HP 140T calibration

[factory]

Well, never thought I would end up doing this.
I ended up taking almost everything apart. Finally I had enough and I thought that if the potentiometer won't go farther, I will make it go farther. R470 is a resistor that is right before the regulating potentiometer. It's value is only 4320 , I grabbed a similar resistor that was 5.9K and swapped the two. I could now regulate it to where I wanted it and I got all the other lines to where they needed to be. No problem anywhere. I plugged in the units and the fuses have not been blowing anymore (crossing fingers). I forgot to mention that they where blowing. I did not find anything odd after some testing. Is this a band-aid, or a real solution? I think it's fine now.

Also the fan was not turning very fast at all. (maybe 2 RPM). Taking it out was a pain! Really! I oiled the shaft after a disassembly and now it's blowing enough air that I can feel it on the side vents.

Anything else I should look for. Right now it looks really nice with everything setup

Good to hear you got it all working, it may be you've compensated for something has drifted slighty out of spec in the power supply.
 
Here is the power supply board in my 140B, I think it may be the same type as yours, I will have to check the no-load voltage next time I use it (it's currently at the bottom of a stack of equipment), I've never done that before as I have plenty of the required scope plug-ins listed in the manual.

David

[Floopy]

Thanks for all the help. That board looks almost exactly like mine with two differences. #1 the components are a bit different (that's expected) and #2 I don't have an ENIG plated board.
You've been a great help!

I just need to figure out how to use all the functions now  .

I'm still looking for a solution to the crack in the frame, but the essential is working. In total it cost me 140$, I think it's a good deal for a unit like this.

[factory]

I'm still looking for a solution to the crack in the frame, but the essential is working. In total it cost me 140$, I think it's a good deal for a unit like this.

Have a look at this thread for a possible solution to the cracked frame;
https://www.eevblog.com/forum/testgear/hewlett-packard-740b-dc-standard-digital-voltmeter-(and-740a)/msg1419955/#msg1419955

It's something I will be looking at doing since I have a lot of HP delivery victims here too. 

David

[Floopy]

Funny,
That instrument has the tag Brigham Young university, that's where I'm going, I asked the welding shop here and they said they could try and it might work, but could not guarantee the result. I'm still debating whether I should let them try tig welding it.

Thank for the reply

I'm still looking for a solution to the crack in the frame, but the essential is working. In total it cost me 140$, I think it's a good deal for a unit like this.

Have a look at this thread for a possible solution to the cracked frame;
https://www.eevblog.com/forum/testgear/hewlett-packard-740b-dc-standard-digital-voltmeter-(and-740a)/msg1419955/#msg1419955

It's something I will be looking at doing since I have a lot of HP delivery victims here too. 

David

[Floopy]

It's something I will be looking at doing since I have a lot of HP delivery victims here too. 
David

Well hopefully your still around. I thought that what I had done was good enough. I haven't use it a lot this past few months because of other projects that were in the way and work. I wanted to see if a certain frequency I was emitting was going to show up on the analyzer, I was just going to do this for practice. The minute I saw the screen light up I knew something was wrong. The display had shrunk and there was a brighter than usual spot. For some reason the beam was overlapping! (see video)

Back on the bench, opened it up again. I knew it wasn't the problem, but I thought I would check the voltage rails. 81.3V Something is deteriorating I don't know what! I haven't checked any of the caps for leakage or correct value. I have to check the schematic again.

Anyway not the main problem, I'm guessing something is wrong inside the IF section of the analyzer. I need to look into it further. I found the manual and a block diagram. This one is going to be interesting.

On the bright side, I got the crack repaired! The welding shop asked 50$ to get it repaired, I asked if I could just pay for the supplies and time on the welder, but they didn't want to. I ended up buying some aluminum brazing rods. I had some trouble at first, heating a large piece of aluminum takes longer than you would expect. I forgot to clean more than just the crack on one side and it bulge a little. It holds well, I got some 220 grit sand paper and finished up the frame. I have some before and after pictures.

