A few notes on a repaired unit. This one had a burnt up speaker, and the power amp IC was shorted to a power rail.
This particular amp has a Tech 21 branded speaker, "Model 2112-A", which has a slightly smaller basket than a standard 12" speaker. A normal 12" speaker will not fit unless the hole is enlarged (enlarging the hole was the official advice I got from Tech 21!). I did not look into reconing the original speaker, but I suppose that is an option as well. I was able to enlarge the hole with a rasp without too much difficulty.
This amp uses a LM3876T power amp IC, clamped to the heatsink. I found it quite awkward to get the heatsink on and off the amp. The order of operations for disassembly appears to be to remove the panel controls, and 5 screws holding the panel first. Leave the rear connectors on until you can remove the clamp from the power amp IC.
A cold solder joint on the V- filter cap caused some interesting effects. On most amps, I would expect to hear loud hum if the V- filter cap is disconnected. On this amp, no noise at all was heard when idling. When played, the 120Hz just mixed with the input, creating sounds the customer perceived as a blown speaker (it did sound like a blown speaker), reminded me of playing with a ring modulator. Perhaps the LM3876T is able to silence hum while idling? Very interesting effect.