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Ralph Mowery

In article -
september.org, says...

That doesn't mean it could not have high ESR, but it was definitely not the
cause of the problem. There are people who like to change ALL the caps in old
hifi amps, I think they're wrong. While I will agree with changing the
corresponding cap in the other channel when you find a bad one, or even weak
one (significant ESR compared to Xc) it does no good to just change them all
arbitrarily.

Sure it does. If the problem is with one of these caps, changing them
arbitrarily FIXES the problem.

?Penny wise, pound foolish.? Yes, you?re right, finding the ONE cap
that is the cause is technically proficient. But just to say ?I found the
culprit!? does not help the customer (or yourself, if it?s you). The unit
will be back on your bench very soon if you don?t replace all electros now,
if you find one or more below spec.

Unless the capacitors are very expensive, it is best to just replace
them all even if only one or two is showing up to be the problem.

When working a factory repair man came in to repair a 300 HP electric
motor varitable speed drive. This was a 3 phase AC input. He determined
2 out of 3 large diodes were bad. I asked him to replace the 3 rd one
and he said those were about $ 100 each. I said so what, the equipment
beind down was costing several thousand dollars an hour and another $
20,000 to start it up and shut it down. At that ratio of dollars to
production I thought it would be a good idea to replace it even if it
was good.
I am sure it would have started, and may have ran from then on, but why
take a chance it would crap out a week or even a year later.