Failed ICs and components

tony duell ard at
Wed Feb 11 17:16:35 CST 2015

> 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.


Thanks in advance,


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