HP 54501A Restoration and Calibration

[xrunner]

The NVRAM is now installed and I went through the self-cal and logic trigger delay cal to make sure it would save the results. All passed. It now comes up with no error messages and the waveforms are displayed properly with respect to their amplitude and offsets, and the triggering works correctly.

Yippee! 

Next up is the manual adjustments on the main board, after which I'll do another self-cal

[xrunner]

Proceeding with the manual system board calibration. Section 4-14 Track and Hold Offset.

This is what the signals at TP1 and TP2 look like when the adjustments are complete using R274 and R74.

Refer to Service Manual pg. 4-9

[xrunner]

I found an archive picture on the internet of the lab console and equipment where I worked - the AFEWES lab (Air Force Electronic Warfare Evaluation Simulator). There is an HP 54501A there in situ.

Can you see the 54501A in the rack?

[xrunner]

Several of the adjustments cannot be accessed without the extender cable set because the PSU is in the way, specifically, some trimmer caps near the front of the scope. I was able to adjust many of the pots toward the back with the PSU in-place (because my hand is small), but the ones up front just cannot be done.

I'm going to re-arrange the PSU so that the scope will still operate and so that I can get to the caps. I found that it can be operated when connected in the geometry shown in the picture

It looks a little scary but I'll be OK. 

[AF6LJ]

Whatever you do BE SAFE

[xrunner]

Whatever you do BE SAFE

Thanks Sue - no problem. It looks hokey but it's very safe. 

[AF6LJ]

Whatever you do BE SAFE

Thanks Sue - no problem. It looks hokey but it's very safe. 

Doesn't look that bad to me, I have done similar.

[xrunner]

Well I'm still alive. 

I had to move the PSU as shown (because I did not have the "extender cable" for this scope) to complete the Attenuator Compensation Adjustments - Section 4-15. It states to use a 100 Hz square wave, 300 mV pp, into a 50 ohm termination at the scope. However, using the given parameters of the square wave they stated, I found that adjusting the compensation caps produced absolutely Zero observable change in the response to the square wave on any of the four channels. I decided to change the freq. of the square wave to 10 kHz and that allowed me to see and make the adjustments. Don't know if the manual has a mistake, but it seems so.

So having completed that part of the cal, I put the PSU back the way it's supposed to be.

[rf-loop]

Well I'm still alive. 

I had to move the PSU as shown (because I did not have the "extender cable" for this scope) to complete the Attenuator Compensation Adjustments - Section 4-15. It states to use a 100 Hz square wave, 300 mV pp, into a 50 ohm termination at the scope. However, using the given parameters of the square wave they stated, I found that adjusting the compensation caps produced absolutely Zero observable change in the response to the square wave on any of the four channels. I decided to change the freq. of the square wave to 10 kHz and that allowed me to see and make the adjustments. Don't know if the manual has a mistake, but it seems so.

So having completed that part of the cal, I put the PSU back the way it's supposed to be.

And what is your square wave rise time and other signal charateristics. Adjustments need do with equipments what are listed in service manual or comparable. In this case HP8116A programmable pulse fenerator. If not available, then need look carefully HP8116A specifications and use something what is as near as possible (because in service manual, text is valid for named equipments)  There is quaranteed rise time and overshoot etc.
Every step in HP service manual is just perfectly right.  This is not made in china.

Also it is good practice to follow paragraph 4 order starting from 1, every step in order. This is how it is designed to do. (if know exatly what is doing then also know where can do different and how to execute own procedure)

 If on your board things do not go as in manual, there is two reasons, device is somehow failed or you do something wrong. One problem where things do not go as in manual may be wrong instruments used for job.

[xrunner]

And what is your square wave rise time and other signal charateristics. Adjustments need do with equipments what are listed in service manual or comparable. In this case HP8116A programmable pulse fenerator. If not available, then need look carefully HP8116A specifications and use something what is as near as possible (because in service manual, text is valid for named equipments)  There is quaranteed rise time and overshoot etc.
Every step in HP service manual is just perfectly right.  This is not made in china.

Uh - yea, I know it's not made in China, it's made in the U.S.A. 

I do not have the specified pulse generator, so I'm using the best I have - a Rigol DG1022 which has the following specifications for the square wave -

Rise/Fall Time < 20 ns (10% to 90%), (Typical, 1kHz, 1 VPP)
Overshoot < 7.5% (Typical, 1kHz 1Vpp)

It may not be fast enough rise time, but I'm not going to go out and buy a specific pulse generator just for one alignment on one scope. I'm dong a restoration the best can do with what I've got at the moment.

