now, I'd like to return the pot to it's original setting, but of course, I don't know what that was.   

If you look at the attached picture, you'll see a scope probe attached to an unlabelled test point near one of the corners of the main board.  This is the buffered signal that comes out of the Cesium tube.   The blue pot that's nearby (R49, I guess) is the one that controls the level. It's a complex signal that sits at one level and jumps up and down to other levels.  There's also a repetitive spike every 17 ms.  Could you look at yours and tell me the values of the various levels it jumps to - in particular, what is the base level that it's usually at?  They're in the 0 to -1 volt range.

Thanks,
Ed

[hydrogen maser]

Of course I will, leaving for work now - sometimes we call it early on Fridays, sometimes not, so I might be able to get to it this afternoon or I might not. If not today then tomorrow for sure. I assume you want measurements after it is locked? Assuming it will lock, I have not had any time to play with it since my last post and this will only be the third time it has been powered up post repair.

[edpalmer42]

Yes, I should have specified that it's after lock.  I have no idea what kind of mess you'd see before lock.     There's no rush.  I have family obligations for the long weekend so it'll be early next week before I can get back to it.

Ed

[hydrogen maser]

Totally forgot it was Easter, just drank coffee for a few hours and called it quits.

If I understand what you want to know, the top of that waveform usually sits right at zero volts. I used DC coupling and the little yellow "1" carrot next to tVmin on the left shows the zero volt mark. It is 20ms horizontal and 16mv vertical per division. The waveform is centered right at -80mv most of the time. When it jumps, it jumps by approximately 40mv positive or negative. I am having trouble triggering on the lower excursions because of the downward periodic spikes. That doesn't bother the trigger for the upper excursions but it is causing issues on the lower ones. I think there is a way to tell the trigger not just the level but the min width to trigger on, I will play with it and see. 

[hydrogen maser]

Better one that shows zero volts vs same relative position (approximately) for upper excursions.

[edpalmer42]

Thanks very much for that.  It'll be Monday or Tuesday before I can get back to mine.

Yours seems to be a lot noisier than mine.  I'll try and post a picture.  It'll be a bit of a challenge because I have an analog storage scope.  Actually, I have a USB scope that might do the job.  Got to think about that.  First challenge is 'where did I put it?'.   

Ed

[hydrogen maser]

Anything else you want me to look at while I have it running?

[hydrogen maser]

Looking pretty good on this run:

[hydrogen maser]

Ok, so the 4040A has at least one more problem or not? If you put it into storage mode and then later bring it out of storage mode you get a "Unit Restart Fault". It has always done this but I thought it was because the previous times I powered it down I removed the power cable to totally shut it down and it has complained about this before. In the manual it is Major Alarm 16 and it just says "Unit Restart" Perhaps this is not really an error and it is just letting you know that it was restarted? I assume these things are intended to be always running and never shut down? Just informational and not indicating that there was some problem?

[edpalmer42]

I can't think of anything else I'd like you to check, but thanks for asking.

As for the restart error, mine does that too.  Startup is always with a major alarm.  You reset it after lock.  I guess it's just to warn you that the power was off - otherwise you might not realize it.  That could cause major confusion in your analysis until you figured it out.  Right up there with having the power cord fall out.   

Ed

[uncle_bob]

Ok, so the 4040A has at least one more problem or not? If you put it into storage mode and then later bring it out of storage mode you get a "Unit Restart Fault". It has always done this but I thought it was because the previous times I powered it down I removed the power cable to totally shut it down and it has complained about this before. In the manual it is Major Alarm 16 and it just says "Unit Restart" Perhaps this is not really an error and it is just letting you know that it was restarted? I assume these things are intended to be always running and never shut down? Just informational and not indicating that there was some problem?

Hi

The HP5071A does the same thing. When it restarts it flags the fact to you can log the interruption. One assumption is that you ran out of battery power and may want to go buy another battery.

Bob

[hydrogen maser]

monitor3 software is interesting and useful (www.evoria.net/PRS45A/Monitor3.zip), it is windows based and runs just fine on Win7 pro 64bit. It will save all the data in a csv file and has better graphing. Some things don't work in this software: the alarm reset does not work and the download event log also does not work. I assume the event log download does not work because perhaps there is no event log for the model I have - there is no mention of an event log in the 4040 manual or the dos monitor software. It also misidentifies my model as being 4201A rather than the 4040A, I assume it is for later models and they did not even care about models from a different era, perhaps that is why the alarm reset does not work - it needs a slightly different command?.

[edpalmer42]

I forgot to mention Monitor3.  It doesn't work at all on my unit.  The doc file in the zip file confirms that it partially works on 5045A-based units.  I guess if I bypassed my user interface and connected directly to the 5045A that it would be usable on my 4065A, too.

Ed

[hydrogen maser]

Yeah, it says it does not work with the 4065, I also guess that is because the serial port on your 5045 is involved with the rest of your unit while it is not one mine. There are only 6 wires that go from the 4040 into the 5045 and initially I thought that perhaps it was really simple: one power, one ground, and the other 4 wires were just enough to carry out the 4 states that the 4040 displays: initialize, lock, major alarm, minor alarm through via simple open/closed or logic level states, but that appears not to be the case. 2 of the wires are ground, one power and I don't know what the other 3 wires do. I then thought those three wires might be serial data (still seems likely) but as soon as I touched the scope probe to one of the pins for those wires I heard a relay close in the 4040 and decided it was a little risky to be doing that so I left that alone.

[edpalmer42]

Here's my info on the signal level from the Cesium Tube test point.    My thought was that since yours was hopefully undisturbed, I could adjust my level to equal yours. Since I now have your info, I decided to play with mine. 

If I'm reading yours correctly, your baseline is -100 mv, your jumps are plus and minus 50 mv from the baseline, the spikes peak at -250 mv, and the noise level is 200 mv p-p.

First, the sense of the pot is backwards.  Clockwise decreases the level, CCW increases the level.  If I adjust mine for a 100 mv baseline, my jumps are -75 mv, +25, +50, and +75 mv. (!), the spikes peak at -175 mv, and the noise level is only 50 mv p-p.  If I use the 20 MHz bandwidth limit, the noise level drops to 30 mv p-p.  Nothing else changes.  I often have to use the BW Limit because there's a local FM station that regularly shows up on my scope.   

Adjusting the baseline more negative than ~-200 mv causes errors 02, 07, and loss of lock.  Adjusting the level at all changes the Ramsey level which changes everything else.  There's a slow servo (many minutes) that tries to return the Ramsey Level to 2500. 

I had to go old school to get these pictures.  The vertical scale is 50 mv / Div.  Horizontal is 10 ms / Div.  The 20 MHz bandwidth limit is engaged.  The baseline is -100 mv.  One of these days I've got to get me one of them new-fangled digital oscilloscopes.  The problem is that this ornery old HP 1744A analog storage scope just won't die and give me an excuse!  It's over 30 years old for crap sake!  What do I have to do, drive a stake through its heart? 


I'm not sure what this tells us, if anything.  Is your tube on its last legs?  Is there a subtle fault in your unit causing higher noise levels?  Yours is serial #02350, mine is #01067.  Mine has that mezzanine board, but yours likely has those circuit changes already rolled into the main board.  Even though yours has more noise, you're getting better StdDev values than I am.  Do I have a noisy circuit in my unit?  You're seeing numbers in the 130 - 140 range while I'm getting 170 - 180 although it seems like that number changes everytime I run the unit.  Now that I've got the level set I'll have to see if it stabilizes.  Maybe there's a sweet spot for that level adjustment.


Ed

[hydrogen maser]

Hm, your traces look quite different from mine, perhaps some of it is due to the "nosier" nature (appearance anyway) of digital scopes or perhaps it is something different in my unit as we do not have identical main boards.

[edpalmer42]

Does your Rigol have a 20 MHz Bandwidth Limit?  If so, what does your signal look like with it engaged?  I have no idea what bandwidth the buffer uses.  I can't find any data on the buffer chip which, I think, is U27 - a Burr-Brown 49522 in my unit.  Since the important features seem to be the DC levels rather than the slopes, I don't think it's a high bandwidth circuit.  The slew rate on the spikes is only about 0V050 per ms, i.e. 50 volts per second.

Ed

[hydrogen maser]

I will take a look at it with bandwidth limiting after I look into something here. Remember those 4 caps that I was (as it turned  out unnecessarily) worried about because of the low impedance on them? Looks like one of them might not be working. Because the noise on the 5v rail was higher than all the other rails I thought it was worth looking into that. I went back to check the voltages on all my caps vs what your unit shows and am seeing some strange results. It might be that it is just because it has not locked yet, I will take a look at it after it locks. 

[hydrogen maser]

Well this looks very wrong. Cap CI reads -1.28v on the POS lead and zero on the neg referenced to ground or just itself floating. CI is in parallel with CH - CH reads +4.89 on the POS lead and zero on the neg. What the heck is going on? And no, I did not put CI in backwards, unless the silkscreen is reversed from what it should be on both sides of the board. I had trouble with the positive pads on both sides of the board for CI, they lifted off because there are not any top or bottom traces for it, just on the internal layers and some of those old caps were a little stubborn about coming out.

[edpalmer42]

Looks like the plus lead on CI isn't connected.  Did you check for continuity?

Remember that your values won't be quite the same as mine.  I'm going to modify my guesses on what the voltages are for:

+ 5 volts:  CA/CB, CH, CI
+15 volts: C20/CF
-15 volts:  CD/CE
+24 volts:  C19/CC
System Voltage:  C3/C4
Cs Oven:  CH/CI
CG/CJ minus lead to gnd:  Mass Spec voltage
CG/CJ :  Ionizer voltage
C18: Unknown

For the Mass Spec and Ionizer voltages, the D*1 command reports the readings, the D*2 command reports what they should be.

Ed

[hydrogen maser]

The problem with electronics repair is that humans are not well equipped for it because you often need three hands. Think I see what might be the issue.

[hydrogen maser]

Yep, my lifted pad via repair skills suck. I was in hurry because I got excited, it was looking like this thing might be fixable and I did it the very easy way and just stuffed as many lead wires as would fit in the via - test for continuity and shorts - good - soldered it - test for continuity and shorts - good. But it did not take because I think I did not flow enough solder into the joint and it just had a mechanical connection. Put more flux and more solder on the joint and it tests good now, but given that it looks like this device works I think it is time to step back - remove that cap - and do a proper via repair (a new skill to learn ). Alternatively I could just remove the cap. The old cap was a 220uf in parallel with another 220 and all the 220's got replaced with 470uf so a single cap should work fine in this case as long as the multiple internal traces (it looks like there are two) that go to the positive side of that cap don't mind being disconnected from each other (if they are) and the 5v rail at that point.   

