I'd thought about that, but the odd thing is that it doesn't seem to matter 
what time of day the test is started - the op amp just seems to take a long 
time to latch up.  I don't think it's thermal: the lid is off, the 
components are cool.  Curiouser indeed.  BTW, it does seem to be the 
"phase-inversion" type of latch-up, resulting in significant power supply 
draw.

RR

> <respectful snip>
>
> Hmmm, 22 hrs for the fault to appear? Methinks this is a big, BIG clue....
> I'm suspicious of something wrong externally, like a piece of equipment
> that kicks on
> when the office gets cold, or an arc in a phase-correction box down the
> street, or
> maybe cellphone interference...?
>
> "Curiouser and curiouser", said Alice...
>
> --Bob
>
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