Besides, I was able to do a decent job by just using a higher frequency square wave which clearly showed me the adjustment changes. If the adjustment for the 100 Hz square wave (using the generator specified in the manual) were to have been in a different position than it is now (meaning the position I adjusted it to for the 10 kHz F), then the higher frequency square wave would have looked terrible. So you see, the adjustment now has to be very, very close to what it should be anyway, or the higher frequency would not look flat. There is not a different adjustment compensation capacitor for different frequencies - only one. It can only be in one position when you are done. Do you understand that?

Also it is good practice to follow paragraph 4 order starting from 1, every step in order. This is how it is designed to do. (if know exatly what is doing then also know where can do different and how to execute own procedure)

Yea, yea, I did follow it in order ... Give me a little credit LOL.

If on your board things do not go as in manual, there is two reasons, device is somehow failed or you do something wrong. One problem where things do not go as in manual may be wrong instruments used for job.

Manuals have errors from time to time, I'm not talking about HP specifically now but in general. But I want you to look at an attachment I scanned in from the manual for my HP 5334B, and read the text right under ABOUT THIS SUPPLEMENT and tell me what it says there ... remember this is an HP manual. 

I've seen errors in manuals before. So to claim it doesn't happen is just factually incorrect. Things can go wrong because of three reasons - device is somehow failed, you do something wrong, or there is an error in the manual procedure.

And as I said, I'm not going to buy the exact generator or a new generator that has the exact characteristics of the one specified in the service manual just for this one specific alignment (if that's what the problem is). If I get a better one (waveform generator) someday I'll go back and see if what you say is true, but for now it's as good as it's going to get, which is pretty damn good.

There are several things I need to do now. I need to finish the alignment checks, the only one left is the Oscillator Output Check. Then I will be making two new cable assemblies for the Ac and DC calibrator outputs on the back. Even though only one is bad, I'm just going to make two new ones so they match.

[rf-loop]

I know.  I have lot of HP/Agilent Tektronix manuals etc errata and correction sheets. Some of them also very severe.

Also I know how to repair calibrate and adjust HP545xx scopes. I have done these more than "lot". Just boring work for salary. In some storage I think I have still couple of these (severe failed) for recycling.

Usually (mostly) these models do not need readjust exept if example mobo is changed. Mostly they pass specs for cal without adjustment. Main principle for adjustment is that first need be sure that something need really adjust. But, this particular case is so easy that it can do also nearly how ever. But if do not think just this case, I have seen it so many times over years that with wrong equipments someones have made "adjustments" and things have gone only more bad than before adjustment. (I do not mean you do it so)  This scope is easy piece of  bisquit because it is only 100MHz BW and there is only very extremely limited things what can adjust at all.

[xrunner]

Usually (mostly) these models do not need readjust exept if example mobo is changed. Mostly they pass specs for cal without adjustment. Main principle for adjustment is that first need be sure that something need really adjust.

Yea but I like to adjust things - even if they may not need it. 

I paid for this ticket and I want the whole roller coaster ride. This is my entertainment don't you see? 

[Wuerstchenhund]

I also want to hear from Wuerstchenund because he said they were still available. I sent him a PM and I'd like to know if he knows of any new old stock somewhere becasue that original part is not available as new.

Sorry for only replying now but I was down with a cold.

When I said that replacement for that Schaffner mains filter is available I did not mean the original part, which is no longer made (the whole line has been redesigned, also because of the tendency to explode). But Schaffner has other models that fit the cutout and allow 120V/240V switchover. I can't remember what the exact model was I used in my 54510A but I remember that I had to modify the mains voltage switching logic for the new module slightly. I decided against hard-wiring the mains voltage to 240V, which would have created some potential issues for people that owned the scope after me.

In any case, Schaffner should be able to tell you what the suitable replacement models are.

Keep in mind - I know of nothing wrong with the part that's in the unit right now. I was just advised that they blow out by Wuerstchenund. Maybe it's not a big deal, how many blow out, what percent blow out? Any given part can fail. I mean the thing's been around for 27 years and the part is still working just fine and I can get the actual part (used) on Ebay right now ... 

The question is not *if* your old filter will explode, the only question is *when*. All these old Schaffner filters will blow up eventually, as due to their age the caps in them become dry, heat up, and due some design issue this is pretty much guranteed to end up in a more or less violent disintegration. There are no external signs telling you if your filter is going to explode tomorrow or in a year, and no warnings before it happens. The fact that your scope's filter is still working is probably down to being operated at 120V mains, as the speed of aging is also dependent on the mains voltage (so filter operated at 240V will age faster to some extend). But that doesn't mean that your filter is fine, it has passed its best-by date a very long time ago, like every single filter of that series that was made.

There's absolutely no point in doing any restorative work on the scope while leaving the original filter in place. When it pops it will blow a large load of dark, corrosive gunk on your nicely restored scope, which in the best case is just a hell of a pain to clean up and in the worst case will damage your scope's PCB beyond repair.

