Quoted from bdPinball:Marco on my original thread about the motherboard suggested that it might be one of the 74LS chips that have something to do with the switch matrix. Hell, with all the other chips I've had to replace on this motherboard (I was thinking of calling it a MF board) but yeah- I've replaced the 6502, all three 40 Pin Riots (what a riot that was), and then the 4069, and 4081 chips. That was just to get the board to this point. He gave me some pretty good suggestions on how to test the switch matrix to see if that's getting the "attention" it needs to. Heh.
There is one 74xx chip that the tilt switch passes through. I had one board a while back with similar symptoms until I replaced that faulty chip. It may have been a 7404, but trace out the signal path for the switch to find the chip in question.
[edit]: Ok, I looked it up. It is z26 and the tilt switch goes through pin 13 on the chip. It's 7404 in the bottom right corner next to J3.
I'm guessing if you remove that chip and put it in that $30 7400 chip tester, it will probably test bad.
