Electronics > Repair
HP 54502A repair once again
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vanhouten:
Hi everybody,

my HP-54502A quit from working just a few days ago.
When I got it long time ago it was at least booting and after installing a fresh NVRAM (Dallas-Model) on a socket it turned on again and has been working since with the first auto-calibration.
Now it fails again on me in that in won't even boot 99% of the times.

Here are the symptoms I can recognize:
-> Very sporadically it might turn on normally but only to die again after a few seconds.
-> The fan is slightly moving periodically but will not start spinning
-> thers is a clicking sound coming from near the main transformator of the PSU
-> there is a little less audible clicking from the opposite side near the CRT.
-> voltage test points on the PSU show anything but the values proposed in the service manual
    (which recommends replacing the PSU altogether :()

I have read some similar behaviour in another post, yet there was no conclusion as to what the actual reason might be.
Does anyone have had similar behaviour or an idea, where to start diggin on this one?
I would like to avoid selling it at a bargain-price because I consider the scope to be mostly intact besides the mentioned flaws.

Any idea would be very appreciated.
Thanks a lot for yout time reading this...

Best regards,
Fab
tautech:
From the first post in the Repair thread:
http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

The clicking sounds like a SMPS failing to start. Does it use a SMPS?
Start digging in the PSU's LV & HV

Any Tantalum caps on the PCB's?
wn1fju:
Yup, sounds like a power supply fault.  I believe the switching power supply used in the HP 545xx series is a Boschert model.  Someone years ago reverse engineered the thing for the 54503A and the hand-drawn schematics are at http://www.radiocollection.be/images/restaurations_img/HP54503/supplyHP54503.pdf.  This supply is used in a lot of HP models, not just scopes.  For instance, I had one in an HP 53310A modulation domain analyzer.  For what it's worth, I was ultimately unsuccessful fixing the Boschert supply I had, which included replacing all the electrolytics (7 of them had leaked goo) and the main switching transistor (several times, I blew them up).  Finally, in desperation, I bought a "non-working" HP 1650A logic analyzer for a few bucks since it had the same Boschert power supply.  But alas, the 1650A actually worked, so after I pulled the supply and verified that my 53310A was working, I put the good supply back into the 1650A.  Bottom line:  I finally bought two Meanwell switching supplies and built my own power supply for the HP 53310A.  Works like a champ, draws only about 80 watts instead of Boschert's 120 watts and cost me less than fifty bucks.
KJDS:
It's interesting to learn that the 545xx series uses the same power supplies.
Wuerstchenhund:

--- Quote from: KJDS on October 22, 2014, 05:29:53 pm ---It's interesting to learn that the 545xx series uses the same power supplies.

--- End quote ---

They don't. The 5450xA/54510A/54520A and some other models use the same PSU (Boschert). The 54522A/C and 54542A/C use a different PSU (Artesyn/Computer Products XL130-3630E, now it belongs to Eaton). And if my memory serves me right then the 54510B/54520B (and maybe some other models) use another model of PSU.
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