If you haven’t already, I’d open the game and locate the coin unit and the player unit and at least watch these “stepper units” as they operate. Note there are rivets which get contacted at various positions. And with power off, you can manually actuate their plunger to understand their incrementing operation. The coin unit will also have a plunger to fully reset the unit. The player unit only increments. Are they sticking/sluggish or are they pretty smooth/snappy?

Like Howard says, start with the coin unit and watch it as you add players at start of game. Does it advance properly (only) one step for each added player? It’s only job is to define the # of players for the current game, so it does not move during the game once all players are “coined up”. Let us know what it is doing.

The player unit is more complex. It keeps track of what ball is being played. Therefore it increments between each ball. It is also wired to manage the active player. 20 of its sequential positions define the 20 total playable balls for a game: Player1-ball1, P2b1, P3b1, P4b1, P1-ball2, P2b2... P4b5. It skips past unneeded positions when # of players is < 4. The ‘add “player” unit’ at left of Howard’s schematic is the coil that increments the player unit. Do not confuse it with “adding players” at coin up.

Here’s a video showing some stepper units. Your coin unit is a total reset stepper like he shows starting at the 2:00 minute mark:

Studying the mechanisms will help you understand them. In time the schematics will make more sense and the two worlds (mechanisms vs. symbols) will become one.