Fosdex multi-tracker / mixer with HDD and CD drive landed on the bench with
the reported fault of "Won't power up. When it last did, smoked"

Once opened, the problem was immediately apparent in that every secondary
side electrolytic on its switchmode power supply, was bulging to a greater
or lesser degree, with a couple of them gone to the point of the top having
split, and spewed electrolyte - the ones behind the reported smoke, I would
guess.

Having noted all the values, I removed them all (13 in total !), in
readiness to do a blanket replacement. Just for sport, I decided to run the
ESR meter over them to see just how bad they were. And this is where it got
odd ...

A couple of them were well out of spec, as you would expect when confronted
by a bulging can, but for the most part, all of them had an acceptable ESR
figure, including the 'exploded' ones. So I got out the capacitance meter
and ran that over them all. This time, almost without exception, all were
low or very low in value, including the two split ones, which were the
better part of open circuit. This was all quite the contrary of what I had
expected. In many cases in the past, I have found electrolytics which
exhibited a very high ESR, but whose value was just about spot on. I don't
recall ever seeing it the other way round though, like this. It's actually
hard to see how a cap can exhibit a perfect ESR, and yet have a value that
has dropped to less than half its marked nominal.

And aside from this, how on earth can every secondary side cap fail in this
way, and all at about the same time? It's not as though most of them are
placed in the designers' favourite spot of next to a heatsink or power
resistor. Neither is the interior of the unit particularly compact. I
wouldn't have thought that the temperature inside the case would get much
above ambient. I can only assume that the caps that have been used, are
either very badly specced, or of extremely poor quality.

Arfa