This should also explain why looking for "new old stock" would be a silly thing to do, because no matter if used or not, this "new old stock" will have degraded as has every other filter of that series, and you're essentially just replace one time bomb for another.

[rf-loop]

Usually (mostly) these models do not need readjust exept if example mobo is changed. Mostly they pass specs for cal without adjustment. Main principle for adjustment is that first need be sure that something need really adjust.

Yea but I like to adjust things - even if they may not need it. 

I paid for this ticket and I want the whole roller coaster ride. This is my entertainment don't you see? 

Oh, in this case all can understand and yes it may be fun but also useful. Same here when I do things in hobby side... curious and experimental. Still one Collins Receiver is waiting if I like start adjust it - there is totally out of order this bit complex mechanical variable IF tuning system.

[xrunner]

Sorry for only replying now but I was down with a cold.

No problem.

When I said that replacement for that Schaffner mains filter is available I did not mean the original part, which is no longer made (the whole line has been redesigned, also because of the tendency to explode). But Schaffner has other models that fit the cutout and allow 120V/240V switchover. I can't remember what the exact model was I used in my 54510A but I remember that I had to modify the mains voltage switching logic for the new module slightly. I decided against hard-wiring the mains voltage to 240V, which would have created some potential issues for people that owned the scope after me.

In any case, Schaffner should be able to tell you what the suitable replacement models are.

Yes, as I learned (I called Schaffner USA), and I'll attach the revision again for you if you're interested, the new model which fits the cutout exactly and has the same connector, was re-designed. It switches internally differently for 220V than the old model. I have no idea why this change had to be made. But - the new design (-11 see attachment) is no different in the 120V switch block position, which means I could install it and use it just fine here.

So, what I'd like to do is buy a brand new model - the FN 393-2.5-05-11, and mark out or black out the lettering on the reversible switch block so there is no 220v option indicated to the user, and also label the rear so as to indicate it is only for 120V. As you can see from the second attachment, even if I put in a different model filter and re-wired the internal wiring, there is still lettering on the back that indicates 120V/230V in two places. I mean, unless I scrape that off also, I can't prevent a person from doing something dumb and connecting it to 220V, if it ever left the US. So do you think it's acceptable to replace with the new design and black out the lettering on the reversible block so that 220V is not indicated? Is that acceptable?

The question is not *if* your old filter will explode, the only question is *when*. All these old Schaffner filters will blow up eventually, as due to their age the caps in them become dry, heat up, and due some design issue this is pretty much guranteed to end up in a more or less violent disintegration ...

Yes I agree with all of that statement ^^^

[Wuerstchenhund]

So, what I'd like to do is buy a brand new model - the FN 393-2.5-05-11,

Probably no bad idea. I think that's the model I bought when I replaced the one in my old 54510A.

and mark out or black out the lettering on the reversible switch block so there is no 220v option indicated to the user, and also label the rear so as to indicate it is only for 120V. As you can see from the second attachment, even if I put in a different model filter and re-wired the internal wiring, there is still lettering on the back that indicates 120V/230V in two places. I mean, unless I scrape that off also, I can't prevent a person from doing something dumb and connecting it to 220V, if it ever left the US. So do you think it's acceptable to replace with the new design and black out the lettering on the reversible block so that 220V is not indicated? Is that acceptable?

Frankly, I'd do it properly and keep the device 120V/240V switchable. Aside from that disabling the voltage switching is more of a hack job (in which case it would be easier and look more professional to just buy a FN390 Series filter without the voltage switch instead of black-felting a switchable filter), disabling the voltage switch facility could well have other implications. Fact is that the 54500A Series has been specc'd by the mfg for 240V compatibility, and it's not unreasonable for people to rely on that spec. So if you disable the 240V mode, and someone buys your scope (i.e. as a replacement for an existing ATE), powers it up at a 240V mains line and the PSU blows up (potentially causing further damage beyond the scope), you might well end up being liable, and I wouldn't count on that simply blackening/scraping out 230V markings would cover your ass. Chances of this happening are probably slim but it's enough if that ever happens once with the scope you sold, which has some potential to ruin your day.

My recommendation is to do the work properly. Especially since we're talking about mains voltages here, which aren't exactly insignificant.

[xrunner]

Frankly, I'd do it properly and keep the device 120V/240V switchable. ...
My recommendation is to do the work properly. Especially since we're talking about mains voltages here, which aren't exactly insignificant.

I really appreciate your help Wuerstchenhund - but how? Did you look at the change notice from Schaffner? I'm going to post the relevant schematics one above the other in this post.

They changed the way the wiring is switched inside the thing, and you know you cannot get into it to modify it. Look at the schematic. In the old one (the bottom one) and the new one (top) the 120V wiring is essentially the same as each other - the hot 120V goes into the PSU, out and right back in again, and then out back to the neutral.