[edpalmer42]

It's just a power supply capacitor.  If you'd used 220uf capacitors, I'd suggest adding a jumper wire between CH and CI.  Since you doubled the size from 220 to 470 I'd just leave it alone since it *is* working.  The more soldering you do on an old board, the more traces and pads will suffer and the more likely that something will go horribly wrong!

Ed

[hydrogen maser]

I put it all back together and that cap measures OK now - same as its twin. Everything looks good since it has locked. No significant differences in this run since the last one. Ed: I looked at that waveform with 20mhz bandwidth limiting and it does not look that much different than it did before on my scope, it certainly does not look like the waveform images you posted. Don't know what to make of that.   

[edpalmer42]

I wouldn't worry about it.  It's locking and you're getting good StdDev readings so, for now, I think you're good to go.  Keep some notes and logs showing the current status and watch for variations and trends.  Power it up for an hour or two every six months to let the ion pump keep the tube healthy and hopefully, it will provide good service for many years.

As Dave would say, "Winner, winner, chicken dinner!"

Ed

[hydrogen maser]

All the voltage rails look better now, yet to be seen what happens with deviation. 

[edpalmer42]

Hi HM,

I just stumbled across a piece of information on your Cs tube that I thought you'd like to have, if you haven't found it already.  I got it from the Wayback Machine searching for www.ftsdatum.com .  The rows of periods are part of the quote.  I didn't cut anything out.

Model FTS 7100 Series . . .

. . .provides standard cesium performance with an expected life of between eight to eleven years. Used in our own instruments, these tubes also fit Hewlett Packard HP5061A or B Cesium Instruments and FEI Cesium Instruments. In either case, the tube is a drop in replacement. Contact your local representative or FTS directly for more details or a quotation.

Model FTS 7500 Series. . .

. . . provides standard cesium performance with an expected life of between ten to thirteen years. Used in our own instruments, these tubes also fit Hewlett Packard HP5061A or B Cesium Instruments and FEI Cesium Instruments. In either case, the tube is a drop in replacement. Contact your local representative or FTS directly for more details or a quotation.

Model FTS 7600 Series. . .

. . . . . .available in two basic configuration. The first configuration is a high performance cesium tube with an expected life of between four to five years, and the second is an extended life tube providing standard performance with a life expectancy of fifteen to twenty-two years. Used in our own instruments, these tubes also fit Hewlett Packard HP5061A or B Cesium Instruments and FEI Cesium Instruments. In either case, the tube is a drop in replacement. Contact your local representative or FTS directly for more details or a quotation.

My tube is model #7504A.  Yours is #7614-1 ( -10?  Not sure.).  So now, is that the high performance / short life version or the standard performance / long life version??    Not sure, but the fact that your unit doesn't say anything about having the high performance option is promising.

I tried Monitor3 and it works on mine when I connect directly to the 5045A module.  I'm going to see if I can hack the program to run when hooked to the rear connector, i.e. to the 4065A port rather than the 5045A port.  Here's a screen with a few of the more interesting parameters.  I have no idea what caused the spike in the Clock & Zeeman signals.  But it had almost no effect on the variance or the output.

Ed

[hydrogen maser]

Perhaps a rs-232 splitter? My tube is the FTS-7614-12, can't find anything on any of the other part numbers yet, still looking. I'm hoping mine is the long life one, seeing as how mine is one of the simplest 4000 series and has no options installed in it, it does not look like anything special, but who knows. Found some interesting docs in the wayback on the 5045A - the pdfs are still there and accessible.

https://web.archive.org/web/19990221231232/http://www.datum.com/res_technical.html

Right now I am mapping out all the wiring that comes out of the 5045A because I think the 4040A chassis is really unnecessary and I want to see if the 5045A will run without it and just a lab power supply but I need to figure out how the run/storage signals are being sent into it, or I guess I could just take the 5045A out, power it up and see what happens on the serial port. Would not surprise me if it was happy with that and went right into initialize and run. Taking a while because I have not had a lot of time to play with it.   

   

[edpalmer42]

An rs-232 splitter might work, but I'd rather just connect to the existing port on the back.  I want to compare the query/response chatter between the 5045A and the computer vs. the 4065A and the computer.  I also have to check that I'm not having yet more rs-232 connection problems.  It also looks like Monitor3 will accept COM ports higher than 9, it just won't work with them! 

According to the data sheet for the 5045A, all it needs is 18 - 64 volts at 30/55 watts (operating/warmup).  But I don't have any detailed info on the connections.  To check the storage mode, look for leads into the 5045A that change state when you plug in the AC cord while switched to storage mode.  Power for the ion pump has to get in there somehow.

Ed

[hydrogen maser]

Figured out how the run/store works. The DB15 that goes into the power supply section of the 5045A on my unit is wired as such: Only 4 pins populated in the wiring connector - Pins 1 and 5 are ground, pin 8 has 29V applied when in run mode and zero volts in storage, pin 10 has zero volts in run mode and 29v in storage. Pretty simple and it makes sense that there are only power and ground wires going into the power supply board for 5045A. There are only two other wires connected from the 5045A to the 4040 chassis. The other DB15 that comes off the main board on the 5045A has only two pins populated in the connector attached to it, pins 14 and 15. These almost have to be serial data and it would make sense that serial data would come from the main board. Spent a good amount of time untangling all the 4040 wiring and getting it separated into different bundles grouped by purpose. It was worth doing because there are not that many different wire colors and it was really confusing about what went where. Making progress.

[edpalmer42]

On my unit, the 5045A has a DB-25 connector with 3 wires for the serial data (xmit,rcv,gnd), then a DB-15 with 2 wires for something, then a DB-15 with 4 wires to the power supply.

It doesn't look like I'll be able to hack Monitor3 to work with my unit.  I hoped it was something like a signature that was different between the 5045A and the 4065A, but it turns out that the 4065A puts out more data so a simple hack isn't possible.  Wiring out the 5045A isn't an option because if I do that, I'll lose the front panel display.  I think I'll throw together a program that polls the unit through the rear panel, parses the data, and puts out a file in the same format as Monitor3.  That will allow me to use Monitor3 or any other plot program to display the data.

Ed

[hydrogen maser]

Ed, you were saying:  "The ion pump won't run in storage mode." in an earlier post. You might check that you have voltage/no-voltage swapped between pins 8 and 10 of the 5045A PS DB15 when in storage mode vs run mode. If there is no voltage (or not enough voltage+current) on pin 10 when in storage mode that might explain why the ion pump was not running in storage mode.

[hydrogen maser]

My long term plan for this device is that I would like to have a display on the front with the time (7 segment LED's?) + a touchscreen display running monitor3 and/or whatever software on windows 7). Should be able to get thin versions of both of those things and bolt on the front, serial to the touchpad, perhaps arduino or raspberry to hook into the main serial or this other mystery two wire for 7 segment or other stuff. Not going to be a quick project, but I don't see why it is not doable. Can also use NTP on the touchpad via wifi to get approximate current time for sync, not entirely all thought out yet. Should be fun.

[edpalmer42]

My long term plan for this device is that I would like to have a display on the front with the time (7 segment LED's?) + a touchscreen display running monitor3 and/or whatever software on windows 7). Should be able to get thin versions of both of those things and bolt on the front, serial to the touchpad, perhaps arduino or raspberry to hook into the main serial or this other mystery two wire for 7 segment or other stuff. Not going to be a quick project, but I don't see why it is not doable. Can also use NTP on the touchpad via wifi to get approximate current time for sync, not entirely all thought out yet. Should be fun.

Sounds like some interesting upgrades, but I wouldn't do that much work for a Cesium.  I use an Efratom FRT Rb standard as my house frequency standard.  It runs 24/7 and I distribute the signal to all of my test equipment that can accept a 10 MHz input as well as using it for a precision 10 MHz source.  I suggest that a unit like that would be a better candidate for the kind of upgrades you're considering rather than a Cesium that will only occasionally be turned on.

I think some models of Cs standard have an 'OCXO mode' where the Cesium tube is powered down, but the OCXO is hot and online.  If you hacked the 5045A so that was possible, then your upgrades would provide more value.

Ed

P.S.  I see that this message thread has over 4600 views.  I'm assuming that at least some of you lurkers have a 5045A-based Cesium unit.  This isn't a private conversation, you know.  If you have any questions or info to add to the conversation, please contribute!

[hydrogen maser]

Ha Ha, I know. This is more like eavesdropping on two hackers discussing the minutia of their technical conversation. I think it is valuable that this be public. I can't find almost any technical documentation on the 5045A or the 4040A/RS and little things like the pinouts of the various connectors could be very helpful to someone in the future and save them a lot of time in troubleshooting these devices.

[Vgkid]

It would definetly be more beneficial to keep the ocxo powered on continuously, instead of the cs tube.

[hydrogen maser]

Surely (and don't call me Shirley ) that could be done, saw it happen when the 5045A PS was bad, a little hacking called for Vgkid, added to the list

[edpalmer42]

Hi Shirley 

(I think we're showing our age as well as our weird sense of humor!) 

The trick would be to deal with the EFC.  It's controlled by the processor.  Do you power down the processor?  If you do, you lose voltage to the EFC which will cause the oscillator to be off frequency.  Do you keep the processor active?  It's going to change the OCXO frequency to try and find the Cesium signal.  In a perfect world, the processor would learn the OCXO's aging and compensate for it during OCXO-only operation.  Some GPSDOs do that during holdover.  But that would require reverse-engineering the code and adding to it.  You'd have to reverse-engineer the code just to build in a minimal OCXO-only mode where the EFC voltage was frozen.  That almost sounds like work.  Ugh! 

Other than having the signal available at all times, it isn't clear to me whether having the OCXO running continuously would have any effect on the performance.  Normally, you should run an OCXO continuously because aging will drop down to a very low level.  Top grade OCXOs can have aging rates in the e-12 per day range after long periods of continuous operation.  I've never seen any info on whether AlDev or Phase Noise improves with continuous operation.  In a Cs standard, aging is irrelevant.  AlDev or Phase Noise improvements may or may not be relevant depending on how the servo loop affects the OCXO's frequency.

