18 Jan
2009
18 Jan
'09
9:49 a.m.
Industry folks say that the lifetime of electrolytic capacitors is
about fourteen years. Since the filter caps in our machines were
significantly (i.e. TWICE) older than that (and some showed physical
Odd... I run machines considerably older than a VAX-11 and have not had
to replace that many electrolytic caps. Yes, I've had the odd one fail,
but by no means all of them. I think I've replaced a couple in HP
desktop calculators and none at all in the PDP11s and the PDP8/e
I would guess I'd replaced many more TTL chips than capacitors in all the
machines I've restored.
symptoms of degradation), we replaced them rather than
deal with them
one by one as they failed. In our experience with our PDP-10 machines,
this was (despite its cost) cheap insurance against periodic failures,
which can occasionally be catastrophic.
That depends, a lot, on the PSU design. Certainly SMPSUs can do some
very odd things if a capacitor goes open-circuit or just high ESR. How
much damage that does to the rest of the PSU or worse the rest of the
machine depends on the design.
I disagree with your opinion on scoping the power
supply outputs. In
my colleagues' work with the PDP-10s we have, they found that 'weird'
problems were often caused by an unexpectedly unfiltered DC line - and
DCOK didn't cop to it. I have clean power - under load - to this machine.
I'll agree with you there. A lot of very obscure problems end up being
traced to {SU problems, either low outputs, or excessve ripple, or spikes
on the output, or.... I always stick a 'scope on them.
-tony