Weird problem on a Gorgar I just picked up. When it's powered up it acts like it's in audit mode but just continually rapidly scrolls through the audits. The credit / ball display shows 04 in the left display, the right one scrolls from 1 through 35 (I think), while the player 1 display scrolls through the corresponding audit / adjustment settings. I does this if the middle service switch is in the up position, if it is down (or if that connector is unplugged) the game wont boot at all. Anyone have any ideas before I dig deeper into it? I haven't replaced any chip sockets on the MPU yet since they are not Scanbe and look okay. I tried it with a different known good driver board just to rule that out, no change. Also burned a new set of flipper / game EPROMs, no change. And tried swapping the NVRAM with a 5101 RAM chip, no change.

That was it! The ground where it travels from the front of the board to the back through one of the battery pack mounting holes was bad. Stitching a wire through the hole fixed it. That looks like it could be a pretty common problem, I'm surprised I haven't run across it before. Thanks so much for the help!!

Thanks barakandl for pointing me in the right direction, and thanks for all of the other suggestions. Another mystery solved!