Ed

[hydrogen maser]

I have a simple plan - power down everything else and control the OCXO via an external EFC. Where would I get the EFC signal characteristics from? From a hybrid rubidium/GPS/OCXO or some such. It does not need to make any sense from a cost/production standpoint it just has to be interesting and fun. So now two touchscreens - one for the GPS/rubidium/ocxo to see what it is doing and another for the for the cesium and well, there is not enough space so some external output to see how they correlate. Just thoughts. Still going step by step but learning how the 5045A behaves and how to integrate it into other systems. This would be lots easier if there was a service manual for the 5045A (obvious now that the 4040A chassis is not needed) but what fun is that? So, perhaps a system bus based system with the 5045A in a slot, an OCXO, a rubidium, a GPS, hmmm, what else? They can all live in harmony on the bus. Yeah, that sounds like an interesting project, go big or go home as we like to say here in America. Why not? Bus timing, contention, etc would seem to be the biggest issue but I am sure that has been solved somewhere. Yes, I like that idea, ditch the 4040, put a bunch of different timebases on some sort of bus and then, well who knows what havoc would ensue, sounds like fun to me.

[TheSteve]

There are lots of views because many of us would love to have a cesium frequency standard and we probably all dream of finding one cheap. Assuming we do see a deal on one at least there is now some useful info documented. I have multiple GPSDO's and rubidium standards but cesium would be more fun.

[dakiller]

I got a HP5061A sitting collecting dust. Picked it up for ~$200 not working years ago. It probably just 'ran out' and was decommissioned, so it hasn't been 'played with'

I don't know if one day I might want to get it working again.

[edpalmer42]

I got a HP5061A sitting collecting dust. Picked it up for ~$200 not working years ago. It probably just 'ran out' and was decommissioned, so it hasn't been 'played with'

I don't know if one day I might want to get it working again.

A Cesium tube will die if you just leave it in a corner.  Pull it out NOW and get the ion pump running.  The 5061A manual gives you the details.

Ed

[edpalmer42]

I have a simple plan - power down everything else and control the OCXO via an external EFC. Where would I get the EFC signal characteristics from? From a hybrid rubidium/GPS/OCXO or some such. It does not need to make any sense from a cost/production standpoint it just has to be interesting and fun. So now two touchscreens - one for the GPS/rubidium/ocxo to see what it is doing and another for the for the cesium and well, there is not enough space so some external output to see how they correlate. Just thoughts. Still going step by step but learning how the 5045A behaves and how to integrate it into other systems. This would be lots easier if there was a service manual for the 5045A (obvious now that the 4040A chassis is not needed) but what fun is that? So, perhaps a system bus based system with the 5045A in a slot, an OCXO, a rubidium, a GPS, hmmm, what else? They can all live in harmony on the bus. Yeah, that sounds like an interesting project, go big or go home as we like to say here in America. Why not? Bus timing, contention, etc would seem to be the biggest issue but I am sure that has been solved somewhere. Yes, I like that idea, ditch the 4040, put a bunch of different timebases on some sort of bus and then, well who knows what havoc would ensue, sounds like fun to me.

In a way, you've already got the bus.  Take a look at the manual for the 4065C Cs Standard here:

http://www.ko4bb.com/getsimple/index.php?id=download&file=02_GPS_Timing/FTS_4065C_Caesium_clock_Operator_Manual.pdf

On the 97th page of the pdf there's a drawing showing you how to daisychain multiple Cs standards onto a single RS-232 link.  That's why our units have ID numbers - so you can query them seperately on the same bus.

So make the serial bus your system bus with one address for the 5045A, another for the GPS, etc.  You might want to keep the 4040A as a chassis to keep everything together.

Ed

[edpalmer42]

There are lots of views because many of us would love to have a cesium frequency standard and we probably all dream of finding one cheap. Assuming we do see a deal on one at least there is now some useful info documented. I have multiple GPSDO's and rubidium standards but cesium would be more fun.

HM and I both seem to have won the lottery.  As I said earlier in the thread, used Cs standards are usually dead because the Cesium supply has been exhausted.  Maybe these 5045A-based units are the exception.  Mine had a fairly typical fault for the breed.  HM's bad power supplies are just too weird.  I can't imagine what kind of life his led to have capacitors cooked that badly.

Ed

[dakiller]

I got a HP5061A sitting collecting dust. Picked it up for ~$200 not working years ago. It probably just 'ran out' and was decommissioned, so it hasn't been 'played with'

I don't know if one day I might want to get it working again.

A Cesium tube will die if you just leave it in a corner.  Pull it out NOW and get the ion pump running.  The 5061A manual gives you the details.

Ed

Even if it has been off for probably a decade?

[edpalmer42]

I got a HP5061A sitting collecting dust. Picked it up for ~$200 not working years ago. It probably just 'ran out' and was decommissioned, so it hasn't been 'played with'

I don't know if one day I might want to get it working again.

A Cesium tube will die if you just leave it in a corner.  Pull it out NOW and get the ion pump running.  The 5061A manual gives you the details.

Ed

Even if it has been off for probably a decade?

Probably too late, but if you don't try, you won't know.  Actually, it would be a very interesting and useful test.  How long can you leave an HP Cesium tube and still recover it?

Ed

[hydrogen maser]

Confirmed: if you have a working 5045A all you need is a power source for it. It does not rely on any external circuitry or commands. Just apply power to pin 8 and ground to pins 1 and 5 of the db15 of the PS input and it will go right into initialize and run. Apply power to pin 10 for storage mode to run the ion pump (mutually exclusive - apply power to only one of these two pins at any particular time).

The two mystery wires coming off the DB15 on the main board are still mostly a mystery. Pins 14 and 15. Pin15 always has 3.5v dc on it with a small ac (60ish mv) signal on it. Pin14 is low during initialize and goes to 3.5vdc with the same 60 mv ac component (just noise?) after it locks. They are NOT rs232 or any serial data that I could figure out. My guess (just guesses) are this: on my unit the major alarm and initialize lights always both come on during initialization. Perhaps they are tied together and both light when pin 14 is low? Initialize would seem to be a "major alarm" in that your unit is not working right now and it is something you would want to know via the alarm relay contacts and led, so it makes sense that it would do that. After it locks the major alarm light goes out, but should it? Because there is always a major alarm 16 unit restart that needs to be cleared in the rs-232 interface. Again, perhaps it is the difference in philosophy between a software major alarm and a hardware one. The hardware is working after init so no need to signal a major alarm via the led or relay contacts? Perhaps pin 15 that is always at 3.5V is the minor alarm signal, I have never seen a minor alarm and that would match Pin 15 always high. However this line of thinking leaves out one possibility: how is a major alarm signaled (outside of initialization?)

We have 4 possible states of voltages on these two pins and that is enough (2 bits) for four possible states:

Confirmed states:
both low (disconnected or in storage mode or no AC or DC power) = no leds lit
both high = only lock led lit
pin 14 low and pin 15 high: initialize and major alarm lit

Unknown:
pin 14 high and pin 15 low: ? major alarm or minor alarm?

It still does not quite add up. There is one other possibility I can think of, another state where both pins are low but not disconnected - that is a possible different state. Or perhaps major alarm is a different voltage level? it could be more complicated than it appears because I have not seen all the different states possible.

[hydrogen maser]

I don't see any way that I can force a minor or major alarm without serious meddling in the hardware so I am just not going to worry about it. Pins 14 and 15 off the db15 on the main board can be disconnected without any problems and I can get all the data I need from the serial port so why worry? I am kind of in this reverse-engineering documenting mode at this point and a little one minded about that but it is not important to me to know about this aspect of how it works. I know now how to power and control the 5045A even if the 4040 has problems or dies so it is all good, so now, on to the fun part: what to do now? Hmmm.....

[KE5FX]

I got a HP5061A sitting collecting dust. Picked it up for ~$200 not working years ago. It probably just 'ran out' and was decommissioned, so it hasn't been 'played with'

I don't know if one day I might want to get it working again.

A Cesium tube will die if you just leave it in a corner.  Pull it out NOW and get the ion pump running.  The 5061A manual gives you the details.

Ed

Even if it has been off for probably a decade?

Probably too late, but if you don't try, you won't know.  Actually, it would be a very interesting and useful test.  How long can you leave an HP Cesium tube and still recover it?

Ed

The longer you wait, the more extreme measures are necessary.  It's important not to give up too quickly.  I wrote about one case here.  Unfortunately that tube died with an open filament shortly after I installed it in the 5062C, but a couple of other Cs tubes that needed even more "rejuvenation" cycles proved to be reliable.

In my limited experience, about 50% of the tubes that can't be restored with the Cs standard's built-in power supply can still be brought back to life with a more powerful external  HV supply.  The others can't be pumped down no matter how long you try.

[edpalmer42]

The longer you wait, the more extreme measures are necessary.  It's important not to give up too quickly.  I wrote about one case here.  Unfortunately that tube died with an open filament shortly after I installed it in the 5062C, but a couple of other Cs tubes that needed even more "rejuvenation" cycles proved to be reliable.

In my limited experience, about 50% of the tubes that can't be restored with the Cs standard's built-in power supply can still be brought back to life with a more powerful external  HV supply.  The others can't be pumped down no matter how long you try.

I've also heard people say that even though the tubes are so exhausted that you can't read the beam current on the meter, the thing still locks.  So even a 'dead' tube might be usable, although maybe with a less-than-stellar noise level.

I think the differences between the HP tubes and the Datum/FTS tubes are quite intriguing.

HP:        relatively leaky, 40 ua ion pump
Datum:  relatively tight , 240 ua ion pump

I think at one point I said that Datum used a 300 ua. ion pump.  I don't know where I got that number.  A current reading of >240ua is a major fault that will shut the system down.

Maybe the Datum tubes aren't really that tight.  They just put in a beefier ion pump so that they can pump the tube down quicker.  I've seen a peak current of ~140 ua. after being off power for months.  Actual value might be higher.  My measurement technique is still evolving as I learn more about how the thing behaves.

I wondered if there was anything interesting to see inside the ion pump power supply so I popped the cover to take a look.  The whole thing is filled with white rubbery potting compound.  Well, at least I "took it apart".   

Ed

[Macbeth]

I got a HP5061A sitting collecting dust. Picked it up for ~$200 not working years ago. It probably just 'ran out' and was decommissioned, so it hasn't been 'played with'

I don't know if one day I might want to get it working again.

