Just for kicks have you tried a different power supply? You stated you first swapped out the power supply upon your first failure and have had trouble ever since. It's probably unlikely but maybe the power supply is not working correctly under load.

1. Swap in a different known good power supply in there
2. I would replace the transistors and mini transistors in question
3. Cut the power wires to the coils that are associated with the blown out transistors.
4. Test coil ohms with wires cut, and diodes on the coils
5. Power up the game with those solenoids removed and see if anything blows.
6. Hopefully everything is still ok at this point, and then reconnect one solenoid coil at a time and power up after each one and test.

Check the transistor for that coil before installing the new one. I think you are on the right track.

Does the transistor test bad after the coil locks on? You HAVE to have a short in that circuit. For fun (not really fun), remove the connector for that coil off the driver board. Then do a test wire for just that coil to see if it works ok. I'm fairly sure you have somebad wiring either on the connector, the pins on the driver, possibly a jumped solder pad at the transistor for that coil.

Side note, possibly easier. Have you swapped in a different main board and or PPB board that is known good? At least then you can chase it backwards from there. Hopefully it tests fine with different boards. If not then that tells me it's a wiring issue / short.

Also have you retested the voltages at the coil and at all the test points? Could you have an over voltage situation?

Any acid damage to your main board? So sorry to hear you are having so much trouble with it.

Glad I was correct with the jumped solder pad on the driver Congrats on the fix.

Blown transistor, easy fix.

You probably had a weak power supply, got some sort of voltage spike and that took it out. Most likely same cause of all the problems you had earlier. Replacing the power supply should help.

I meant to tell you to also test the PPB board, along with reflowing solder there, just my A.D.D didn't co-operate.

Making pinball great again, one er.. one transistor at a time.