As ArgosySK and kguenther6 wrote about, it is most likely that your coin unit stepper is not resetting properly and the spider on the back side is not rotating back to the 1-player position at machine bootup.
Below are rough pics of a typical coin unit from a Williams 4 player machine of your vintage. The first 2 photos depict the spider side of the coin unit in the 1-player and the 4-player positions, respectively. Note than in the 1-player position, the longer arm of the spider is oriented pretty much straight up at 12 o'clock, while in the 4-player position, the same arm of the spider has rotated counter clockwise by 4 steps on the copper trace. The 3rd and 4th photos depict the gear orientation at the 1-player and 4-player positions, respectively.
The peg and switch referenced by Pinballdaveh are seen in the lower left quadrant in the 3rd and 4th photos. That switch, when opened by the peg from underneath, effectively disables the credit button from wasting credits if someone mistakenly tries to add any more players when the stepper is already at the 4-player position.
The coin unit stepper gets reset by a clockspring around the gear shaft that gets wound up when multiple players get added. When the machine is booted up (first for one player), the reset solenoid plunger pulls in and pulls the stop away from the ratchet such that the clockspring can rotate the spider/gear back to reset position, but sometimes, the stepper mechanism and gear shaft get gummed up and the clockspring does not have enough force to rotate the stepper back all the way to reset. This failure can also occur if the peg mentioned in post 2 gets on the topside of the switch on the gear side.
As kguenther6 was suggesting, you can check for free movement by operating the coin unit stepper with the game off by manually depressing the plungers on the advance solenoid and the reset solenoid to determine of the unit is advancing thru players 2, 3, and 4, and then resetting back again. If not, you likely have one or more of the following:
1) gear shaft is gummed up and sticky.
2) spider arms on backside press down on the traces with too much tension (increased friction) and could use to be adjusted.
3) copper traces need cleaning and a very light film of teflon lube to reduce frictional forces.
4) Someone perhaps unwound the clockspring by 1 or 2 turns, such that it does not have enough tension to fully reset the unit.
Lee
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Canton, OH
Regina, SK
