Hello guys. I have a dr Who that I recently shopped for someone. I have put a new rottendog CPU and replaced connectors j205, j206, j208, j210 and j12. I was very careful to keep the correct order but I've screwed up before! So when I got the game back together it said it was missing 3 balls. I had 3 in it and when I went in test mode and tested the trough switch it registered multiple switches. The switches that show closed are column 2 row 4 (as it should). C 3 R1 through to c3 r3 and column 7 row 1 through to column 7 row 7. If I unplug the j206 connector on the CPU it clears all closed switches. (Other than 2 4). It seems to be a big relation to the opto board underneath the playfield?? The only error it displays is missing 3 balls. I can't say for sure if there has been attempts to fix this before me, I don't think so. I did have this completely disassembled and put LED's in as well.
Thanks

Found it. Diode from a switch was touching a lamp socket! Thanks.