HP 54501A Restoration and Calibration

[xrunner]

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

Wonder if they'll honour that? 

Gee I dunno. Hey I know - I'll drop the confirmation card in the mail (see attachment) and see if it gets returned. Maybe there's a crew of engineers there that were never notified of the company change. If it doesn't come back, we only have a PO box to go on ... somebody needs to find out whose getting their mail. 

[xrunner]

Next up is making two replacement cables for the DC & AC calibrator connections. Only one is damaged but just so they look the same I'm going to make two new ones. Have the SMB parts and RG-174, waiting on the BNC parts.

[TAMHAN]

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

Wonder if they'll honour that? 

My memory is fading a bit now. But I can remember that Intel still honors the guarantee for the Pentium I according to the German c't newspaper...

[xrunner]

My memory is fading a bit now. But I can remember that Intel still honors the guarantee for the Pentium I according to the German c't newspaper...

Maybe I should try to send the cope back LOL. The safety notice states that if the ground connection doesn't pass the test to send it back. OK it's 26 years later, but since it's a safety issue and the part isn't available now, maybe they will send me a brand new Keysight scope! 

[xrunner]

Got the brand new Schaffner line filter today. There was still one thing about it I couldn't tell from any pictures. The new switch block that it comes with - as labelled - is wrong for the 120V position. The 220V position, is the correct one for the old way the PSU was wired, back in the day. 

So, I can easily make it work, but I will use the old switch block in the new filter. Welcome to restoring old equipment.

Also got the BNC connectors I need - so I should have all the parts now.

[tautech]

Got the brand new Schaffner line filter today. There was still one thing about it I couldn't tell from any pictures. The new switch block that it comes with - as labelled - is wrong for the 120V position. The 220V position, is the correct one for the old way the PSU was wired, back in the day. 

So, I can easily make it work, but I will use the old switch block in the new filter. Welcome to restoring old equipment.

Also got the BNC connectors I need - so I should have all the parts now.

Quadruple check that, sketch it out and be sure.
Is there no way the wiring can be reconfigured to make the switching correct?

[xrunner]

Quadruple check that, sketch it out and be sure.

I did, I octuple (is that a word) checked it, I just tested it with the scope and it works OK.  If that thing had blown my project I'd never have been able to face the forum again. 

Is there no way the wiring can be reconfigured to make the switching correct?

Nope. Not in any practical sense of the word. The problem lies inside the new design of the Schaffner filter. Something, for some reason, caused them to change the design back in 1993. For some reason an industry standard changed and they don't make these parts with wiring like the old ones. It's not possible to open it and change the wiring because it's all buried in potting compound. I wish there were a way. I've stared at that schematic for hours and there is just no way to undo what is done inside the thing with extra wiring outside. There is no way to undo a "short" with more wiring, something like that concept.

But, all is well. I will now drip some epoxy into two of the ports back inside where the switch block fits, to prevent it from inserted upside down, and call it done.

[xrunner]

Is there no way the wiring can be reconfigured to make the switching correct?

Well, it's going to be OK, and work as originally manufactured. Not being one to give up easily and look things over again, I took another look at exactly what these diagrams meant in terms of what's inside the filter and what the switch block does. It's a little confusing, because the diagram doesn't clearly show what part of the circuit is the switch block and what isn't. What changes are hardwired and what aren't.

Also, I had in my mind what the Schaffner engineer told me over the phone, that it would work on 120 but not 220 as compared to the old model. But, it turns out, if you use the old switch block in the new filter, it will make the changes that are required the same way as the old model. That's one thing the Schaffner guy didn't take into account, and probably wouldn't have realized, is that I have an old one with a different switch block that I could use in the new one.

Anyway - gah - I won't have to make any label changes to tell people now. It sometimes takes me a while, but I get to the end of the yellow brick road.

[xrunner]

Made up the new replacement cables that connect the DC and AC calibrator outputs to the rear panel. Installed new Schaffner filter. Back panel finished - good as new.

[xrunner]

It's done! 

Works well, for me it's a nice unit for my collection too.

Got my eye on another used piece of test equipment, may have another thread coming ... 

[tautech]

Nice.
Looks really sharp, thanks for sharing. 

[AF6LJ]

It's done! 

Works well, for me it's a nice unit for my collection too.

Got my eye on another used piece of test equipment, may have another thread coming ... 

This was a great thread, your scope came out really nice.
I am looking forward to your next installment.