They changed the way the 220V is switched though. In the old one, that "middle" loop path is simply opened and the 220V is simply across the two input terminals to the PSU. In the new way, it ain't like that. You can see the difference in the top schematic.

I do not see any way to change what they did internally on the outside of the filter. If you say buy a new filter, so it won't blow out my nice restoration, then I agree and it will live happily ever after at 120V. But you also say it's best to make it still work at 220V. How? If the person that gets it from me changes the little block so they think it's going to work at 220V, then how is it possible to keep that functionality? Like I said, what they did cannot be accessed - it's buried inside a potted case. And I see no way to reverse that on the outside to keep the same 220V option with this PSU. There is no way to "unconnect" what the switch block connects inside the filter. There is no wiring change you can make outside to reverse what happens inside when the block is set to 220V.

Does anyone else see the problem here? 

I have another idea but I want to first exhaust this issue.

[Messtechniker]

What about a big red honkin' label saying "For 120 V mains only!"
as a last resort on the unit itself on two or three places to get
you out of any liability.

Yours - Messtechniker.

[xrunner]

What about a big red honkin' label saying "For 120 V mains only!"
as a last resort on the unit itself on two or three places to get
you out of any liability.

Well, I can't have my cake and eat it too right?

It's an old piece of kit and the original part is not available brand new - they are all used old stock. It's impossible in any practical sense to buy a new one and cut it open to change the way it works. So I have two choices -

• Keep the original part that allows it to work on 220v but risk blowing black snot all over it
• Buy the brand new better part which switches the wiring differently for 220V but works on 120V.

But here's what I would like to do, to both be safe and allow the new part to be used. Keep in mind the thing would have to be sold by someone someday to a country that used 220V (I won't be the one that does that though). What I propose is to buy the new part. I will then epoxy the two top middle insertion slots in the back of the opening where the switch block goes in to prevent it from being inserted for 220V operation. As you see in the pic, the two middle prongs are what do the wiring change between 120V and 220V. They are only one one side of the block. The block is flipped over to change the wiring.

So if someone even tried to change the block, it won't go into the slot when it's turned over. It can only be inserted one way after I'm done. In the manual it states -

"Before connecting the instrument to an ac power source, ensure that the line selector module is installed for the correct voltage"

So with my epoxy mod, this will be impossible. They will have to re-install an original used part to do that, and thus the whole problem will start over for them, but at that point it's their decision to risk the filter blowing out. Really, isn't what I'm doing the safer approach? I mean, if it's common knowledge that the filter blows up, what I'm doing is the safer choice anyway.

I will also label the back nicely so that it states it's for 120V only, covering up the existing labeling on the back, and completely remove the lettering for the 220V selection on the switch block.

What else can I do given only two options?

I sure wish I knew why the stupid part was re-designed. It must have been to comply with some sort of new industry requirement.


Please find attached the pic of the switch block that is used to change the mains voltage input.

[Nuno_pt]

xrunner, it sounds like an save approach.

[tautech]

What else can I do given only two options?

Keep a mod book for the unit that stays with it and add a sticker inside and outside explaining such.
Original and modded schematic too, then only an idiot will FUBAR it.

[xrunner]

Keep a mod book for the unit that stays with it and add a sticker inside and outside explaining such.
Original and modded schematic too, then only an idiot will FUBAR it.

I'm working on that today. I have the new Schaffner filter on order.

After I get done, only a complete fool, who would not have paid attention to the original instructions and notices anyway, will be able to damage it. A fool such as I'm talking about, would simply plug a new original scope like this straight into 220V when it was set for 120V, paying no attention to the warnings on the back.

Nothing can be totally idiot-proofed. Not even HP was able to achieve such a goal. 

[tautech]

Another thought xrunner.....I've come across manuals that in the first page or so there's been a card overlay stuck in place containing country specific information, often it's the first thing you see when opening the manual.

[xrunner]

Another thought xrunner.....I've come across manuals that in the first page or so there's been a card overlay stuck in place containing country specific information, often it's the first thing you see when opening the manual.

Another thing I can incorporate is an actual warning notice from HP regarding the filter, which came with this scope in the pouch that attaches to the top of the case. You can read the attachment; I will add to the documentation, to be on the safe side, that

• The filter was changed to the modern version to avoid any problems with the issue in the notice
• The filter was changed to avoid a known defect in the original filters that cause them to catastrophically fail

However, the modern part does not allow this model scope to work with 220V, so that option has been disabled.

Yay.

Boy, this project has been interesting so far.

[tautech]

 

3rd sentence 3rd paragraph.....HP will replace the mains filter free of charge.

Wonder if they'll honour that?