For a first time I don't think it looks too bad. I've only done copper pipping before.
Things to consider next time:
#1: hold the torch farther away from the work. It's easy to think that more flame will heat the work faster.
#2: Clean the work area thoroughly before applying the heat. I did one side, but the other did not get as much cleaning.
#3: put down the brazing rod before taking of the safety goggles. I have a nasty red spot on the side of my cheek now.

I'll study the schematic, there's a lot more components in the IF section than in the power supply. I think that some component is dying slowly in the power supply.

This is taking longer than I had anticipated, but there's a lot to learn in the process.

[Floopy]

More pictures...

[Floopy]

I noticed they are a bit blurry. Oops

[factory]

It's something I will be looking at doing since I have a lot of HP delivery victims here too. 
David

Well hopefully your still around. I thought that what I had done was good enough. I haven't use it a lot this past few months because of other projects that were in the way and work. I wanted to see if a certain frequency I was emitting was going to show up on the analyzer, I was just going to do this for practice. The minute I saw the screen light up I knew something was wrong. The display had shrunk and there was a brighter than usual spot. For some reason the beam was overlapping! (see video)

Back on the bench, opened it up again. I knew it wasn't the problem, but I thought I would check the voltage rails. 81.3V Something is deteriorating I don't know what! I haven't checked any of the caps for leakage or correct value. I have to check the schematic again.

Anyway not the main problem, I'm guessing something is wrong inside the IF section of the analyzer. I need to look into it further. I found the manual and a block diagram. This one is going to be interesting.

On the bright side, I got the crack repaired! The welding shop asked 50$ to get it repaired, I asked if I could just pay for the supplies and time on the welder, but they didn't want to. I ended up buying some aluminum brazing rods. I had some trouble at first, heating a large piece of aluminum takes longer than you would expect. I forgot to clean more than just the crack on one side and it bulge a little. It holds well, I got some 220 grit sand paper and finished up the frame. I have some before and after pictures.

For a first time I don't think it looks too bad. I've only done copper pipping before.
Things to consider next time:
#1: hold the torch farther away from the work. It's easy to think that more flame will heat the work faster.
#2: Clean the work area thoroughly before applying the heat. I did one side, but the other did not get as much cleaning.
#3: put down the brazing rod before taking of the safety goggles. I have a nasty red spot on the side of my cheek now.

I'll study the schematic, there's a lot more components in the IF section than in the power supply. I think that some component is dying slowly in the power supply.

This is taking longer than I had anticipated, but there's a lot to learn in the process.
Temporary link to video, I had to put it on my onedrive. It also plays it that way you don't have to download it.

I'm still here, it's quite easy to miss threads as there is more stuff to look at than I have spare time.

Sounds like the same area of the power supply has gone wrong again, the shrinking display on the CRT could be linked to the -100V supply failing causing lower HV.

Yes the modules look a nightmare to work on without the appropriate extenders & all the test gear in the manual.

I can't get the video to work, it just comes up with a login page.

The case repair looks good to me, I think I should have some practice on something that doesn't matter first, as I've only had a couple of hours training at work on copper pipe (for new work starting soon). I seem to remember the trainer mentioning you need to get the right brazing rods for the material and the some of the cheap ones weren't very good.

David

[Floopy]

Oops, the link timed out early. The problem is not a shrinking display, but the signal is not being drawn correctly. I took individual pictures. I believe it is the IF section because it is the one who draws on the X axis. As you can see in the picture one spot is brighter than the rest of the display. As I move the wave form to the left it "wraps around" and goes to that spot. I've never seen a problem like this one. This one won't be easy to identify. I'm also going through every component and seeing if the values match the ones written in the schematic.

I used these rods https://www.amazon.com/gp/product/B0000CBJGI/ref=oh_aui_detailpage_o02_s01?ie=UTF8&psc=1
They worked well after I learned to use them.

[kirill_ka]

Did you try manual sweep? Is it ok?

[factory]

Oops, the link timed out early. The problem is not a shrinking display, but the signal is not being drawn correctly. I took individual pictures. I believe it is the IF section because it is the one who draws on the X axis. As you can see in the picture one spot is brighter than the rest of the display. As I move the wave form to the left it "wraps around" and goes to that spot. I've never seen a problem like this one. This one won't be easy to identify. I'm also going through every component and seeing if the values match the ones written in the schematic.

