Dave,
Based on your reference to having multiple vertical mounted caps I would assume you are talking about a SMPS.
Personally I would not restrict yourself to the capacitors alone. Typically caps are the highest failure items, but based on my experience any resistor in the HV side is also a likely suspect, and if fuses blow then you need to check anything silicon along with GDT's and MOV's if they exist in circuit.
The following reference is an extreemly comprehensive guide to repairing SMPS's - after reading it and applying its principles a few times I no longer fear SMPS's as I used to.
In addition to the series light bulb trick, I suggest you disable the main switching transistor(s) by removal (and test when removed) to eliminate primary side or secondary side issues.
PS. I highly recommend you invest in an ESR meter - even for the sake of eliminanation os any likely suspects.
--
Wayne
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--- In hp_agilent_equipment@..., David Speck <Dave@...> wrote:
Looking over the list, I have noted that the majority of problems with
old equipment is failure of the electrolytic capacitors in the power
supplies over time.
I wonder if the veterans can offer any suggestions on their favorite
techniques for finding bad caps in circuit, especially those that have
not been so considerate to have blown their end caps off or otherwise
developed obvious physical failures.
I have a critical undocumented circuit board of relatively recent
construction with about 25 vertically mounted axial lead caps. It's
begun eating fuses at an increasing rate, and now, even a 2 amp fuse
blows instantly in a slot intended for a half amp fuse. No way to lift
one lead of the cap without pulling it out of the PCB, with the
attendant risk of ruining the irreplaceable board. (well, I could
replace it for another $6-7,000, but that's not in the budget this week!)
I figured I could put in another 2 amp fuse, and run it on a Variac at
reduced voltage while watching the current consumption, and see what
component heats up, but I really don't want to trash the microcomputer
on the board.
Any one have suggestions for any specific low voltage instruments for
in-circuit cap checking, or home-brew gimmicks that one can work up, to
give better information than the typical DVM and scope?
Thanks in advance,
Dave
