With good desoldering gear (likle a Pace solder sucker) you can pull parts
with little risk, if you are careful.
Otherwise, apply a current limited source to the power rails and check the
voltage across each cap with a DMM. The lowest is your first suspect.
-John
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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
