In article ,
Tiger Luck wrote:

For the record, the amp is in an Advent 300, which I refuse to let die.

Here's a PDF of the schematics:

http://www.davidreaton.com/PDFs/Adve..._schematic.pdf

The cap that blows is C313. It is a 100mfd 35volt cap It is the filter cap
connecting the negative rail in the lower channel to ground. It is on the far
lower
right of the schematic, just above the separate, isolated schematic of the 15
volt
regulator circuit.

The voltage on the negative rail is as it should be. The polarity of the cap
was
correct. The corresponding cap in the other channel does not blow. Both caps
have
the negative connected to the same source from the power supply and both have
their
positives connected to ground. In other words, the negs of both caps are
connected
together to the negative rail from the power supply and both positives are
grounded,
yet one cap blows and the other doesn't. The cap blew with a sharp crack and
the
rubber plug at the bottom blew out. The cap that blew is not shorted. It
still acts
like a cap should when measured with an analog ohm meter. I installed
another, new
cap of equal value and it started heating up, so I cut the power.

I'm not a pro tech, but fairly knowledgeable and good at logic and such.

Any insights?

Part of the circuit might have failed so that it oscillates or pulses.
For example - R313, C305, D301, C309, R335, or any of that bias circuit.
Drag the leads of a big foil capacitor across the leads of C313. It
should spark once to charge it. If it keeps sparking (or smokes),
there's AC current there.

The great thing about stereo amps is that you can put a voltmeter
between the matching parts of each side to find faults.

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