Even with a full schematic, the requirements for the main processor
to keep the line relay closed and running is not obvious.
Two of these cycles from O/I switch latches the unit off until
line input power itself is cycled.(There is a dual flipflop in the
housekeeping circuitry).
All supply lines are monitored to develop 'power good', but there's
no obvious power circuit failure evident during the period of relay
closure - except that the front panel doesn't even blink.
All service troubleshooting involves interaction with the front panel
display. . . .with specialized harness extenders and board
substitutions.
The harnessing is nuts, with signals routed through 4 or 5 cards and
connectors before arriving at their destination. I expect the
organization of power circuits and control logic will be similarly
convoluted.
I've told the owner - no repair / no charge - take it to Yamaha
service - but it hasn't been picked up since.
RL