I'm working on a GNR and am having a transistor problem. Q5 on the PPB was shorted and locking on the automatic shooter coil. So I replaced Q5, checked the diodes on the PPB and also checked the coil diode and the coil resistance. Coil and diodes checked out okay. Powered the game up with the new Q5, coil locked on again. Q5 was hot and shorted again.

So I went back further and checked Q44 and the predriver on the CPU, they tested the same as the other transistors around them making me think they are okay. Replaced Q5 again, replaced the coil and diode just for kicks. Quickly turned on the coil power and it locked on again. Checked the wiring back from the coil back to the board, it had continuity and I could find any exposed wire for it to short.

Should I just go ahead and replace Q44 with a new TIP102 and replace the predriver and try it again even though they seemed ok? Could it be the IC that drives Q44 that has gone bad? I'm not sure where to go from here.

Thanks in advance!

I will check this tomorrow and report back. Thank you.

So I checked voltages at cn6 pin 7. It was 5.07 volts, which seems like that should be close enough. I think I will go ahead and replace q44 and the predriver and see if that works.

Okay, any help would be appreciated. Soldered in a new tip102 and 2n 4401 pre driver on cpu. Soldered in another tip36c on ppb board. Checked everything, diodes, resistors solder joints on ppb, didn't find anything wrong. Even swapped a known good cpu from jp into game, shooter still locks on.

I checked voltages at cn6 and cn5 on the power supply board. So 5v, 12v and 68v were all close. -96v was -92v and the -110 was -116. Is that far enough off to cause problems or is that typical?

I don't know what else to check honestly. Good coil, good diode, new transistors reflowed solder.

Any help would be great, this one has me confused.

The coil is wired correctly and the banded end is toward the larger wire, which is how every other coil on the machine is wired. I've checked, double checked, triple checked. I could cut the diode off the coil and check it again, just for kicks, but I put a new one on there before so the odds are it's okay.