Issue: Everytime a switch from column 8 (grn-gry) is activated, the entire row where the switch resides in is activated as well. This causes havoc to the machine (slam tilts, false scoring...). This is most noticeable on a left flipper press, as the EOS switch causes a slam tilt, essentially quitting the game on a left flipper hit.
Solution: Checked PF for obvious shorts in the column, nothing. All diodes on switches measured ok. Checked Q46 (according to manual responsible for column 8) on the MPU, found it to be defective. Replaced, issue resolved.