[xrunner]

Thanks to you and everyone that made suggestions. That Schaffner filter was a pain! 

[rf-loop]

Nice work!

Also nice to see peoples want restore these old well designed and made beauties.

I hope also thät today chinese designers looks and learn how carefully these equipments user interfaces are designed.
There is difficult to find any bug or design error. UI ergonomy, useability is really designed by peoples who really know how equipments are used in real work.  (Of course it is old and performance is technically obsolete but this is other thing)

[xrunner]

Nice work!

Also nice to see peoples want restore these old well designed and made beauties.

Thank you.

I enjoy doing it, and I hope the threads I post (and others that are doing outstanding restorations) will be available for years to come, so that others wanting to do the same thing for these great vintage instruments will be helped in some manner. Things in the future will never be made the same way, and it's important to preserve the quality of some of these instruments.

And many thanks to the EEVBlog for hosting these threads!

[roberto]

Hi, gentlemen and thank for the support.

I bought one used HP 54501A and I LOVE IT but.

It gave me problems when I use it for a while, I had a bad smell (non electronic blowing components) and the oscilloscope cause differential relay action.

In my opinion is the power supply or something similar, do you think can be the Schaffner filter?

I'll change it immediately.

Tanks for support, cheers RA

[Tim88]

BTW, I'd strongly recommend to replace the Schaffner mains filter if that hasn't been done in the last 10 years as they tend to blow up and spread some corrosive gunk all over the mainboard. They are still made, usually not very expensive, and the new versions should be more reliable. Just make sure you don't buy "new - old stock" as that wouldn't really solve your problem.

Yea thanks - I've heard about that and I'm going to attempt to find a replacement that fits in the existing cut-out.

Here's a few more screen shots for today. I'm just posting these for anyone browsing the web looking for info that may need to see them.

So, I know that the NVRAM is bad (really the battery inside), so what happens when you run the self-test? On the back of the unit is a red switch that sets the calibration to either protected or unprotected. If that switch is in the unprotected mode, you see that it passes all the self tests (with a bad NVRAM). If it is in the protected setting, the self-tests do not pass the NVRAM, D/A converter, or A/D converter (with a bad NVRAM). And finally, you can see the screen at the completion of the self-calibration. However, once you turn it off it will all be lost with a bad NVRAM; but it does complete properly. 

Only other thing I've done is to pull out the power supply to see if it can be jury-rigged in such a manner as to allow one to tweak the tweakable adjustments underneath it without using the "extender cable" the manual talks about - I think it will be possible.

More to follow ... 

Man, sure am glad I stumbled across this post. I picked up a 54502A a while back that didn't want to power up. When probing for voltages, something sparked and it powered up. Was planning on eventually replacing it not knowing the darn thing can explode black gunk all over the place. Thanks!

[xrunner]

Man, sure am glad I stumbled across this post. I picked up a 54502A a while back that didn't want to power up. When probing for voltages, something sparked and it powered up. Was planning on eventually replacing it not knowing the darn thing can explode black gunk all over the place. Thanks!

Glad you found it. If you have any pics of your work post them here.

[midtex]

Hello there. New member here. I recently bought an HP 54501A for cheap, knowing that the NVRAM issue was what was causing the self-test failures. I replaced the Dallas chip with genuine item from Mouser. The unit passes all self tests and I have gone through several of the training exercises detailed in the Quick Start guide. Everything works exactly as it should - except......

The vertical axis seems to have a small amount of ripple in the signal. All voltages whether sine or square or DC all "wiggle" for lack of a better word. If I tell the scope to display real time voltage, the number is not steady, but jumping all around by several tenths. The background video - scales, menus, labels, etc are all rock steady, so this is not a CRT issue. It is only measured signals and it does this whether using the rear DC or AC reference ports, or when using an external signal generated by a function generator.

I was wondering if anyone has any suggestions of where to start? I'm guessing it is possibly a reference voltage that is not regulated properly? Would this likely be a power supply issue or main board? I do not have a schematic, but do have the service manual which does provide information on some calibration.

Thanks in advance for any advice!

[Tim88]

Mine had a bad power entry module that was bad, it is a common failure I believe. Its the module that the line cord plugs into. They don't make them any more but there is a replacement available. I am not at home so don't have my notes handy but there is info on it on the interweb.

[cjuried]

Hello all,

I have one of these units that passes all selftests except for a failed AD Converter. Any thoughts on suspects I should keep my eye out for? HAs this been a common issue with these units?

Thank you,

Chris