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Carvin PA Amplifier Repair

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GearForGood

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HI everyone, I am new to this site. I have a retirement project called Gear for Good Causes where I accept donated sound and music gear that people no longer want or use or is in need of repair. I fix this gear and then sell it and donate the $$ to registered charities. You can find out more at my website gearforgood.ca

Some of the gear I get is beyond my skill to repair, especially in the area of electronics. I am learning as I go and can do some basic repair work. But there are times I need help from the pros. My latest repair challenge is a Carvin LM 15 PA cabinet that is powered with a built in amplifier. The circuit protect light will not go off. The unit does not make any sound. I have tested the woofer and horn with another amp and they work fine. The multimeter shows that they are running at the correct impedance. I replaced the relay switch that feeds to the speaker outputs. I am wondering if there is any advice about what the likely causes may be? I have attached a schematic. Any help would be appreciated.
 

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It looks like the protection will trip if the average of the two outputs is much away from 0V.

Both speaker output terminals should read 0V, or close to that; when there is any audio out they should swing opposite polarities, so the average stays around zero.

If one is stuck with a voltage on, with no speaker connected, start working back through the power devices and the two driver transistors for each of those, looking for shorted ones?

Or try disconnecting both output transistors on the dead side and check for AC between source and gate connections of each - it's class D, so I'd expect a continuous signal for each device?
 
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