Amplifier repair possible? Getting hot

I have two 8 gauge wires, connected to a positive distribution block connecting the two amps together, running directly to the battery, so they are not really running of the same power wire, and I have tried installing the bad M25 where the good M50 is located, and it does the same thing.  I am pretty sure that it is internal, and hoping someone could tell me what could be causing it.  I am testing resistors, and diodes, but not too good with transisitors, and capacitors and such, and was just hoping someone could tell me what type of component on the circuit board could give this type of problem.  It is apparently somewhere between the power supply and the transistors mounted to the heat sink, as the heat sink gets extremely hot, and looks like it has nothing to do with the speaker section of the amplifier.  Keep the advice coming, thanks.