How can you be certain an LM3886 is dead?

On power-up, one of my 3886 amps has no signal on the output (except for a buzz which is present on both outputs, but that's for another thread later on...). There is no voltage jump on the output -- just silence.

When swapping the two inputs, the amp is still silent, so the front-end is fine. The only difference between the two amps, other than the silence, is that the LM3886 is getting very hot on the silent one.

Is that a sure-fire dead chip? I built the amp boards with the LM3886T, so switching back to the LM3886TF shouldn't be a big deal because I have the parts. However, desoldering makes me nervous, and I'd like to avoid it if I can.

So before I go ahead with the desoldering pump, is there anything else you think I should check? I've never once fried an LM3875 or LM4780 in worse conditions (25V on the output in one case, and the chip escaped just fine!), so I'm hesitant to just run down this road.

The board *did* work at one point, though. The only changes since the board worked were the heatsink (which probably shorted to the case or something, which would screw things up majorly due to the V- rail being attached to the sink in the back) and screwing it to the case. Oh -- I also had AC1 and AC2 flipped from the other channel, but that shouldn't matter. Other than that, nothing changed.

Any ideas?

Chris

It sounds like you had/have an isolation issue with the case. That issue could also be part of the problem with your buzz. Buzz is usually caused by a ground loop or EMI.

I hope it all sorts out ok for you. Feel free to post some pictures if you want some more advice.

Cheers!
Russ