looks as if you and i have similliar problems.From the sound of things,or lack of!!. except for one important factor,Your discription supports a theory that i have been working on for some time now, that some or possibly all of the important STUFF THAT KEEPS THESE IC'S RUNNING SMOOTHLY, YES, I HATE TO SAY IT BUT THE SMOKE WAS RELEASED!!!. sometimes it can be very tricky trying to recapture that smoke!!. I will be keeping an eye out for your schematic. I have an ORION 280gx 160 WATTS RMS. I am missing the pigtail, plus my brother tried tapping in but could not get it to work. I think i might be a bit more fortunate than you, i believe i still have all the smoke. thank goodness.
GOOD LUCK TO YOU