Can you scan and email this part of the schematic?

Ive only worked on 2 player Bally EM's,

Player select is in the backbox from 1 to 2 player... you might have 4 of these in your back box or 2 off 2 way relays to transfer from 1&2 player and 3&4 player... need schematic and pic inside header..

I'll try mate. The Schematic is around 10 X the size of a GTB Wedgehead, but the relevant sections should be scanned ok

Could a stepper unit be one increment out of correct position?

I thought it was the player unit. I rebuilt it as part of the restore. It is adjusted correctly. I checked again a couple of days ago.

Have you tried moving the stepper unit in the back box by hand? It could be that it is dirty or binding on something and that is causing the skipping. One was dirty in a machine I worked on and I had similar results.

All steppers are rebuilt. It seems like it is more of a contact adjustment issue.