Quoted from HHaase:
I'd check the wiring going into the power supply first. Notoriously bad design for the GI, and more than likely you've got a connector or solder joint going bad going into the power supply.
Yes...the system 7 power supply is really weak in the GI connector area. The power connector to the board burns up, the header pins to the GI strands burns up, and the single fuse holder for all four strands burns up. Lotta burnin' going on.
Some may think it's a hack, but I solder a single large wire in place of the fuse holder, replace the power-to-board connector, replace the header and mating connector with trifurcon (square) pins, and then inline with the harness I solder in a four position fuse holder with a 5ASB fuse in each position, isolating each GI strand. Later Williams games have a similar setup.
Also BTW...why is there no Firepower 2 club thread? I don't own one but I know it's different enough from Firepower that discussing both in the same thread can get confusing. System 6 vs. System 7, different playfield, artwork, gameplay, part #'s, etc... ...perhaps someone well-versed with FP2 should start a club thread for it?