5 Mar
2005
5 Mar
'05
5:57 p.m.
I have a couple of questions that I haven't been able to find in my books.
(1) there has been much discussion in this list about capacitors failing. I
recently had a cap on a QIC-24 drive fail with a bit of sound and fury (axial
tantalum). Is there any way to test for this other than desoldering every cap
Yes, tantalum caps are good at that. The good news is that there's
usually no other damage.
(at least every electrolytic) and testing it on a cap
meter? I don't want to
fry my IMSAI, but there are a lot of caps in there and it would take forever...
Cehck for dead shorts ebtween each power rail (at the output of each
3-terminal regulator on each card) and groud. These caps fail shorted,
which is why they generally explode.
I would be more wary of the big aluminium electrolytics in the PSU. If
one of those goes up you'll know it. I would reform them (bench PSU and
series resistor, there must be a FAQ on this somewhere) before powering
up the machine.
(2) (flame risk) My Tek 555 popped and blew a fuse when I had it plugged in
last. I disassembled the PS and cleaned off the dust, and I want to test it by
itself, but the power-on relay won't close. Any hints, or is this like
amplifiers where the tubes need a load?
It's getting late (too late for me to hunt for the service manual), but
from what I remember you need to have the 'scope
connected. The heater
transformer, for example, is in the 'scope, fed with
controlled AC from
the PSU box.
-tony