11 Feb
2015
11 Feb
'15
3:16 p.m.
More recently, I saw a 680k 2W carbon resistor that
read 1.3 meg out of
circuit. As it turns out, it was in a high voltage portion of the circuit,
and I suspect that electromigration caused its failure over time. Many of
you are probably already aware that carbon resistors tend to increase in
value as they age, though there are a few explanations too for that
behavior, as I understand it.
The startup resistors of 'normal' SMPSUs are well-known for failing. They
are typically around 100k and have about 200V across them, so it's not
an over-power issue. It would be interesting to know how they failed.
Perhaps somebody who repairs SMPSUs could keep a few for you.
If anyone has a collection of dead ICs (preferably
those that have died
inexplicably, and not by extreme overvoltage, for instance), I would like
to talk to you about getting a few. If they are 7474s from Texas
Instruments, ca. early 1970s, even better!
ARGH! It is a pity you didn't ask for this about 3 months ago. I had kept
all the ICs I had replaced in HP98x0 machines, these were mostly TTL and
probably some TI ones. Certainly a fair number of 7474s and 74H40s.
Alas I am pretty sure that is one thing I didn't bother to keep and move
to the new house. If I am wrong about that and they turn up here you are
welcome to them.
-tony
Thanks in advance,
Kyle