^^^ What he said ^^^
There is no service information available on the factory amp that I am aware of (tho I could be wrong, if you were 'plugged in to' the industry, mabye) and no easy source of parts. Added to that, actual component-level electronic techs are rare; you won't likely find one. And at $75 an hour and up, you can source another one on eBay for less than the repair.
My bet is that it is that Apline head unit. Should have bought a Kenwood!
Pizzaguy
aka
Mark Christopher
KenwoodUSA Corporation
Systems Division
Suwanee, GA