Yeah, that's a pretty shitty standard as these things go. I mean it only has a 5MHz output. My old FM radio has a 10.7MHz IF oscillator, yo!

Also that old analogue clock face. I mean come on? Not even Nixies? Maybe you could put some blue leds behind the clock to jazz it up a bit?

I think some dudes used some of those HP5061As to give Einstein a run for his money 

[hydrogen maser]

Maybe the Datum tubes aren't really that tight.  They just put in a beefier ion pump so that they can pump the tube down quicker.  I've seen a peak current of ~140 ua. after being off power for months.  Actual value might be higher.  My measurement technique is still evolving as I learn more about how the thing behaves.

I was surprised that the ion pump current on my unit was so low the first time I powered it up after repair  given the universal advice to pump down the tube after long term storage. It was 1ua on my unit on the first run and the next run it went to zero and has been ever since. On first start I thought this was a sign that something was very wrong because I assumed that my unit had not been powered up for quite a long time given the state of the PS and I thought that the ion pump or something else was not working. Perhaps I have the long life tube or the FTS tubes are just generally good in that regard. Don't know enough about it to have an opinion but it is an interesting little anecdotal point.

[edpalmer42]

I got a HP5061A sitting collecting dust. Picked it up for ~$200 not working years ago. It probably just 'ran out' and was decommissioned, so it hasn't been 'played with'

I don't know if one day I might want to get it working again.

Yeah, that's a pretty shitty standard as these things go. I mean it only has a 5MHz output. My old FM radio has a 10.7MHz IF oscillator, yo!

Also that old analogue clock face. I mean come on? Not even Nixies? Maybe you could put some blue leds behind the clock to jazz it up a bit?

I think some dudes used some of those HP5061As to give Einstein a run for his money 

Macbeth, you're only allowed to dis somebody's Cs if you've got a better one.  Well?  We're waiting.        

And that analogue clock?  It's actually made by PATEK PHILIPPE.  Search for that name on ebay.  Hold on to your shorts!  I think that because this one is an unusual product from the company, it's interesting to people who collect that brand.  "And here's my latest acquisition.  An exquisite Patek Philippe clock installed in some weird piece of junk." 

Ed

[edpalmer42]

Maybe the Datum tubes aren't really that tight.  They just put in a beefier ion pump so that they can pump the tube down quicker.  I've seen a peak current of ~140 ua. after being off power for months.  Actual value might be higher.  My measurement technique is still evolving as I learn more about how the thing behaves.

I was surprised that the ion pump current on my unit was so low the first time I powered it up after repair  given the universal advice to pump down the tube after long term storage. It was 1ua on my unit on the first run and the next run it went to zero and has been ever since. On first start I thought this was a sign that something was very wrong because I assumed that my unit had not been powered up for quite a long time given the state of the PS and I thought that the ion pump or something else was not working. Perhaps I have the long life tube or the FTS tubes are just generally good in that regard. Don't know enough about it to have an opinion but it is an interesting little anecdotal point.

I don't think the long life tube is any tighter.  AFAIK, the only thing that makes a tube 'long life' is having more Cs in the oven.

I don't think you mentioned where you got your unit from.  If the previous owner knew a bit about Cs standards, they may have left it plugged in on standby to try and fix it.  When that didn't work, they sold it.    It'll be interesting to see what happens if you leave it unplugged for a few months.

Ed

[Macbeth]

And that analogue clock?  It's actually made by PATEK PHILIPPE.  Search for that name on ebay.

Blimey! I don't need to, I mean I love my Russian clone of a Swiss "31 jewel" watch. 2416B "Vostok Amphibian" for the win!

But the Cs sitting on a shelf. That alone would have horologists up in arms knowing a cesium standard is left gathering dust! 

Of course when I need accurate time then a Casio watch and my Symmetricom GPSDO are more than good enough 

[hydrogen maser]

I don't think you mentioned where you got your unit from.  If the previous owner knew a bit about Cs standards, they may have left it plugged in on standby to try and fix it.  When that didn't work, they sold it.    It'll be interesting to see what happens if you leave it unplugged for a few months.

Ed

I got it from BMI surplus, I had been watching it for a while but they wanted $3300 for it and I was not going to pay that amount for it. They have a feature where you can make them an offer if you don't like the price they have posted for something, so on a whim I made a very low-ball offer mostly just to see how they would respond. Would they tell me to get lost or be nice about it, etc. Very much to my surprise they said, ok - we are changing the price, you can order it if you want, so I did. I doubt they knew anything about it and that it should have been run in storage mode and even if they did, the PS was not working and I doubt the ion pump worked.
 

[hydrogen maser]

Been thinking about what to do with the 4040 and I think I have decided not to modify it at this point. I think the best "upgrade" to do to it is to get a 4065C with a dead 5045A in it and swap my good unit in. Should be a piece of cake if the 4065C chassis is working. I don't see any 4065C's for sale out there so if someone knows where I could get one or sees one in the future, please PM me.

[edpalmer42]

Been thinking about what to do with the 4040 and I think I have decided not to modify it at this point. I think the best "upgrade" to do to it is to get a 4065C with a dead 5045A in it and swap my good unit in. Should be a piece of cake if the 4065C chassis is working. I don't see any 4065C's for sale out there so if someone knows where I could get one or sees one in the future, please PM me.

Are you looking for a 4065(A, B, or C) for the user interface?  If so, yes, it looks nice, but I'll be setting up a program to log the data off the RS-232 port.  I think that's much more valuable than a pretty face.  I'll probably add some checking for alarms and things drifting out of limits.  Basically, I'll be replacing the internal user interface with an external one that has the features I want.  That's exactly what you were planning.  That big blank spot on the front panel of the 4040A is just screaming for an LCD display.  Wouldn't something like this look great there? 



Ed

[hydrogen maser]

Hm, maybe you are right, it won't be easy to find a 4065 for a good price or at any price given how rare they are to come onto the surplus market. A DIY display is doable and would be more useful than the 4065 interface. There is plenty of unused space on the front of the 4040. I will look into it.

[edpalmer42]

It does seem like Datum units aren't common.  I'm surprised and a little disappointed that we haven't heard from anyone else who has one.

The bezel in the picture is for a 3.2" LCD, but I'm wondering if a better way to go is with a 7" or 8" Windows tablet.  A few things to think about are:

- Cost can be < $100 (ebay).
- Use USB/serial adapter to connect to the 4040A's serial port.
- Drill one or two small holes in the front panel of the 4040A for USB and power cables.
     -Right angle cables would be sweet if you can find them!
- Use velcro or magnetic sheet to hold the tablet to the front panel.
- Can run Monitor3.
- Touchscreen means you could create your own program with whatever buttons you need.
- Forget about GPS to get the time.  Windows/Wifi can use NTP.
- Log data to internal flash.

A few issues/concerns

- Battery will die while the unit is powered down (assumes a day or two of operation every few months).
     - Cllock will be wrong since tablets usually don't have a CMOS battery - Windows doesn't like that.
     - Could keep it plugged in (storage mode).
- Monitor3 won't be very easy to read on a small screen.  A custom app tailored to the screen size would be better.
     - Could use VNC or remote desktop to view the screen from a different computer with a larger monitor.
         - You could even use a tablet with a broken screen!

Ed

[hydrogen maser]

Yes, I am surprised also that you and I are the only FTS/Datum owners here that want to discuss these units. I know how rare it is for a hobbyist to own a working Cesium standard so perhaps it is not that surprising after all. I get the impression that the 5045A is a pretty robust piece of hardware in general (other than the 1173 failing) and there have to be more of them out there in hackers hands somewhere (Yes, I have seen a few out there on the web like http://www.prc68.com but not many - and yes there has been discussion of them on the time-nuts list) . The other side of that is these were expensive pieces of equipment (don't know what the cost of a 4040A/RS new was but I have been curious to know) and I would assume most of them stayed in service until they ran out of cesium and were then disposed of because they were never going to work again. Another reason they might not end up on the surplus market that often is because cesium is a hazardous material and I assume many companies have policies about how to dispose of these kind of things due to various laws and regulations and such. Yes, there are plenty of different cesium standards for sale on ebay at any particular time but when you consider the world wide population vs how many of these units are for sale on the surplus market at any particular time you are really only talking about a tiny handful of devices. The vast majority of the cesium standards I have seen for sale are HP and the Datum/FTS ones are very much in the minority.

Still thinking about what to do with the 4040, I keep going back and forth on it. I want to do something fun with it but not quite sure what yet.

[edpalmer42]

The other side of that is these were expensive pieces of equipment (don't know what the cost of a 4040A/RS new was but I have been curious to know)

Check out this auction - particularly the last picture.  Oct. 2002 vintage, $24102. 

http://www.ebay.com/itm/FTS-4050-CESIUM-FREQUENCY-STANDARD-/331765084794

Ed

[hydrogen maser]

OK, so I think I have a general sort of plan now. Display to be mounted on the 4040: Mostly I know what I don't want for that at this point: something last looks chintzy. I want a proper industrial display and I am willing to pay more to get it. I think the best way to go is with a display that is as large as possible and is just that - a display only. There is not a lot of extra space inside the 4040 and I don't want to try to put a DC to DC converter in it and tap off the 4040 PS - I don't know how much margin there is in the 4040 PS so my plan is that everything is really external to the 4040. The only connection from the "4040" is the rs-232 and that is not really coming from the 4040, it is coming from the 5045A. Display on the front of 4040 with a hole drilled behind it - all wiring goes out the back and into another rackmount unit that has the computer for the display. That rackmount computer can be as sophisticated as necessary and have multiple video outputs, a larger one for detailed info and another one for the 4040 display. Not sure what to display on the 4040 yet, it likely will need a custom program for that. I may wish to mirror the rs-232 output from the 5045A into another system with multiple timebases on whatever bus I decide for that but I think the best way to go about this that has the largest chance for success is a modular system. I really need to rearrange my lab because I have outgrown it and have too many things stacked up so the rack mount system is something I have been thinking about for a while and it is just time to do that and get the counters and function gens and spectrum analyzer (TBD - 70000 HP looking like a nice option) mounted up and out of the way. So, a general plan is formed now.

[edpalmer42]

Sounds like an ambitious plan.  It'll be interesting to see how it develops.

