Alright guys, you get to be my rubber ducky, and maybe someone can see what's going on. I've got a Fliptronics II board that was in a CFTBL. The left flipper was stuck on. Fair enough. I pulled the board, and replaced all 5 LL flipper transistors. Popped it into a different CFTBL here at the shop, and the flipper was still stuck on. Whoops. Looked in the switch test, and sure enough, it was registering an intermittent signal from the left EOS. U5 was already socketed on this board, so I replaced it. No left flipper stuck on, but now, no flippers at all. Flipper button optos register correctly in the switch test. I can stick the old chip in, and get the left flipper stuck on again. So clearly the transistors work. I've tried two brand new chips. Does U1 (marked helpfully as U? in the schematics) actually control if the flippers operate or not? Why, if u1 is somehow bad, does it have no issue activating the flipper with the bad u5? What exactly is happening?