I figured out how to get into the service menu, thanks to someone on this video:
I only tried turning the 'pin amp' up and down from the original value to see if it would change at all, and of course it didn't.
I see in the circuit diagram q551, 2s02394-ef PIN OUT. It's fed from pin 5 (E/W OUT) of IC301, VDP3108 DECODER IC.