HP 54501A repair — NVRAM, PSU caps, etc.

[voxadam]

I recently adopted a four channel 100 MHz 54501A.



I don't have any pictures of its guts yet but this thing is incredibly for being just shy of 28 years old (assuming that the date stamped on the inside of the case back that reads "OCT 21 1989" is indeed the manufacturing date). Judging by the calibration sticker dated 8/29/2003 it came from a DaimlerChrysler facility in Huntsville Alabama. I've only taken a cursory look inside the unit, just enough to feel comfortable enough to briefly power it up.

As expected the DS1235Y NVRAM battery is dead so that's the first order of business. I can replace the old Dallas part with, a new DS1235(Y) or, according to Wuerstchenhund[1], a Cypress STK16C88 nvSRAM[2]. I've also heard that there's an FRAM part that can be used (maybe the FM16W08) but there's conflicting information[3] on its suitability. The DS1235(Y) and STK16C88 parts are similar in price on eBay (new old stock), US$15 or less from US sellers.

From my reading the other things that I should look into replacing are the PSU caps and the Schaffner mains filter. I'm just having a difficult time deciding how far to go with this. While a HP 54500 scope is perfectly usable I plan to replace it with something a bit more modern that doesn't tip the scales at 10 kg (22 lbs) like a DS1054Z when I can.

So, while it's a bit old it's not a total boat anchor and since I spent exactly zero dollars for the scope and three 100 MHz HP probes I'd say it was a decent deal.


[1] https://www.eevblog.com/forum/repair/hp-54501a-troubleshooting-repair/msg213749/#msg213749
[2] www.cypress.com/file/111946
[3] https://www.eevblog.com/forum/testgear/hp-54501a-restoration-and-calibration/msg939719/#msg939719

[RLac]

Hello, I bought same oscilloscope (for very cheap) but I experience some troubles that I don't know how to approach (I'm a newbie).

Sorry for taking advantage of your thread to discuss about it but I thoght that's unecessary to open a new one.

In addition to RAM/A-D/D-A errors that tipically occurs when dallas nvram has the battery exausted , I had also a ' System Rom Failure '

I replaced the dallas chip with a new one from Mouser , I tried to calibrate the scope and now I have a permanent error that remains also if I clear the cycle as the advertise suggests.

I thought that maybe eproms need to be reflashed but I don't know where to find the firmware.

Thank you in advantage.

[AF6LJ]

This is going to be a good thread. 

[tinkertokyo]

I recently replaced the NVRAM on my 54501A and made a video about it. If you’re interested you can watch it here: https://youtu.be/6utAVVM58Ig

[paerley]

Intentionally Necroposting!!!

I found this thread when researching fixing the NVRam in this scope a few times.

I used a FRAM part: FM1808-70-PG after having bought a 'new' NVRAM chip (was a 'working pull', I found out later) that didn't restore it.  Because I was able to get 2 of the FRAM parts for $10 from eBay, I decided to try it and have confirmed that it works.

[rdsi]

Yep I bought my 54503A new back-in-day & still have it.
Replaced the NVRAM but have not had any problems with capacitors.
I also had to rebuild the electro-mechanical attenuator’s.
Even though they were gold plated there is still some tarnished that built-up over time.
Otherwise, this has been a great scope & still use it for HF stuff (500 MHz BW).

Here are 2 great links about the NVRAM & attenuators:

https://www.eevblog.com/forum/repair/hp-54503a-scope-attenuators/
https://www.eevblog.com/forum/reviews/hp-54502a-nearly-vintage-digitizing-scope/