Ed

[guido]

Got my hands on three (...) Datum PRS-45A units (2x Rev C and one J). Just powered up the first one (the J). Locked in some 20 minutes 
I already prepared a PC with Monitor3, that worked in one go. Lots of interesting numbers.

The J unit is from 2002, run time 33540 hours. That is only 3.8 years.  So it seems they did not run 24/7, or where switched off long ago. I know these units are not from a telco operator. I don't know how long they have been decommisioned. A piece of paper suggests 2007, but it is hard to read. Vacuum is good, the pump is now at 0uA after running for 1.5 hours. Got to 0 quickly.

Tube is a 7613A/077.

I see a Dallas RAM+battery. I'm wondering what data is present in there. Could be the log and the running hours. Need to look into replacing those (including copying of the data). I'll also backup the ROMs.

So which numbers are important? After one hour running:

• Clock servo Ramsey/Rabi errors are at some mVolts
• Zeeman Ramsey/Rabi are at -6 and -12. C field is 29mV
• Ion Pump is now at 0uA.

Empty alarm list (apart from one power supply that i did not connect).

Time to look at the other two...

[uncle_bob]

Hi

After a short run, vacuum and beam current are the two big things. Next on my list would be the EFC on the OCXO to see if it's drifted badly.

Bob

[guido]

Thanks.

Vacuum i presume is the Ion Pump current; stays at 0 uA.
Beam current I presume is C-Field (?), which is 18.90 mA, no idea at the moment if that is good or bad 
OCXO CV is stable at 3292mV

All of these seem stable for the 1.5 hours after warm up/lock.

[uncle_bob]

Hi

Vacuum is indeed the ion pump. OCXO at 3.3V is a bit high, but not worth doing anything about.

The C field is the magnetic field that the beam runs in. You "tune" the Cs by varying the C field. It's not worth digging into right now.

You should have a reading in there somewhere for the beam current. The beam is generated by "boiling" Cs off of a source inside the tube. As the source depletes, the current drops. Monitoring the current is one way to guess how much life a tube has left.

I'm an "HP Guy ( 5061's) " rather than a Datum owner. I can't help with the "where is the beam current in the menu?" question that obviously comes next. Of course if somebody sent me a couple of Datum's I *could* become a Datum guy 

Have Fun

Bob

[guido]

Looks like C-Field current is the beam current. The manual says that it gives an alarm >22 and <16V. Current in volts.. I assume it is a typo in the manual and it should say mA like the monitor software. So 19uA would be "half way", which somewhat matches with the run time.

Number two just locked.      I'll leave it running for 1.5 hours now.
OCXO at 2804mV, Ion Pump went up to 9uA (edit: probably much higher, but did not notice), but is now at 0. C-Field on this one is 19.1mA. Which would match the running hours, it's some 3.5 years on this one.

Also from 2002, but a Rev C. But same tube and same firmware.

[edpalmer42]

Congratulations on your score!  Don't bother buying any lottery tickets for the next lifetime or two - you've used up all your good luck! 

The only info I've got on the PRS-45A is some pictures, so take this info with a grain of salt.  The main signal strength is often called something like 'Ramsey Level', but Monitor3 doesn't use that term.  I think 'Clock Level' is the term it uses.  'Signal Variance' shows the noise level.  For a standard tube it should be < 200 or 225.  A high performance tube should be < 100.  As the tube ages, the value will slowly creep up and the Clock Level will drift down.  Eventually, the signal will become really noisy and the unit won't lock.

As Bob said, C-Field is a magnetic field used to fine-tune the frequency.  It has nothing to do with the signal level.

Take a look at this document.  http://www.ampere.com.mx/pdf/Manual_CsIII.pdf .  It gives some details about Monitor3 and the meaning of the terms and info.  Be careful about using any of the acceptable values since it's a different model.

I have no info on your tube or what an acceptable OCXO tuning voltage is, but 3V3 doesn't sound bad.

Ed

[guido]

And number three also locks without problem. This one is from 2001 and has some 3.9 years of run time.

Thanks for the document, i've got a lot of reading to do. When i search for "life" in the pdf, there are a number of parameters mentioned:

OCXO Control Voltage. Typical 2-4 VDC during lifetime. My values are 3.2, 2.8 and 3.0 after running for ~2 hours. So well within spec.

DAC Gain: 1.4 to 256, where 256 is end of useful life. My values are 3.88, 4.27 and 3.08. It's 256/N, where N varies from 180 to 0. So an N of 66, 60 and 83. "On" hours: 33540, 31071 and 34406. That does not add up, the one with the longest hours has the highest value. It would add up if N goes up, instead of down to 0. But you are right, this is for a different instrument. Maybe the value goes up here? I will see where it goes in the future.

Think the parameter for "Signal Variance" is Signal Deviation, or Deviation. 120-150 for a normal tube and 70-90 for a high performance tube it says in the doc.
I've got: 145, 141 and 147. But 120-150 is for the CsIII. You are mentioning 200/225, that's better And also the values went down during the hours they ran. E.g. from 200 after lock to 147. So it could well be going down further after more "on" time.

I found the loggin function in the monitor program. For number three i've made a logging for the whole time. You see the Ion Pump go up to 70uA, going down in the ~25 minutes it takes time to lock. When it locks the OCXO jumps to the control voltage and then slowly creeps down again (further warm up of the oven).

Unfortunately there are no such details in the PRS45 manual. And i did not find a manual for the PRS45A at all.

Some pictures:


The alarm is because there is only one power supply connection used (Fuse A open). No other alarms.









Yes it was a score. I payed peanuts for all three...

[notfaded1]

Dragging up this necro'd thread.  I hope some of you guys are still around?  I picked up an FTS Datum 4040A that's on it's way to me now.  I'm not sure what to expect being 20 years old though.  The pics make it look like it's been taken care of.  It was bought in a "freight auction" I'm not sure what that means?  When I get it what should I check?  Does anyone have the manual for this?  Many of the links in this thread were dead.  I did find the manual for the MODEL 4065C and it refers to the 4040A.  Here are some of the original pics.  I've always wanted one of these so I pulled the trigger... I figure it's worth a try right?  I did manage to download monitor.zip which is good.

Bill

[notfaded1]

I found a document that explains the difference between the 4040A and 4040A/RS... thankfully mines an RS which (it makes sense) is a reference to the serial RS-232 monitoring functionality.  This is a relief because reading here I was afraid I might not be able to interface directly to the clock at first.  I also found the original specs page for the clock.  I couldn't find a manual specific to 4040A/RS but the MODEL 4065C manual references it and I'm hoping the interface and commands are mostly similar.  I attached it here as well.  It seems to continue this previous thread made sense so all the information is here in one place.  I'm hoping after I start working on this that others might comment and potentially assist.


Bill

[edpalmer42]

Did you find this thread?  https://www.eevblog.com/forum/metrology/datum-fts-4040a/

When you get your unit, you'll be able to find out what's inside.  If it turns out to be the 5045A version you'll be able to talk to it via RS-232 using Monitor, or preferably, Monitor3 http://www.w2hx.com/x/Datum/PRS45A/Monitor3.zip .  Otherwise, it looks like there's not much in the way of monitoring/diagnostic.

Obvious first steps are to check for bad caps, power supply voltages, OCXO frequency & EFC, obvious burned/broken parts, loose ground connections, etc.  If you've got a high voltage probe and you're feeling brave you can check the high voltage supplies - carefully.

Be sure to read this entire thread.  There are many nuggets of info sprinkled through it.  For example, the manual for the 4040B at http://www.mediafire.com/download/6icdc7v35c68t16/4040B_mnl.pdf , failure modes, internal power supply voltages, etc.

What other measuring equipment and reference sources do you have?

Ed

[notfaded1]

Thanks so much for the response Ed.  I've been reading all of your posts on the threads about this.  Ironically my only other references are Symmetricom Syncservers S200's.  One has the x72 rubidium oscillator in it.  I have a scope, MM's and collection of old counters.  I really need another separate reference.  I've been reading about the software (thanks for posting the monitor3 btw... I've been looking for it all day and just sent a PM to EMUD asking him about it since all I could find was the original monitor.exe DOS program.  I'm just hoping that there's cesium left in the tube.  The serial number is 02013.  From what I can see it does say 4040A/RS on the front so I'm really hoping it's able to talk through the 25 pin female RS-232 port on the back.  I noticed in many other pictures it's a male connector but I suppose that doesn't mean much... just something I noticed.  It looks like it may require a null modem as well since the manuals say it's DTE to DTE in the diagram when hooking to a PC serial port.  I'll open it up and take pictures as soon as it gets here to AZ from UT.  It's being sent by UPS ground.  It must not be light... I could see in the manual for your unit it lists around 75lbs. if I'm not mistaken.  I've got a good known working USB to 9 PIN serial cable I use for the symmetricom units that should work well with an added 9pin to 25 pin serial converter and maybe null modem.  Oh and Happy almost New Year 2020!  History wise the seller said he acquired the unit in a freight auction and didn't have a use for it so was selling it.  The anticipation is killing me... I know it powers up and he said he only plugged it in just to see if it would turn on.  Fingers crossed!

Bill

[hydrogen maser]

Mine is also the 4040A/RS - it is silk screened as just "4040A" on the front but the label on the back says 4040A/RS and you do need a null modem cable to talk to it over serial. I got this cable from Amazon (I have db9 serial ports on the computer) and it works on mine: https://www.amazon.com/gp/product/B000I1EXT0/  monitor3 is the way to go if you can because monitor.exe only works in dos box on windows 7 (Win8/10 ) and you have to fiddle with a serial configuration file to get it to work but monitor3 just works - much easier. If yours is like mine monitor3 will misidentify your unit as being a different model and the log function will not work but otherwise it is much better than monitor.exe. Kind of on the fence as to - just fire it up and see what happens vs tear it apart and see if you have bad caps in the dc to dc converter in the 5045a like mine did - your call. BTW mine still works, I turn it on every 6 months and let it run until the pump current goes to zero. 

[edpalmer42]

Thanks so much for the response Ed.  I've been reading all of your posts on the threads about this.  Ironically my only other references are Symmetricom Syncservers S200's.  One has the x72 rubidium oscillator in it.

I'm not familiar with the Syncserver.  A quick browse through the datasheet didn't show any 10 MHz or 1 PPS outputs.  Are either available either externally or internally?

I have a scope, MM's and collection of old counters.  I really need another separate reference.

