I had a feeling it was mostly a belt issue
.
This is pretty much a robust chassis from what I can tell and overall maintenance free except for the occasional belt change.
As for performing an AC3 mod, here are the points.
AFM (RF): right leg of Q352 (right side when looking @ the player from the front)(see pic below for details)
+5vdc: use voltmeter to find as there is no labeling (or see pic below for details)
-5vdv: use voltmeter to find as there is no labeling (or see pic blelow for details)
Mute: pin 10 of CN201 (see pic below showing underside of the audio board)
GND: use voltmeter to find any ground point
Hope this helps