I used these rods https://www.amazon.com/gp/product/B0000CBJGI/ref=oh_aui_detailpage_o02_s01?ie=UTF8&psc=1
They worked well after I learned to use them.

But the display does seem to have lost 20% of the horizontal in the same way that the -100V supply has gone down approx 20%. Can't really comment on the 8552B, as I only have the 8552A (still not tested).

Will have to find a local supplier for the rods, amazon UK don't have them at sensible price (about 10x the price over here).

David

[Floopy]

I did a thorough check of all components testing every single one of them. That included de-soldering one leg and checking for correct values. I found 4 resistors that where completely off value (28k instead of 40k!). I tested the diodes for forward voltage, but I don't know how to test the zener diodes for reverse voltages. I'm going to order a new set of capacitors just in case if changing the resistors does nothing. I'm getting tired of ordering a few parts and then finding out I need more. Where I live everything has to be bought online. Anyway, I'll be testing the bigger can capacitors.

I used this technique of trouble shooting when I don't know what the problem is. I just go through every component and put a black dot on the ones I have already tested. It's tedious, but I am able to find out what values are off. The only problem is that it only checks the components when they are not running. It doesn't mean that when power is flowing through it, it will behave the same way.

The hunt continues!

[Floopy]

I did forget to mention.

Some of the light bulbs had burnt out in the IF section. I replaced them all and the ones that where too expensive to buy where replaced with LEDs with resistors. It looks nice now with all the lights turning on.

I still can't believe that you can buy a replacement bulb on amazon for a 55 year old machine!

[factory]

I did a thorough check of all components testing every single one of them. That included de-soldering one leg and checking for correct values. I found 4 resistors that where completely off value (28k instead of 40k!). I tested the diodes for forward voltage, but I don't know how to test the zener diodes for reverse voltages. I'm going to order a new set of capacitors just in case if changing the resistors does nothing. I'm getting tired of ordering a few parts and then finding out I need more. Where I live everything has to be bought online. Anyway, I'll be testing the bigger can capacitors.

I'm curious as to where the drifted resistors are in the circuits, are they related to the problems you've had?

It's probably best to check to Zeners powered up in circuit for the correct voltage given on the diagrams (most will have a 5% tolerance, voltage reference ones may be better tolerance), they could also be tested out of circuit with an appropriate power supply & current limiting resistor (to limit to something like 5mA), but they can get easily damaged by removal (if glass) or from overcurrent. Equivalent types of Zener diodes don't always behave the same in circuit as the originals either.

I did forget to mention.

Some of the light bulbs had burnt out in the IF section. I replaced them all and the ones that where too expensive to buy where replaced with LEDs with resistors. It looks nice now with all the lights turning on.

I still can't believe that you can buy a replacement bulb on amazon for a 55 year old machine!

Which lamps were too expensive? Most are common types that will have used in lots of stuff until LED's became more commonly used.

David

[Floopy]

I'm curious as to where the drifted resistors are in the circuits, are they related to the problems you've had?

It's probably best to check to Zeners powered up in circuit for the correct voltage given on the diagrams (most will have a 5% tolerance, voltage reference ones may be better tolerance), they could also be tested out of circuit with an appropriate power supply & current limiting resistor (to limit to something like 5mA), but they can get easily damaged by removal (if glass) or from overcurrent. Equivalent types of Zener diodes don't always behave the same in circuit as the originals either.

I'll just grab my 100V bench power supply and do it! (I wish) or I could measure the voltage drop while it's running. I'll have to see

CM2107  (for CHICAGO MINIATURE / CML)  I couldn't find them cheaper then 2.99$ for one. I needed two and that doesn't include the shipping.

The other ones where 367 bulbs. I got those for .75$ a piece and free shipping.

Question: do film capacitors work just as well as electrolytic. They seem to be the only kind you can buy that have a 200VDC rating. I probably won't replace them, but I would just like to know.

