Hey folks, happy just-after-turkey day!

Running into an issue post-surgery on my High Speed MPU. Background: Transistor Q73 burned itself up (thing looked like a roasted marshmallow), so after pulling the MPU I determined Q72 and Q73 dead. The resistors R105, R106, & R107 were also not measuring correctly (when compared to the others for these similar transistors). So I replaced the transistors & resistors. My replacement resistors are series chains of 2-3 resistors to create the appropriate resistance. After I installed these too, everything looks good except for R106.

R106 should be 560 ohms. Before I installed my new ones, I verified it was good (I put together a 330 & a 220 so it measured about 550). After I installed it, however, it's only reading about 47 Ohms. I removed it again, thinking I'd screwed it up somehow, but then after removal I measured it again and it still reads 550. What's happening here? If the other similar resistors (e.g., R109, R103, etc) were doing this too, I wouldn't be concerned, but they're not. Why is it dropping so much, and what do I need to do to fix this?

Alright, well I guess I'll see what happens then when I hook it back up in the machine. (Still have to replace the coil that locked up too.) Just seems suspicious that all the others in this area measure differently than this one. I'm concerned there could be some sort of damage to the board. That transistor got ROASTED. (It happened during a party and I wasn't nearby, then when I got nearby enough to smell electrical fire, sure enough moments later smoke was coming out of the backbox.)

Anyone else with a High Speed that could verify what resistance they get across R106?

Good suggestion, though I'd cleaned the board pretty well before I did my surgery. Important tip for anyone looking in the future.

Oh boy, thanks to your user name, I get to use one of my favorite memes:

Good-Job-Dumbass (resized).jpg

^^ Winner winner chicken dinner! Last time we replaced some of these components, we socketed U45 for easy R&R. Luckily I had one extra chip for U45 so I just popped the old one out and dropped in the new one. Voila, R106 now reads correctly!

I was trying to find some root cause of the transistor (& bumper coil) burnup ... since I had to rebuild the coil setup for the right pop bumper, while I had it torn apart, I looked at it more closely. The switch was very tightly gapped, which is normally ok -- except, when in a certain position, the skirt was getting stuck and holding the switch closed. I made some adjustments and did some cleaning and it doesn't seem to get stuck now.

Coil assembly rebuilt, and board surgery complete, I reinstalled the MPU and the game now plays fine!!! Whew. It's been down for almost two months now because I haven't had time to work on it. Playing one game on it just now reminded me how much I've missed it!

Thanks for the help all, especially DumbAss!