Hey guys, did a little hunting around for a similar thread and couldn't find anything, so I figured I'd start a new one and see if anyone has seen something like this. I installed an led light kit on our junk yard, after I was finished I played a game, made it to the second ball and all hell broke loose once I hit a ball into the sewer! Basically if the fridge VUK fires all the switches on the matrix close. If I unplug the coil the switch problem disappears, but as soon as I plug the coil back in, it fires and all the switches close. Tech alert says all rows are shorted to ground. I unplugged the switch rows and columns at the CPU board and the problem persists. I checked the transistors and diodes in the power driver circuit relating to the fridge vuk, and everything seems okay.

Any Ideas?

I did indeed have the power on while doing the LED kit. I had never heard that this could cause problems. With as much of a pain as the wedge led replacements can be (having to fuss with the wires to get them to make good contact) I've always changed them while in lamp test mode. Well, good to know anyway. I will look at U20 in the morning, thanks for the replies!

How can I do a lick test with the power off?!?

just kidding, you are correct, and in most cases I do, but it never occurred to me that an led kit could damage a game.

I did all of the gi bulbs from the top, the game needed a good cleaning anyway, but what you said got me thinking, and you know what? I had to unscrew a couple of the gi bulbs from the bottom to get the subway track out, one of those could have easily touched something.

Let me clarify. On our junkyard there is a molex plug right by the fridge coil, not sure if that's like that from factory or if it was added by us for some reason. When that plug is unplugged, I do not have the problems with the switches shorting out, when I plug it back in it starts freaking out. Separate from that, when I unplug the switch rows and columns from the cpu board, I get the same reaction, which leads me to believe my problem is on the boards and not coming from a short in the playfield wiring.

Hey everyone, swapped U20 and that took care of all my switch problems, thanks to those that chimed in!