Electronics > Repair
Agilent 53132A Counter Repair (FIXED and Upgraded)
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richard.cs:
Bumping an old thread... I figure as this morphed into a general repair thread over 3 years it can do no harm and I could use some advice from people who've had them apart.

I have a HP53132A that was a skip rescue, it was working perfectly, though I had not used it very much. This evening I go to turn it on and the front panel flashes and internal relays chatter continuously. I am thinking PSU problems causing it to power cycle when the load is increased (the rear fan runs fine in standby, doesn't slow noticeably when I try to turn it on but it's rather hard to tell with all the chattering). Sound plausible?

I see there's not a great deal of detail in the service manual, it being geared more towards replacing modules, though there is at least a set of testpoints and target voltages. I don't suppose anyone found further details than that? I've seen schematic snippets in this thread, some reverse engineered and some looking like they come from HP/Agilent documentation. Of course I may yet find an obvious failure when I crack her open, but it's 22:30 here so that's not going to happen today.

I suspect it may well have had some rough treatment before I owned it, but it's been in (very) occasional use for a couple of years without problems.
HighVoltage:
Did you test all power supply output and especially for any ripple on the dc rails?
richard.cs:

--- Quote from: HighVoltage on May 13, 2020, 10:01:53 am ---Did you test all power supply output and especially for any ripple on the dc rails?

--- End quote ---

First thing on my list to do, hopefully I'll get a chance today. Is there a target ripple specification, the service manual only gives DC tolerances.
richard.cs:
It's very clearly a PSU fault, the supply voltages are low in standby, and fall further and become noisier when I turn the instrument on.

SupplyStandbyOn5V3.5O2.4+12V10.610.1-12V-11.9-7.3-9V-8.9-8.9
Overall it's quite dusty inside and in need of a good clean, but there is no visible damage (no domed caps or visible heat damage apart from perhaps a slight PCB yellowing near Q1).

The -12 and 5V seem to be the worst offenders, with +12V being out-of-spec but not dropping much at switch on. Looking at the schematic Jf2014 posted, likely candidates would seem to be the primary current sense (R5) failing high, problems with the aux supply (D2, R4, etc.) causing cycling when more gate drive power is demanded, feedback problems, etc. I am not sure I quite understand the whole circuit* but there are some interesting features in there like making the current sense dependent on primary voltage. I'm not quite sure what IC3 is about either - cleaner shutdown when power is removed?

*What's that complex arrangement on the bottom left? I know it's one of the controllers where V(comp) sets Ipeak, but the role of Q22, Q23, Q24 does not seem clear to me.
HighVoltage:
That is a very good start for the repair.
Most likely one or more components are pulling too much current.

Just follow the current path and remove a possible suspect and see if the voltage jumps back to its normal values.

Unless the problem is within the power supply rails, check that first.

You should find the culprit easily.
 
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