Quoted from frunch:
That section of the board is where the mpu handles the coils. I'd be wary of coil voltage shorting to 5v somewhere (and quite possibly over-fused). Do the coils under the pf look okay?
While the j4 connector is where the solenoid signals are sent to the solenoid driver board, they are 5 volts signals. The solenoid driver board grounds the +43v that's sent to each coil directly from the rectifier board, through the under playfield fuse.
The +43 that goes to the mpu board is just for the zero crossing signal - nothing else.
As for the board, ouch. I'd buzz out the carbonized mess to see if it's conductive before deciding to do anything else with it. Going to be difficult to save that one.