signal proccessor problem

I just bought this amp as a repair project hoping to just replace a few transistors and maybe a few resistors, but nothings fried. some sound comes out quiet and distorted through the pre amps when its on its open or lp x-over settings. the output is still quiet but clear on the hp setting. and the line inputs are clear of distortion but still as quiet. I,ve looked it over and theres no toasted transistors,diodes,resistors,capacitors, or tracers, but I'm sure that theres a bad diode or IC. I figure that my signal proccessing is screw'd up and wont allow the transistors to switch the mosfets properly. this amp came out the box and worked for 2 weeks on a 4 ohm, 2 ch set up with a 2v preamp and the x-overs set low on the amp and head unit both. and the previous owner had it installed and set up at a proformance audio shop. I'd hope to get it working and would consider sedding it in (if only it was under factory warrantee, huh?). I enjoy repairing things but I do need some help with this one.:bawling: