bram stokers dracula. In switch test with all connectors removed from the bottom of the cpu board. Using jumpers and diodes, if I activate any switch in row 1 and any switch in column 1 at the same time, I get those two switches plus the corresponding "battleship" switch. I mean if I use the 3rd switch in each I get the 3rd in and 3rd down on the matrix. First problem was a ground short and I have replaced U14, U20, and U18. Now this crazy stuff
Each switch will work properly if activated separately, and only combos of row 1 and column 1 cause the third switch register. None of the other rows or columns will cause this to happen. Any ideas?

Original.

That's what first caught my attention after the repairs. The castle up kicker would pop occasionally when the drop target was down. I thought if was a flaky opto but switch test confirmed the "battleship" switch firing. Row 1 was shorted.

No I don't.

Sorry, I had to re-read my first post. I replaced U13 when I replaced U18. But all pins read ok. Inputs and outputs are different but consistent.

Could it be the ASIC? How often do they fail?

Yes, U14 was replaced.

I replaced them thinking they were at fault for the intermittent popping. After that I got into switch test and found the "battleship" switches were registering any time row1 and column 1 were held in. ie, if I hold in switch 21 and 17 I get them and switch 27.

Had some time this evening and dug a little deeper. When in single lamp test I get a light (LED) in another row other than the selected lamp.
A logic probe shows a high on column 1 at J137 pin1, even when the other columns are selected. The selected column goes high and stays high when its lamps are strobed. Weird. Also found that if I remove the ribbon connector between the cpu (original williams) and the driver board (rottendog) my switch malfunction goes away and all switches work correctly and independently without the "battleship" phenomenon.
Maybe something on the driver board messing with the D0 line?

Not sure. It was a coin taker kit. I'll try some different leds tomorrow. But what about my switch problem going away??

I don't have one but I think I can borrow one from a buddy for over the weekend.

I didn't replace any chips on the driver board. I'm working on getting one to swap out....

I'm wondering if when the ground short occurred that it weakened the ASIC to the point that its fan-out has diminished for the D0 line??
Any thoughts?

Yes I did. Standard procedure here also. I also check pin to pin on a chip and continuity to the next chip also. But the problem goes away when the ribbon cable is disconnected.

To quote one of my favorite pinballs, "We have a winner" U7 pins 4 and 5 weren't shorted, but definitely had some conductivity. After removing U7, the switches and lamps are functioning as they should. From the schematics I found, U7 and U8 are useless. J109 and J110 are not used. Or did I miss something?

Thanks to all who responded to my post!!

1 billion 4 and change! Not bad for a 3 ball game if I do say so myself!! Working real good now. Thanks again for all the help.