Fixed exactly one System one board so far. Had a bad 5101 chip and the buffer chip adjacent the cap? you bypass to get rid of the slam switch circuit which can keep it from booting if memory serves. Very difficult to diag and I got lucky to get it up and going.

Lotta crud/corrosion on those connector fingers that needs to be scrubbed clean with a scrubber for starters, too.

Nice looking game! I would suggest doing the redundant ground mods on the driver board along with the normal ground mod, adding blocking diodes for the transistors if its an earlier revision driver board, rebuilding the power supply as suggested on Pinwiki and checking your sound board for cap leakage (my Totem's sound board had two 470uf caps leak causing damage to the volume pot and other nearby components). That MPU looks pretty good overall.