I would first try to narrow down the problem by identifying the source of the over voltage. GI, lamp matrix or solenoid power will all blow the switch matrix. Try removing the voltage sources one by one and see if the problem goes away.

Start with GI and lamp matrix since they're easy to do and should not affect the problem in other ways. Once you get to solenoid power it gets tougher, but you can segment off sections of the solenoid power and see what happens. Be aware with this last test that you may affect the issue in other ways. For example, the pop bumpers aren't directly causing the short, but the movement of the pop bumper is pulling on another wire and causing the short.

I'm afraid that with any approach other than visual inspection you're going to be blowing more chips.

When you do the visual inspection are you moving any mechanical parts in that area (pop bumper, solenoid, etc.) to see if any wires are getting too close or being stressed?