problem with powerball in Twilight Zone

[Chad]

I checked the wiring all the way to CPU board & it looks & meters ok. I then placed a short between pin 5 of J206 & pin 8 of J205 (on the cpu board) which is the output for the slot proximity board but this did not activate the powerball mode. So now I assume I have a problem with my cpu board, does this sound like the right way to test this cct.

[Chad]

I managed to fix my TZ today, it appears the problem was SW 51, when measuring this switch it won't show 0 or infinity ohms but very high resistance (this was also shown as an error - SW 51 Gum Popper Lane ), I operate the switch a few times & then I was able to measure 0 & infinity ohms. I then played a few games in which the powerball was detected & working as it should. I look at the switch matrix & found that SW 51 shares the same column as the slot proximity. I assume the switch must of being dirty or stuck in between on/off & will probably need replacing in the near future.
Thanks to everyone who provided help.

[pinball god]

Ill note this solution for future ref. Thanks