Amplifier repair problem

I have a Metaxas Solitaire II amp that has a channel that's gone bad. A resistor on the board overheats after a few seconds of turning it on and will fry if left on. The problem is that the unit was professionally modified after the factory configuration so there is no schematic available of the changes. Most commercial repair places have no interest in looking at it when they find out its been modified. Anyone have any suggestions? I would really like to get this repaired. I sure wish I could find out who did the modifications.

Thanks
Nathan