Acoustic 220=speaker killer

[MstrB]

Hello, another Acoustic Control amp. This one killed its speakers. Looks ok on O-scope, I thought bad voltage showed a vertical but its been a long time since I had to work on SS. With no signal it is heating up the load resistor so must be throwing something. I have a schem but it is hard to read, very blurry. Any help would be appreciated, jog my memory on SS.

[Mars Amp Repair]

First of all, I wouldn't run it on a load until you have the DC offset gone. Most likely your power transistors are fried...you can determine that with a simple ohmeter.

You probably also have other drive related transistors bad, too.

anyway, that's a good place to start...glen

[MstrB]

The owner (a friend) told me he had played through it for a short time through a different cab when he bought it so I mistakenly thought the speakers died from a different source. When the amp looked OK on the scope I added the load resistors and found they heated up.

[Enzo]

Is there DC across that load resistor?

WWithout me looking up the schematic, is this like most Acoustic amps in having a single power rail? A shorted or very leaky output cap would put DC on a speaker. WHich would burn it up.

[drewl]

And if the scope is set to ac coupling you won't see the DC screaming out of it.