The scope will get you started.  If you can pull data out of one of the counters, that will be the next step.  You may have to improvise by using either the 4040A or the Syncserver as the reference for your counter while you measure the frequency of the other.  Not ideal, but you use what you've got.  Ideally, you use a Time Interval Counter to measure the time between the rising edges of the 1 PPS output from your reference and the DUT and collect the data on a computer.  The outputs won't (and *can't*) be in phase, but if the difference is constant, the frequencies are identical.

I'll open it up and take pictures as soon as it gets here to AZ from UT.  It's being sent by UPS ground.  It must not be light... I could see in the manual for your unit it lists around 75lbs. if I'm not mistaken.

Yes, it's a beast.  The UPS guy who delivered mine looked like Arnold Schwarzenegger!  Be sure to check it carefully for damage, both internal and external.  There's a good chance it will have been dropped - at least once! 

Remember that when you first power it up it'll have to pump down the tube before much else happens.  I'd recommend that you hook up the RS-232 right away, if possible, so that you can monitor the process.  The most important number initially is the ion pump current.

[CJay]

Threadjacking but I'm still in need of some info about the DC-DC converter in my Datum Cs standard, does anyone have one of these tand would be willing to check some things for me please?

I've a few pads/tracks damaged by the capacitor leakage and a diode that's got the cathode floating, it looks to have burned up in the past and been replaces but whoever did it seems to have pulled the thru hole plating out so there's no connection to the cathode.

[notfaded1]

I have a tracking number and the shipping details says:  Weight 50.40 LBS.  It says it'll be delivered by Friday so fingers crossed.  It's one of those label created tracking messages though so who knows if it's really moving yet?  Thanks for the tip on the null modem cable HM...  weird that mine has female DB25... not that it really matters but most pics of units I've seen it's male.

I'm guessing that some of my counters that have A, B, and C inputs that looking at an A/B ratio might tell something to compare a one source to another but I know that generally frequency counters and interval counters aren't the same but are similar and use similar components.  For used the HP5370A and B models look pretty good?  Wow some counters specifically called time interval counters can get expensive too!  The SRS SR620 look like the more recent cadillac of TIC's!  I've always been somewhat of a voltnut but now I've really got bitten by the timenut bug... in my day job we do a lot to support the brand new Block III GPS satellite constellation so it just makes sense to have an interest in this and time in general.

I'm thinking it'll be normal to have a bunch of alarms on unit until the tube pumps down?  I've read (by you guys) it can take even days to pump down if it's been sitting for a long time?  Geesh I still can't believe it's 2020 already o.O!  Here's to hoping I can track 2020 with precision I didn't have in 2019!

Best Regards,

Bill

[edpalmer42]

I'm guessing that some of my counters that have A, B, and C inputs that looking at an A/B ratio might tell something to compare a one source to another but I know that generally frequency counters and interval counters aren't the same but are similar and use similar components.  For used the HP5370A and B models look pretty good?  Wow some counters specifically called time interval counters can get expensive too!  The SRS SR620 look like the more recent cadillac of TIC's!  I've always been somewhat of a voltnut but now I've really got bitten by the timenut bug... in my day job we do a lot to support the brand new Block III GPS satellite constellation so it just makes sense to have an interest in this and time in general.

If your counter has A and B channels, it probably has a Time Interval mode.  Good counters can be pricey, but you can use almost any counter at this point so don't rush out and buy one yet.  A good start would be a counter that has a minimum resolution of 1 ns. like the Racal Dana 1991/1992 or Agilent 53131.  Many of the Racal units have bad buttons so move carefully.  An economical alternative is the TAPR TICC.  The SR620 is one of the best available.  The 5370B is close behind.  I have a Fluke PM6681 which is an OEM version of a Pendulum counter.  Tektronix also makes some high end counters.  If you want something big and heavy enough to compete with your 4040A, you could even get a Wavecrest DTS unit.  Warning:  it's weird and it's LOUD, but it does have potential to be the best of the bunch.  Mine has an ADEV noise floor of about 5e-12@1 sec.  You can even sort of use it as a digital scope with 100 Gsps equivalent sampling!  Don't buy one without talking with me.  All of these units are available on the auction site we love to hate.

What counters do you have access to?

I'm thinking it'll be normal to have a bunch of alarms on unit until the tube pumps down?  I've read (by you guys) it can take even days to pump down if it's been sitting for a long time?  Geesh I still can't believe it's 2020 already o.O!  Here's to hoping I can track 2020 with precision I didn't have in 2019!

My 4065A always starts with an alarm that just tells you that it restarted (in case there was a power failure).  Depending on the state of your tube, it could take many, many days to pump down the tube.  I just dug mine out.  I didn't realize that it had been so long since I ran it.  After sitting idle for 30 months, the Ion Pump current peaked at only 101 ua and by the time the unit locked (about 10 min.) the current was zero.

I was watching the startup behaviour very carefully and learned something new.  The first thing that happens is the OCXO warms up and changes from a COLD state to a WARM state.  That takes about 10 minutes.  Once that happens, the Ion Pump and Cesium oven start up.  About ten minutes after that, the unit locks.  If you're monitoring the output frequency, you can see it rise slowly to within a few Hz of 10 MHz, then stall for a while, and finally swing above and below 10 MHz before it locks.  So total time from power-on to lock was about 20 minutes.

Always remember the first rule of Cs standards.  Don't run it unless you need to.  It has a limited amount of Cesium and whenever it's running, you're using up that supply.  Once that's gone, the unit is junk.  There's no way to find out how much Cesium is left in your tube.  Some (most?) newer units have runtime counters, but that still doesn't tell you how much is left.

[notfaded1]

I have many counters (I especially collect nixie tube counters) but since you mentioned it I have a Racal Dana 1991... it's kinda strange on it's own because it has a 1992 body with 3 inputs on it but inside it actually only has 2... it does have the OCXO inside the back corner which I think was an option?  When it boots up it says 1991 not 1992 like the outside markings say.  I thought about giving the guy that sold it to me bad feedback but I don't think he really knew and I got it cheap.  I'm pretty sure it'll work like a 1991.  Oh and yeah I know about the buttons on the Racal's... mine are ok.  I actually did get some replacement buttons I was going to install on it but I think mine are good enough that it works at least now.  I actually bought a HAKKO FR-301 desoldering gun just for the job because its a LOT of buttons and a LOT of connectors!

Regards,

Bill

[edpalmer42]

Threadjacking but I'm still in need of some info about the DC-DC converter in my Datum Cs standard, does anyone have one of these tand would be willing to check some things for me please?

I've a few pads/tracks damaged by the capacitor leakage and a diode that's got the cathode floating, it looks to have burned up in the past and been replaces but whoever did it seems to have pulled the thru hole plating out so there's no connection to the cathode.

A model number and a picture or two would be helpful.

[notfaded1]

Just got the 4040A out of huge box and cleared enough space to put this monster.  I haven't opened it up yet maybe tomorrow but I wanted to plug it in at least and see what happened.  I did hook up the RS-232 at 2400 7 2 Odd with null modem cable and didn't see anything on putty at all.  I'm wondering if I should wait a while and see what happens or?  I had to hook up the Racal Dana 1991 though and at least look at the 10MHz output.  Attached is the picture.  When I plug it in I hear a brief click then that's really it and you see the lights on right now.  I kinda expected it wasn't going to just lock up in under 30 minutes.  The align/initialization and operation alarm/fatal alarm indicators are LEDs and buttons.  I'm guessing it's been sitting a while.  Weird thing on the back the storage/operation switch isn't there it has a blank in the space.  I'll take more pics tomorrow.  I guess leaving it on for now won't hurt anything.

Bill

[notfaded1]

Here's that normal storage where switch is on some units.

Bill

[notfaded1]

And the BNC that that are on it...

[edpalmer42]

Just got the 4040A out of huge box and cleared enough space to put this monster.  I haven't opened it up yet maybe tomorrow but I wanted to plug it in at least and see what happened.  I did hook up the RS-232 at 2400 7 2 Odd with null modem cable and didn't see anything on putty at all.  I'm wondering if I should wait a while and see what happens or?

Until you open it up, you don't know if the guts are smart or dumb.  If smart, run Monitor3.  It might not speak until you ask it nicely. 

I had to hook up the Racal Dana 1991 though and at least look at the 10MHz output.  Attached is the picture.  When I plug it in I hear a brief click then that's really it and you see the lights on right now.  I kinda expected it wasn't going to just lock up in under 30 minutes.  The align/initialization and operation alarm/fatal alarm indicators are LEDs and buttons.  I'm guessing it's been sitting a while.  Weird thing on the back the storage/operation switch isn't there it has a blank in the space.  I'll take more pics tomorrow.  I guess leaving it on for now won't hurt anything.

I wouldn't leave it on overnight.  I'd open it up, do an inspection, make some measurements on power supplies, etc., and  babysit it for a few days.  Then, once I had some confidence that it wasn't going to burst into flames, I'd consider leaving it on overnight.  Of course, if any of my inspection/testing showed anything even a bit twitchy, I wouldn't run it without supervision.

Ed

[notfaded1]

Ok here goes opening up the top first.  My camera crates such high res photos that I can only fit one on a post so bear with me.  You should be able to zoom in a lot but I'll take some closer pics too.  I know know why the DB-25 did nothing before.

Bill

[notfaded1]

The back of the DB-25...

[notfaded1]

This is where power connects in.

[notfaded1]

There's a lot going on in here... Multiple PCBs.

[notfaded1]

There is a modular build to it... Pieces fit together tightly in the space.

[notfaded1]

This big cable bundle that runs to the back connections has some unpopulated connections on it.

[notfaded1]

Flipping over to the tube side.

[notfaded1]

Beam tube model number FTS-7503

[notfaded1]

The LO is the Datum 1000B:
http://www.leapsecond.com/museum/datum-1000b/

[notfaded1]

I wish there were service manuals... They'd rather have you call the number stuck everywhere... Back of the beam tube in the middle.

[notfaded1]

Some caps tucked in next to the beam tube.

[notfaded1]

Ed I found a picture of the FTS-6006 monitoring module... Found this while researching this unit.  I think Arthur Dent from time-nuts was selling them for $150 long ago... It looks like it adds some of the features your unit has to a 5030A maybe... I'm not sure how you connect it though... This stuff is just old enough that there's not a lot of manuals anywhere online for much of it.

