MTX THUNDER 6304

Ok, I'll take some pictures, but I've already removed what was burnt and cleaned the board.
It could be something else burnt, which is why the MOSFETs in the power amp excitation transistors burn out. It could be the REC602 and REC601 diodes and the 8200uFX35V capacitor, which could be the problem. But try to post pictures, ok?
 
I'll wait until I can see what you have but you should (virtually), never burn an FET when testing. You either use a current limiter (I prefer a large 2 ohm resistor) or insert a low-rated fuse (more costly) but you always tightly clamp the FETs to the heatsink when there could be a problem. Add to that, you virtually always confirm that you have a good drive signal (properly loaded) before installing the FETs.
 
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