Awhile back, I was playing a game, and started smelling the smoke of doom. I shut the game off, and noticed the right pop bumper had locked on. The coil was so hot that it melted the sleeve! I replaced the coil, as well as the TIP102 transistor, as it was shorted. Powered the game back up, and everything was fine...for a couple days. Noticed the coil lock on again, and I was able to shut it down before it got too hot. Checked the TIP102 again, and one side was only measuring 1.21v. I replaced it, thinking I might have got a bad transistor. I also checked the pre-driver transistor (if that is the correct term), and it read fine. Put everything back together, and it played great. I did all the repairs yesterday, and it seemed to be fixed. Played some games tonight, and low and behold the coil locked on again! I assume it blew a fuse as well this time, as the ball kickout coil will not kick a ball out into the shooter lane. The only thing I have not checked is the coil diode, which I assume is on the aux. driver board, as there was never one on the coil. Is there anything else I should check? And why do these things happen whenever you put a machine up for sale??? (I just listed this last night!) Sigh.

Everything is working as it should, moving freely, etc.

Ok, I'll pull the board out again, change all three, and go from there.

Changed out the TIP122, as well as the 4401. The diode on the aux power supply, D19, checks out ok, so I'm not replacing it...yet. Is there anything else I should be checking?

BTW, the TIP122 was melted this time!!

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I checked the skirt and spoon/switch, all are working fine. Put the board back in, and soon as I start a game, the coil locks on. I thought my soldering was ok, but I guess I need to pull the board again to check it. Starting to get frustrating, so I will sleep on it!

BTW, the fuse is a good idea!

Forgive my lack of correct terminology here, but I've been looking at schematics, and see that besides the TIP122 and 4401, there a 7402 chip (U45) that controls those two transistors via pin 1. I am guessing the 7402 could be the problem here, as it is the only thing that has not been checked/replaced. Is it common for these to go bad/short?