Re: Power Amp Repair

Haaky wrote:
I need some advice guys.

I have an American Audio GX-300 Power Amp i use in my studio. Bought
it used off of EBay. Been working like a charm for almost a year. One
day while tunning up a guitar the amp shut off. Found it blew a fuse.
I replaced the fuse switched it back on and it blew again.

Finially had to take it in . I was told that an Output had gone. Cost
me 140 bucks Canadian to replare it.

I get it back a week later. Take it home, plug it in. And bang the
fuse blows again right away. I return the amp to the repair shop. 2
weeks later i get it back. They told me the Output the guy replaced
was fautly and get this he wanted more money to fix what was suppose
to be fixed properly in the first place.

Any i get the amp back, worked fine for a week. Then 1 day i turn it
on and it pops the fuse again. I replaced the fuse and it worked fine.
A week later turn it on again and it popped the fuse again.

I'm not taking it back the the these guys again. I'de rather try and
diagnose the problem myself and fix it.

Any ideas to where and what i should be looking for and were to start
looking for the problem?

I've been doing alot of research and am comfortable with electronics
to try and narrow down the fault and fix it.

Any help would be greatly appreciated. If you need any more ifo i can
provide it. I also have the schematics for the amp aswell. That was a
bonus courtasy of American Audio Inc.

Let me suggest that perhaps the idling current is set too high. Then the output transistors start to warm up and after a while there is thermal runaway and the fuse pops.

Check the idling current and adjust it if needed. Another possibility is that the temperature sensor, usually a transistor or diode or thermistor, is not properly attached to the heat sink and thus doesn't react to warming output transistors.

Bob
.

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