A lot of mine is similar to the unit here: http://www.prc68.com/I/FTS4060.shtml

I think I've got work to do... Worst case this things got an awesome crystal occillator in it.  The link above goes into testing one of the them.

Bill

[edpalmer42]

Hey, no fair!  Stop editing your posts while I'm writing mine! 

It looks like you've got the same unit that was discussed here:

https://www.eevblog.com/forum/metrology/datum-fts-4040a/?all

There's almost no info available online so you're kind of on your own.  I'd probably see what I could discover on the monitor connector.  The 4040B only has contact closures, but the 4040A might have a couple of DC levels like the FTS 4050 or 4060 (See attached pictures).  I don't see how they could provide nothing at all.

I don't know if tkamiya discovered anything more.  Maybe PM him if he doesn't jump in here.

As for measuring it, you need to dig a signal out of your Syncserver.  It doesn't matter if it's 1 PPS or 10 MHz or anything in between - within reason!  A square wave is preferred, but use a sine wave if you have to.  Warm up your 1991 and, if the frequencies are different, connect Input A to the lower frequency signal and Input B to the higher frequency.  Start taking measurements of the time-of-day and the delay between the two.  Expect some wandering initially as everything warms up and settles down.  Noise will also cause wobbles, particularly if you're using any sine waves.  Generate a graph from the data and see what you see.

Ideally, the value will stay constant except for some noise.  Likely, there will be a tiny frequency offset.  I think my 4065A was off by < 1e-12.  But is that real or did I not measure long enough?  Random noise could look like a frequency drift if it happens to nudge things in the same direction for a little while, but then it turns around and nudges things in the other direction and your so-called drift disappears.  Anything more than this (i.e. Allan Deviation) requires automated data collection.

The 6006 module is very interesting.  I see that Arthur Dent was selling one on Time-Nuts last Nov.  He said that it worked with the FTS 5030 which is what you've got.  He's here on eevblog, if it's the same Arthur Dent.  If the module isn't available now, you should really consider reverse-engineering that monitor connector.

Ed

[notfaded1]

Thanks Ed for the help.  I just got notice my FA-2 was delivered and I also got delivered today this dist amp with another nice built in OCXO:
https://www.ebay.com/itm/LMT-10-MHz-Oven-Oscillator-Time-Base-W-11-Out-Dist-Amp/143496912125

Looks pretty good and I'll solder in the additional inputs and outputs to also convert my S200 to an S250 syncserver (need to figure out how to drill the holes on the back out... I have the parts already).  I just got a new Dell XPS tower and ultrasharp monitor to build a better lab machine for monitoring.  Lots to do now!  I can't wait to see ladyheather and other tools running on there sampling with my counters over GPIB.  Any windows software you recommend for the data sampling over GPIB?  Andreas here hooked me up with Linux image for my raspberry pi but I really want to also use Windows 10 for some of this in my lab too.  My GPIB is a Keysight USB.  Where I work they use test stand and labview but I really like free open source software... The price is right.  I'd rather spend more money on gear 

I too was wondering if it's the same arthur dent?

Bill

[notfaded1]

I'm also a little unsure on testing the HV.  All I have is an HP34401a, fluke 87V and 289???  I usually like in the link keep my hands away from voltages like that... Well my nixie tubes PS don't generate much current and it's less than 200V... I'm guessing the CS tube PS has some more current than what I'm used to.

Bill

[edpalmer42]

Thanks Ed for the help.  I just got notice my FA-2 was delivered and I also got delivered today this dist amp with another nice built in OCXO:
https://www.ebay.com/itm/LMT-10-MHz-Oven-Oscillator-Time-Base-W-11-Out-Dist-Amp/143496912125

I don't have an FA-2, but based on the info in the message thread, it looks interesting.

The distribution amp looks good.  It looks like most of the outputs have two jacks connected to the same output.  At the levels of precision you could be reaching, there might be feedback between two devices connected to the same output.  That would show up as strange wiggles in the graphs.  If you see anything like that, make sure to plug the devices into separate outputs.

I just got a new Dell XPS tower and ultrasharp monitor to build a better lab machine for monitoring.  Lots to do now!  I can't wait to see ladyheather and other tools running on there sampling with my counters over GPIB.  Any windows software you recommend for the data sampling over GPIB?  Andreas here hooked me up with Linux image for my raspberry pi but I really want to also use Windows 10 for some of this in my lab too.  My GPIB is a Keysight USB.  Where I work they use test stand and labview but I really like free open source software... The price is right.  I'd rather spend more money on gear 

Depending on your programming abilities and what software supports what hardware, there are LH as you've mentioned, Timelab, the new free community version of Labview, PyVisa that works with Python, and EZGPIB which is a free Pascal-like interpreter with extensive GPIB add-ons.  I'm sure I'm forgetting many more.

I'm also a little unsure on testing the HV.  All I have is an HP34401a, fluke 87V and 289???  I usually like in the link keep my hands away from voltages like that... Well my nixie tubes PS don't generate much current and it's less than 200V... I'm guessing the CS tube PS has some more current than what I'm used to.

The high voltages on mine are +3300 V and -2600 V so if you don't have a high voltage probe or the knowledge to safely build/use one, let that pass for now.

You haven't said what's actually happening with the unit.  Did your inspection show anything bad?  Any bad electrolytic or Tantalum capacitors?  Screws all tightened?  Voltages seem reasonable as far as you know?  Does it pass the sniff test?

And most important, does the lock light come on???

Ed

Edit:  corrected typo - changed +33300V to +3300V

[notfaded1]

No lock yet.  All the screws are tight I don't think anyone has ever opened it before it isn't even that dusty despite having some air holes on both sides.  I've got work to do testing caps, probing the monitor port, and carefully checking voltages on boards.  I think if I use my scope for some I'm going to plug the Datum into my isoMATE so I don't have to worry about ground loops.  Without good documentation it's a little more scary.

On another note my new FA-2 feeding it's 10MHtz back into itself it's better than some that posted here I think.

Bill

[notfaded1]

Ed-
You're right I wasn't thinking about the message really I had been IM'ing with CJay asking him about the caps he changed.  There are a TON of tantalum caps on the main board o.O!  It's hard to read all the values too... I don't see any big cap problems yet.  I may need to take the cage off the PS in the back to be sure though (that's where the big electrolytics are).  I don't see any major issues yet though.  There are some test pins on the boards though and that link helps comparing to similar unit.

Bill

[ArthurDent]

Ed I found a picture of the FTS-6006 monitoring module... Found this while researching this unit.  I think Arthur Dent from time-nuts was selling them for $150 long ago... It looks like it adds some of the features your unit has to a 5030A maybe... I'm not sure how you connect it though... This stuff is just old enough that there's not a lot of manuals anywhere online for much of it.

A lot of mine is similar to the unit here: http://www.prc68.com/I/FTS4060.shtml

I think I've got work to do... Worst case this things got an awesome crystal occillator in it.  The link above goes into testing one of the them.

Bill

I did sell one of the FTS 6006 controls a few years and have at least one left. The interface cable is about a 37 pin straight through cable as shown in the photo below. 

[Teti]

Sorry for OT.
I've been snooping around Caesium Frequency Standards today and found this on FleaBay: eBay auction: #112745451687.
It appears to be locking according to seller's pictures. Any thoughts about the price, model etc.?
At the moment out of my financial reach. Perhaps chip scale Caesium frequency standards would be better standalone option?

[notfaded1]

Ed-

Still working on the 4040a.  I printed out all the docs I have and I'm digging further into the individual pieces.  I did acquire something to help with testing and it locked up in under 10 minutes!  See attachment.
  I've got another rubidium standard too I'll post about them both on separate new thread focused more on rubidium.  Despite this cesium not having a modern serial interface it sure is nicely built.  I need to know it's good or not so I'm going to invest more time in it.  Now with two additional rubidium standards I'll have more to compare to it.  I also have an HP 53131A with the third channel coming to also use for comparisons.  My new computer I'm going to load up labview 2020 on to make comparisons.

Bill

[edpalmer42]

Sorry for OT.
I've been snooping around Caesium Frequency Standards today and found this on FleaBay: eBay auction: #112745451687.
It appears to be locking according to seller's pictures. Any thoughts about the price, model etc.?

The fact that it locks is, indeed, promising.  But, like all Cesium standards, there's no way to determine how much life is left in the tube except maybe for the last few gasps of a dying tube.  If I was paying that kind of money, I'd ask for more info on the unit.  The vendor would have to connect up a serial cable, install and run the software, and then send you the results.  Expect a lot of pushback.  A link to the manual was posted somewhere in this thread.  By looking through that, you can get an idea of what to look for.

As for the price, that's something you'll have to decide for yourself based on your needs, budget, and the age of the unit.  I don't have enough experience to comment on whether the price is reasonable.  I'm only interested in unreasonable prices.   

At the moment out of my financial reach. Perhaps chip scale Caesium frequency standards would be better standalone option?

Don't get confused with the 'Caesium' part of that name.  The chip scale Caesium units are not comparable to the type of Cesium standard we're discussing in this thread.  It's operation and performance is comparable to a Rubidium frequency standard, i.e. it drifts.

Ed

[edpalmer42]

Ed-

Still working on the 4040a.  I printed out all the docs I have and I'm digging further into the individual pieces.  I did acquire something to help with testing and it locked up in under 10 minutes!  See attachment.

You had me going for a second, there.  I thought you said you bought something that helped the 4040A to lock up in 10 minutes!     Oh ...... wait ..... 

  I've got another rubidium standard too I'll post about them both on separate new thread focused more on rubidium.  Despite this cesium not having a modern serial interface it sure is nicely built.  I need to know it's good or not so I'm going to invest more time in it.

Exactly!  I was in the same position and that's when I decided to measure the tube response since that's the most likely failure.  Since the results looked good, I carried on and found that my unit had a well-known electronic failure mode, but I had to find an obscure chip to fix it.

Now with two additional rubidium standards I'll have more to compare to it.  I also have an HP 53131A with the third channel coming to also use for comparisons.  My new computer I'm going to load up labview 2020 on to make comparisons.

Until you get it to lock, there's really nothing to compare.  You'll see the output frequency wander around near 10 MHz.  It might not even go above and below 10 MHz, it could be on either side.

Flying blind without even an operating manual makes things quite challenging.  Older Cesium standards are more or less PLL systems.  My 4065C is way too smart and jumps the frequency to something like 14 discrete frequencies to check for proper tuning and measure the state of the tube.  We don't know what yours does.