I'll get a picture soon.

[Floopy]

The components with the scribble and the lifted leg are off value. Mostly burnt ones. I will replace the resistor I had swapped thinking it would fix it.

[factory]

I'm curious as to where the drifted resistors are in the circuits, are they related to the problems you've had?

It's probably best to check to Zeners powered up in circuit for the correct voltage given on the diagrams (most will have a 5% tolerance, voltage reference ones may be better tolerance), they could also be tested out of circuit with an appropriate power supply & current limiting resistor (to limit to something like 5mA), but they can get easily damaged by removal (if glass) or from overcurrent. Equivalent types of Zener diodes don't always behave the same in circuit as the originals either.

I'll just grab my 100V bench power supply and do it! (I wish) or I could measure the voltage drop while it's running. I'll have to see

CM2107  (for CHICAGO MINIATURE / CML)  I couldn't find them cheaper then 2.99$ for one. I needed two and that doesn't include the shipping.

The other ones where 367 bulbs. I got those for .75$ a piece and free shipping.

Question: do film capacitors work just as well as electrolytic. They seem to be the only kind you can buy that have a 200VDC rating. I probably won't replace them, but I would just like to know.

I'll get a picture soon.

I only mentioned other ways of testing the Zener as I collect old test gear, I have a few suitable power supplies & a decade resistance box for current limiting. But I would normally just check them in circuit with the DMM as it's quicker & easier, only if I suspect a problem might I check with something else.
I've recently just acquired another suitable power supply (HP Harrison 6209A 300V) for the collection, I think it may need a bit of work and also the current control sacrificed itself to save the rest of the unit from damage during shipping.

Another way of testing Zeners & other components is using my Heathkit curve tracer (with an X-Y scope), it has 0-40V & 0-200V supplies inside for testing.

CML (now VCC) have discontinued the 2107 10V 40mA lamp, other brands are still available if you search for #2017 bulb/lamp. Or you could have tried the 12V version (#2174 lamp) for a longer life, with a slight reduction in brightness, Mouser have them at approx .68$ each. Having said that the LED conversion will probably outlast them too.

https://www2.mouser.com/ProductDetail/JKL-Components/2174?qs=sGAEpiMZZMtj1PWpWL2%252bvDwicDUvKr1eMp%2f%252bXqB0Bog=

Are the 200V rated capacitors your asking about the orange Sprague ones on the power supply circuit board? If yes these are good quality film ones and shouldn't need replacing.
If not 200V is a non-standard voltage rating for capacitors these days and can be replaced with a higher voltage one eg. 250V.
The other three capacitors (metal cased) are Tantalum ones, again they shouldn't need replacing unless they measured bad. Or are Sprague type 109D (wet Tantalum type), usually you can see those easily as they rot badly if they leak.
Film capacitors are usually a lot bigger than electrolytic types for the same value/rating, so not usually practical to change them to film, ESR may be different too.

David

edit: Picture of some rotten Sprague 109D capacitors below for reference.

[factory]

The components with the scribble and the lifted leg are off value. Mostly burnt ones. I will replace the resistor I had swapped thinking it would fix it.

Those look like;
R431, 49.9k
R433, 100k
R454, 22.1k
R467, 30.1k

The first three are part of the adjustment resistor dividers for the +250V & +100V supplies and R467 is one I mentioned before (looked discoloured) in the -100V supply.

Make sure that any replacements are similar physical size or they may overheat too, you may need to up the wattage when looking as 1/2W (from the manual) are usually far too small these days.

David

[Floopy]

 

Make sure that any replacements are similar physical size or they may overheat too, you may need to up the wattage when looking as 1/2W (from the manual) are usually far too small these days.

Well darn, I hadn't thought about that when I order the parts on Thursday. They are all about half the size of the old ones. I'm still learning how to order the right components. Next time I'll place an order I'll make sure to buy different kinds. I'll use the ones I ordered just for testing purposes. Then I'll remove them.

What's the difference between metal film and thin film resistors?

[factory]

Make sure that any replacements are similar physical size or they may overheat too, you may need to up the wattage when looking as 1/2W (from the manual) are usually far too small these days.

