Using a Variac to revive power supplies
ard at p850ug1.demon.co.uk
Sat Dec 25 06:03:50 CST 2010
> Nasty things exploding capacitors. Engineers dictum "If in doubt chuck =
Although modst modern capacitors (read : anything you will find in a
classic computer) have vents or deliberatly weakened sections of can so
that they will fail in a relatively safe manner. Still unpleasant.
> out" ie replace. We used to reform supposedly new electrolytics if they
I don;t normally replace working components, but I did replace the pair
of mains smoothing capacitors in my HP120. They tested fine, but the tops
of the cans were bulging. The position of the PSU board is such that they
were pointing straight at the CRT neck. Had one failed, I suspect it
would ahve broken the neck off the CRT. Now, while that is unlikely to
cause a violent implosion, new CRTs are much harder to find than
smoothing capacitors, so I repleaced the latter before any harm was done.
> been in the stores for a while.
If a cpacitor refroms and has a low leakage, etc, then it should be
perfeclty OK to use. After all, reforming is just redepositing the
dielectric oxide layer, and that's how they were 'formed' originally.
Perhaps I have just been very lucky (or only work on well-made machines),
but I do not find smoothing capacitor failure to be as much of a problem
as some people seem to think.
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