HP 54501A troubleshooting - repair

[chihaxinh]

Hi rf-loop

How to use SRAM to replace NVRAM Dallas , can you guide me , i have another osc using NVRAM Dallas !

Many thank !

[Greg981]

One more update (for posterity).  I have now determined the checksums of the four original EPROMS, and compared with the replacements that I got.  One very small difference found indicates that one EPROM had indeed started to lose its contents.  Original c/sums: 80005: ED60, 80006: 48E4, 80007: CB62, 80008: 220E.  Replacement (working) set: 80005: ED60, 80006: 48E3, 80007: CB62, 80008: 220E.  Sadly I can't get my programmer to talk to my PC (perhaps something to do with using a USB/RS232 converter) so I can't view the .HEX files to compare them.

[xrunner]

I have a HP 54501A coming from Ebay. I was wondering about doing the full cal setup procedure. The service manual states you need to remove the PSU and reconnect it via an extender cable assembly, because some of the adjustments are under the PSU. Can this be done at all without the extender cable assembly?

[Smith]

I don't think so, the cable between the PSU and the mainboard is quite short. As I remember correctly you can adjust the PSU itself without an extension.

[xrunner]

I don't think so, the cable between the PSU and the mainboard is quite short. As I remember correctly you can adjust the PSU itself without an extension.

Yea I saw how you can adjust the PSU OK. I've read quite a few threads on repairing and calibrating this unit, and not one ever mentioned the extender cable. I'm not sure if everyone out there has one of those cables in their junk box (LOL), or if they are somehow doing it by manipulating the PSU. I can almost see how it could be turned 90 deg. in-place and supporting it using some cardboard or other insulating stuff.

I guess I'll find out in a week or so. 

[Smith]

I just used the automatic calibration on my 54502A, and everything works fine. Yes I double checked with external gear. There was no need to make adjustments on the main board. As I remember I never heared of anyone needed to make adjustments there.

An extender should be quite easy to make with some single male and female connectors and some not to thin wire. You don't really need the multipole male and female connector, unless you are planning to calibrate it verry often.

[bsalai]

Hi all,
I just got a 54502a. It was working fine when I picked it up, but as soon as I got it home, it developed a strange problem. As soon as I turn it in, something clicks (sounds like a small relay) and it shuts down just momentarily. Then it cycles again, sometimes rapidly, sometimes slowly. Occasionally I see a trace just for a second, but usually nothing.
I opened up the power supply, and it is very clean, no sign of trouble. I tried disconnecting the CRT board, but the trouble persists. It is difficult to pinpoint where the sound is coming from. My best guess is the front left corner of the main board, looking at the scope from the front. I haven't pulled the main board yet, but that's next.
Any thoughts??
Brad

[dpm46]

Hi to all,
      I got a hp 54522a scope. Before I got problem with power supply and already repair it.  After the scope not being used for several months a new problem now develops.  Now have d/a, a/d and much more problem.  I turn the scope overnight hoping that the problem will go away. But when i go back in the morning I heard clicking on the scope and the display is on and off. I turned it off then turned on then there is a message like this: "SOFTWARE ERROR - Please record these numbers 0034 00003588 2000"  I open the scope and found out that the capacitor that I replaced before, failed again. I replaced again but same message.. Hope you can help me...

Regards,
Dave

[tinkertokyo]

Just in case it's of any interest to someone, I posted a video of me replacing the NVRAM on my 54501A.

[yovenim]

hi guys!

i've bought 2 HP 54501A. old very-high-end scopes. 100Mhz but only 10Msa/s
one don't power on... and the other one says various error...

i'm going to post here about this repair.

scope that work bad:
various error, including a/d, memory and DAC error. smell like corrupted calibration data.
it's fault of the NVRAM (non volatile ram)... it has 2 litium battery... but not user or service serviceable...
so, i've found a compatible replacement DS1230Y-120+ from maxim. i've ordered 2 (maybe non-original) from china to be sure, but i'm going to use original and expensive ones from dallas semiconductor.
i've already removed the chip HP PC Troubleshooting... it's very difficult, for be sure to don't damage the board i've destroy the chip...
inside is all trough hole tecnology... zero smd 

i've also clean the main board and the power supply.
next things to do
-replace the nvram
-clean all the case
-check the fan
-clean the HV CRT board 
-disassembly the front panel and clean the soft button
-reassembly all
-calibrate it
-complete function check

for the scope that doesn't work at all:
there wasn't fuses. i've inser good fuse in it, powered on and.... smell burned electronic   
but for 6-7 second it boot correctly and displayed same error of the other one scope...
so i've open it... disassembled the power supply board and... old electrolitic caps fluid everywhere!!!

so i've desoldered all this NO BRAND CHEAP CAPS (the power supply was OEM from a hong kong company...)
i've also clean the board in isopropilic alcool for 4 hour... now is clean...
i will buy new caps soon...

things to do:
-buy new caps
-solder new caps
-check the power supply voltage
-destroy and desolder the nvram
-replace the nvram
-clean all the case
-check the fan
-clean the HV CRT board 
-disassembly the front panel and clean the soft button
-reassembly all
-calibrate it
-complete function check

--------
soooooooo
little funny "old-stile" things..

all though hole
the fan is "made in we-germany"!!!!!! i think dave will love this... it's before the fall of the berlin wall! great piece of history
the oscillator are from FOX

Faulty NVRAM (non-volatile RAM) causing the issues.
Found a compatible replacement DS1230Y-120+ from Maxim.
Removed the old chip, but accidentally damaged it.
Cleaned the main board and power supply.
Next steps: Replace the NVRAM, clean the case, check the fan, clean the HV CRT board, disassemble the front panel and clean the soft buttons, reassemble everything, calibrate the scope, and complete function check.
For the scope that doesn't work at all:

No fuses present, inserted new fuse, but smelled burned electronics and it shut down.
Booted correctly for a short time and displayed the same errors as the other scope.
Disassembled the power supply board and found leaking electrolytic capacitors.
Desoldered the old capacitors and cleaned the board with isopropyl alcohol.
Next steps: Purchase new capacitors, solder them in place, check power supply voltage, destroy and desolder the NVRAM, replace the NVRAM, clean the case, check the fan, clean the HV CRT board, disassemble the front panel and clean the soft buttons, reassemble everything, calibrate the scope, and complete function check.
Good luck with your repairs!