To test the RF path, you need to be able to measure 9.192631770 GHz with a resolution of at least 10 Hz, preferably 1 Hz and a similar absolute accuracy.  So, you probably need either another Cesium standard or, more likely, a GPSDO or access to a similar frequency source.

To test the tube itself, you need to be able to measure the DC signal coming out of the tube.  For my tube, it was about 10 na into a 100Mohm load.  You also need to be able to step the input frequency in 10, preferably 1 Hz increments.  For my unit, these steps were at around 12.6 MHz, yours might be different.

Of course, reverse engineering that monitor connector will probably help, but it will be tricky to interpret the outputs without any documentation.

All in all, a challenging project!

Ed

[Teti]

Sorry for OT.
I've been snooping around Caesium Frequency Standards today and found this on FleaBay: eBay auction: #112745451687.
It appears to be locking according to seller's pictures. Any thoughts about the price, model etc.?

The fact that it locks is, indeed, promising.  But, like all Cesium standards, there's no way to determine how much life is left in the tube except maybe for the last few gasps of a dying tube.  If I was paying that kind of money, I'd ask for more info on the unit.  The vendor would have to connect up a serial cable, install and run the software, and then send you the results.  Expect a lot of pushback.  A link to the manual was posted somewhere in this thread.  By looking through that, you can get an idea of what to look for.

As for the price, that's something you'll have to decide for yourself based on your needs, budget, and the age of the unit.  I don't have enough experience to comment on whether the price is reasonable.  I'm only interested in unreasonable prices.   

At the moment out of my financial reach. Perhaps chip scale Caesium frequency standards would be better standalone option?

Don't get confused with the 'Caesium' part of that name.  The chip scale Caesium units are not comparable to the type of Cesium standard we're discussing in this thread.  It's operation and performance is comparable to a Rubidium frequency standard, i.e. it drifts.

Ed

Oh I haven't put much research into it. Just the the name Atomic clock sounds like a scam I don't think they last that long  as according to wiki: MEMS techniques were used to create a cesium capsule only 2 cubic millimeters in size. Units cost about $1500 for Rb and $3000 for Cs standard. Cost of new 5071A from Microsemi is about $30k.
Looks like I'll have do with my FE-5680 + GPSDO for now and keep wet dreaming.

I don't think majority of us need Caesium standard unless being diagnosed time nuts

[notfaded1]

Ed-

Isn't it just measuring the 1000B ocxo when it's not locked?  It's a really nice ocxo but that's not the same as all as locked in stability.

I picked up another strange symmetricom GPS unit too called a Mark V.  Attached some pics I'm trying to get it to GPS lock.  It's got more outputs on it... Multiple 10MHz.

Bill

[edpalmer42]

Ed-

Isn't it just measuring the 1000B ocxo when it's not locked?  It's a really nice ocxo but that's not the same as all as locked in stability.

When it's not locked, the system will be pulling the frequency here and there trying to find the Cesium signal.  Under those conditions, ADEV will be horrible at low values of Tau and drift will be high at larger values of Tau.  The 1000B by itself should give good results, but you'd have to seperate it from the 4040A and put it in a box by itself with a stable EFC voltage.  Then keep it powered up for a month or two to let it settle down.

I picked up another strange symmetricom GPS unit too called a Mark V.  Attached some pics I'm trying to get it to GPS lock.  It's got more outputs on it... Multiple 10MHz.

Be careful with that.  Some old GPS receivers fed 12V up to the antenna.  Connect one of those to a modern antenna and you'd instantly fry it.  Other old units required a downconverter between the antenna and the main unit.  Without the downconverter, the main unit is deaf and blind.

Ed

[5065AGuru]

Hi,

Should be +3300V not +33300V!!!

"The high voltages on mine are +33300 V and -2600 V so if you don't have a high voltage probe or the knowledge to safely build/use one, let that pass for now."

Cheers,

Corby

[notfaded1]

Ed-

Good warning on the antenna!  I've got a 12V Symmetricom antenna because I have all those syncservers that require it.  I had to convert from TNC (on the antenna and cable) to BNC for the symmetricom units.  It's much harder than most people realize to get a good 12V GPS antenna... that's a rookie mistake right there connecting one of those 3.3V or 5V antenna to one of these... it'll definitely blue smoke it!  I recently got a Symmetricom 58535A GPS Active 3-Way Splitter as well and am going to set it up as soon as I make all the cable conversions... I think I want to order real converters for it versus using my conversion kits I have to make them.  I scored a really nice Pamona RF conversion kit... my previous one was a cheaper Impact Acoustics RF kit.  I think the Pamona 5698 is a little nicer quality for RF conversion.  I've always thought these might have a little more insertion loss than a specific made connector although I'm not sure what difference it would make?  I've always tried to minimize insertion loss... we are voltnuts after all right?

Also on the Symmetricom Mark V it shows the antenna as good but I'm not picking up SAT's... I can't find docs for this unit either.  I'm wondering if I either need an unclassified key for this to work or possibly I should try attaching  my L1/L2 survey antenna instead of just my 12V Symmetricom L1 antenna.  SAASM is new to me.  I'm familiar with the keyfill port on the front but I'm not going get any keys for it.  I may try letting it run with an L1/L2 antenna to see... I didn't leave it very long attached to my L1 antenna and it didn't pick up any SAT's.  I was hoping it would work without being keyed... I may be out of luck with it.  It sure has some nice add on boards in it!  That would be shame!

Bill

[notfaded1]

Hi,

Should be +3300V not +33300V!!!

"The high voltages on mine are +33300 V and -2600 V so if you don't have a high voltage probe or the knowledge to safely build/use one, let that pass for now."

Cheers,

Corby

Thanks for this Corby... I was under the assumption that I needed a probe that could go over 30kV.  Without good docs troubleshooting this 4040A has been a challenge and I'm being careful.  I do know the PCB upside down in the front left corner of my unit is the HV supply which Brooke showed taken apart here attached.  I really should document what I'm going through to help someone as Brooke's site has helped me because it's NOT obvious at all.  His 4060 contains a 5030 that's identical to the 5030 in my 4040A.

So a Fluke 80k-6 (6kV or similar range) would work and I don't need a Fluke 80k-40 (40kV) probe for this to work then?

Bill

[notfaded1]

I found an interesting slide comparing some DATUM standards... it's older so the prices are probably not current obviously because it changed to Symmetricom and now microsemi since.  Just goes to show if you can get one of these working it's a nice kit to have!

Bill

[edpalmer42]

Hi,

Should be +3300V not +33300V!!!

"The high voltages on mine are +33300 V and -2600 V so if you don't have a high voltage probe or the knowledge to safely build/use one, let that pass for now."

Cheers,

Corby

Correct!  I've edited the original message to correct the typo.  Wow, 33 KV would get your attention, wouldn't it?   

Sorry for the error.

Ed

[5065AGuru]

Bill,

No need to use a HV divider, it's built in!

Attached is a page of the U1 IC monitor pins.

You can measure lots of bits there!

Cheers,

Corby

[jschatzman]

More data on a Datum 4065A.  Per Ed's data above, I replaced all 15 electrolytics on the cesium module power board. At least 3  of them were leaking (C3, C19, CH) and one was an open circuit. Per Ed's terminology:

C3,4 - was 120uf/100V replaced with 391uf/100V
C18,A,B,J - was 1000uf/15V replaced with 2200uf/35V
C19,20,C,D,E,F,G,H,I - was 220uf/50V replaced with 680uf/80V

Fortunately modern Nichicon long life caps are smaller than the originals for higher capacitance/voltage so finding replacements is easy.
Had little difficulty replacing the capacitors except that 2 were cemented down pretty well. All voltages now appear to be fine.

Unfortunately, that does did not fix the unit. It fails to lock up, displays a "major alarm", and CS error codes 2,3,5,7,8,18.

2 = voltage difference clock pedestal
3 = voltage difference zeeman pedestal
5 = C-field current <17mA or >20 mA (but frt panel reading is 18.6!)
7 = DAC voltage out of range
8 = oscillator control voltage
18 = beam gain DAC near limit

It does sweep the 5 MHz OCXO but doesn't seem to find a lock. So either the Cs tube is dead or there is some other problem.  I will read through Ed's notes above again and see if I can find any clues.

[edpalmer42]

Hi Jim,

Welcome to the group - although I see you've been lurking for a while.  Jim & I have been swapping emails about this unit.  I'm happy to discuss it here so that others can hopefully benefit from our conversation.  There's so little info available on these units that everything is useful!

All those errors are meaningless until the unit locks.  Just for completeness, I'll repost my troubleshooting list from our emails - with revisions.

1.   Power Supplies - check for voltage & ripple on all the power supplies, power bricks, modules, etc.  Nothing else works right until this is done.  I had trouble with the control panel until I found a couple of bad solder joints on the power bricks that are bolted to the right side panel.  My 4065A is down right now because some of the capacitors have gone bad.

2.  OCXO - on frequency or, at least, within tuning range of 10 MHz?  Yours might be okay, but since you did get an OCXO tuning alarm, that might be worth a second look later on.  It could just be a false alarm.

3.  STEL-1173 (U51 on the main board) - known to fail, hard to find, discontinued long ago, no second source.     I discussed testing it earlier in this thread.  Basically probe the output pins with a scope.  You don't have to trigger on them, just make sure that they're all toggling.

4.  Ion Pump.  The ion pump reading has to be low before anything can happen.  The 4065A seems to have a 'storage mode' where everything is shut down except the ion pump.  I say 'seems' because mine doesn't appear to work in storage mode.  If your ion pump reading is high and your pump works in storage mode, you can just plug the unit in and let it sit for a week or three and see if the current comes down.  I've seen values as high as 140ua, but it rather quickly pumped down to zero.  To monitor the pump current when the unit is turned off, i.e. in storage mode, measure the DC voltage between ground and the 'I Pump' pin on the ion pump high voltage power supply.  It's the supply that has four small terminals.  Mine are clearly marked.  You read the voltage and translate it to current like this:  1 mv = 1 ua .  So you should read something less than 240 mv.  If the unit is turned on, the ion pump reading is on the 'Status 3' display page.

5.  Test the Cs tube.  A high level overview of the test is in this thread (along with a few more info nuggets):
     https://www.eevblog.com/forum/metrology/datum-4040a-problems/ .  If you decide to, and have the equipment to do that, it's a bit of a project in itself.

Ed