Well darn, I hadn't thought about that when I order the parts on Thursday. They are all about half the size of the old ones. I'm still learning how to order the right components. Next time I'll place an order I'll make sure to buy different kinds. I'll use the ones I ordered just for testing purposes. Then I'll remove them.

What's the difference between metal film and thin film resistors?

It seems very little for the ones you have ordered, the metal film usually have a round cross-section same as the old ones and the thin film types are usually flat on a piece of ceramic  (but the data-sheet for the MBB type ordered says they are round metal film too). 

Here is the data-sheet for the SFR metal film resistors from your order,
https://www.vishay.com/docs/28722/sfr16s25.pdf
And the MBB metal (thin) film type,
https://www.vishay.com/docs/28768/mb_vg06.pdf

If you keep them spaced off the board when testing it should prevent any board damage if they overheat.
You may need to look for 1W or 2W to find similar size to the originals. Not sure why they specified 1% if they wanted values like 22.1K as it could be anywhere between 21.879 & 22.321, this should allow you to round the numbers off it you can't find the exact values at the higher wattage.

David

[Floopy]

I finally found all the parts I needed. I tried getting them all from the same manufacturer, but in the end I had to diversify in between Xicon and Vishay. Unfortunately one item is back ordered. The shipment is suppose to come around Sept 12. For now I'll just put everything aside and hope that the parts can come quick, because I'm getting tired of waiting for parts.

[Floopy]

Got the parts earlier than expected. The resistors are almost the same size as the old ones, but after hours of searching for the same brand with the right values I think I did what I could. After some soldering I turned it on. After some measuring and some tweaking every line came to their correct voltages. Even after waiting half an hour it was all staying within a .04% tolerance. Modules plug-in and all!

Lets hope it stays that way...

The display reverted back to normal. Maybe it was due to a bad voltage rail, only time will tell. I left it running for some time and after a while I turned it off and touched the resistors. They seem warm, but not burning. I will have to measure the temperature.

I thought that I had taken a picture of the board after, but apparently I didn't. The new resistors are about 3/4 the size of the old ones. I also found that the analyzer works well with my pen plotter. The pen lift output will create a "break" in the paper. I guess I can call that the "save" feature. I'll take a picture of the final unit. I didn't replace the capacitors after all. Now I just need to find a VHF or UHF frequency generator to calibrate it.
(I remembered that I had a 275V power supply and it had a limited current output at just 50 milliamps. )

[factory]

Good to hear it's sorted  , it's surprising the difference just one incorrect supply rail can cause, I thought I had all good power rails in a counter I'm repairing but completely missed the separate one for the oscillator (down 25% causing the main 5Mhz output to be too low to operate rest of the counter circuits).

Your 275V 50mA power supply is more than enough to check Zener's if you wanted to, you would need to calculate the series resistor to prevent destroying them. The output capacitance is usually enough to short Zener's if you don't (been there done that at work, luckily it didn't matter as we had plenty of new ones).

David

[Floopy]

I did all the calibration procedures this week on the RF section. I didn't do the ones on the IF section because I don't have a UHF generator. I will have to find one somewhere. For now it works well and I can see my local radio stations popping up on the screen.

Hopefully I can say that I'm done for now.

[Floopy]

It's me again!
At this point I might just be talking to myself though. I don't know someone might find this useful. At least I've learned a lot.

I've been quite happy with this boat anchor so far. I've only had to replace the fan because the unit was over heating and the thermal shutoff would turn on. Now it handles much better, but it is a bit noisier. I wish I could thank the engineers for putting easily available parts.

I've got a new problem and this time it's with the display again. I noticed that it's shrunk. It's a bit smaller on the edges and when I try to adjust the horizontal gain it maxes out. I'm dig deeper into the service manual and see. In the mean time anyone have an idea of their head what it might be? I also noticed that the "scanning" light never comes on except a few times on power up then it turns off. Also when I start getting near 0-10Mhz the signal seems to be mirrored around some axis. Could all of these seem to be related.

The display is showing a 833Mhz -30db signal.