Before you go soldering in a very expensive power driver board, eliminate it as the cause : remove the ribbon cable between the CPU and Power Driver PCB, and retest the switch matrix.

BTW, the ONLY switches that come from the Power Driver PCB are Left and Right Flipper, and those were only used for FunHouse, Bride of Pinbot, and the other WPC games that predated Addams Family (and FlipTronic).

Ok, so if the switch issues only occur when the power board ribbon cable is connected, then yes - you're on the right track with the LM339. That is what detects the optocouplers that in turn detect the flipper switch activation (which is not used on this game). It connects directly to the switch row lines.

WMS uses LM339s *everywhere* ... on these inputs, on the zero crossing detection, on lamp matrix row returns, on switch row returns, on direct switch inputs, on fliptronic flipper switch inputs, on opto driver boards, on ...

well, you get the idea.

LM339 is used for the old-style flipper switch detection ... basically, when the cabinet flipper switch is pressed to engage the flipper, the current for the flipper coils passes through an optocoupler.

this optocoupler is then connected to a LM339 voltage comparator which, in turn, is connected to the switch matrix via the column/row signals contained on the CPUPower Driver ribbon cable.

These row returns, along with Zero Crossing, are the only signals that are returned to the CPU from the power driver ... everything else is a one way output only signal.

Anyways - this makes that circuity very easy to isolate : unplug the ribbon cable, and it's isolated.

Yeah, all the lamps/coils will go dark, but if you're diagnosing switch matrix issues, you don't care about that stuff anyways.