I have a Carver M-400 power amplifier that has died. When you plug it in, you can see a sizable spark at the base of one of the large capacitors behind the power transformer. The amp then pops (if you have a speaker connected) and causes the LEDs on the front of the amp to flicker and jump to all various levels.
I cannot see any components that are destroyed (IE - bulging cap etc), but I have not tried replacing the cap that sparks (because I'm not sure if that's the issue or a symptom).
I bought the amp for under $50 some years ago and have an estimate of a significant amount more to have it fixed, so I'd rather try myself.
Sizable sparks at a cap~ base?? That sounds like there may be a dead short somewhere and/or catastrophic failure of the caps~ (not always visible on the components, use a multimeter to check the terminals if they are shorted.) If there is noting else that has failed in the amplifier other than the power supply* (*if applicable), it is repairable. Otherwise good luck finding the other fault(s)*.
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I have a Carver amp which developed a "hum" also. As a troubleshooting step only (long term this is NOT a solution) you can use a ground plug adapter that removes the ground lug from the unit. This is an adapter that has THREE (Line, Neutral, Ground) female sockets for the amp to be plugged into, and TWO male plugs to go into a wall socket. If the buzz goes away, you've got a leaky capacitor in the Power Supply section of the amp. It will take some doing to actually fix the problem, but this will narrow down the cause.
If the hum disappears when you unplug the input audio cables, you need to use BALANCED lines to the amp. Read up on balanced lines and XLR connectors and TRS connectors. Find the subjects of those on google.
I've owned four of the amps from this series and in no way are the power switches the weakness in this product. (A-220, A-753x, A-760x and an A-500x.) If yours is "broken" it had to be an environmental issue or single unit anomaly if yours hasn't held up. I don't get why people are asking your about the output characterstics of the amp because I don't see anything about THAT in your question. Go to Ebay.com and search for "Sunfire Amplifier" and look for a gentleman who's taken over "Rita's" Carver repair service. They both were affiliated with Bob Carver (you can also search for Bob himself under the seller name "audioshopper") and someone can direct you towards somebody who might (MIGHT) have a NOS power switch available. There have to be a ton of switches that will perform the same function, they just might not be a perfect Chassis fit. There's a solution to your problem. If nothing else, straight wire the switch on and plug the amp into a power strip.
Carver designs in general are not easy to repair. I would recommend that you send this unit into a Carver authorized service center. The likely problem is the output transistors, but the driver circuits and predrivers are not simple designs and if there is a problem there, it could effect the outputs. Tracing this will require equipment and schematics that I don't believe are available on the net.
I found out through the Carver Audio forums that metal shavings inside the case are an issue with this unit. So I used an achohol based spray and cleaned the switchs and the circuit board, (there was a fair amount of shavings found). It has been running for 14 hours with no problems.