Diagnosis & Repair update :-ditched the extra iso
-installed new fuses
-pulled all boards
-cleaned inside
-cleaned dirt off power block
-installed new ROMs on MPU
-visual inspection of MPU (checks out)
-visual inspection of other boards
-cleaned all connection pins on boards
-replaced capacitor on power supply
-reinstalled all boards
-attempted to test power supply (but instructions on PinRepair can't be followed since they refer to an upright pin power supply which has a different layout)
-reconnected all boards
-On power up, everything seems same as it was before:
Some lamps are lit, I hear something click once but can't figure out which solenoid it would be. MPU LED not lit, does not flash. Score displays are blank. Test switch does nothing. Reset switch on MPU does nothing.
Also: ball outhole solenoid is burning up (but it's not in an activated state)
I'm stumped.