I'm cleaning up and shopping my GI, and took it for a test spin. I noticed that a number of solenoids no longer fire that used to and upon inspection noticed F105 was blown.

I replaced it and turned the game back on. The game would not completely boot up and constantly reset until F105 blew again; after that the game booted up fine. I've looked at a number of other threads about similar symptoms and started checking the 8 coils and transistors associated with F105:

- all transistors check out
- coil #1 (AE-23-800) has a resistance of 0.4 ohms
- coil #2 (A-14701) has a resistance of 4.7 ohms
- coils #3, #4 (AE-26-1200) have a resistance of 10.6 ohms
- coils #5, #6 (AE-26-1500) have a resistance of 14.1 ohms
- coils #7, #8 (AE-23-800) have a resistance of 4.2 ohms
- no visible/obvious shorts

So it looks like coil 1 has an issue. But it's brand new. I just replaced it because the power lug on the previous solenoid had completed separated from the coil. Plus, it's on the topside of the playfield under layers of ramps and plastics, making replacing a b!tch.

Anything else I can test to see what the culprit is? I'd hate to replace the coil again only to have it meltdown too.

I'll check the coil wiring tonight.

Last night the driver transistor (TIP36C, red lead on centre tab, black lead on outside legs) I get a reading +/- 520, which matches all the other solenoid transistors, so I take that to mean the transistor is still good.

Checked the coil diode and it is the short. I checked a few other diodes throughout the game for a baseline and found some other shorted diodes unrelated to this issue (one coil, a few switches).

Based on Borygard's explanation, looks like I installed the coil backwards and fried the diode.

I tested the transistor and it seemed to check out, see post #3.

Now the game now boots up without resetting and without blowing F105, and completed a coil test where all coils fired as they're supposed to.