I have the schematics and I've read through a few threads here about how to read schematics, but I'm still clueless. When player 3 drains a ball, the solenoid in the backbox never seems to get power to advance for player 4 (although if I press the solenoid manually it does advance). I assume this means I likely have a broken or disconnected wire somewhere, but I have no idea what I should do to find that broken connection. I know I should probably jumper some other connection as a test, but I don't know where to begin deciding what to jumper. Any help is GREATLY appreciated.

Thanks everyone for the replies. I’ve checked the P relay (easiest for me to check since the play field is up). It behaves the same after the ball drains and trough switch is pressed for each player. Next I’ll check the player unit although it’s a bit intimidating with all of the switches.

I’ve discovered that if I flip the out hole and trough switch on player floor without registering any score for player 3, the player unit will correctly progress to player 4. If player 3 scores any points, the player unit will not progress to player 4 if the ball is drained. I’m not sure what that means or where to look for the problem but maybe one of you pinball geniuses can point me in the next direction?

Any points. To test, I have the playfield up, so I've been tapping the bumpers next to the flippers a few times, then tapping the outhole switch and the trough switch to advance to the next player. The strange thing is, if I DON'T add any score on player 1, then I can't advance to player 2, but if I DO add score to player 3, then I can't advance to player 4.

When I get stuck on player 3, if I drop coins and press the button to add players and reset the game, the motor in the cabinet just spins endlessly without actually resetting. I have to manually operate the ZB1 and ZB2 switches to reset the game.

If I play a 1 or 2 player game, none of the above happens. The game works as it should.

If I add points to Player 3 and cause the problem (won't advance to Player 4), I must manually press the Z1 and Z2 switches to reset the game. They will never reset on their own after the fault situation is created. Therefore, I assume the Z1 and Z2 switches are working correctly, but something is stopping them in this particular situation? That could be a bad assumption - I don't know what I'm doing!

Thanks Rolf. I'm trying to decipher the schematic but having trouble understanding exactly where to attach the alligator clips.

Thanks Rolf, I'll give this a try this weekend

Hi Rolf and everyone else who took some time to respond. I don't know exactly what caused the problem but it now seems fixed. Following advice above, I did the following:

1. made sure Z1 and Z2 N/C switches were clean and actually closed when not pulling
2. traced the wires suggested by Rolf to ensure no bad solder joints or breaks
3. Cleaned jones plugs that the wires above were passing through

Along the way, I found an "F"switch/unit that was not properly engaged and was filthy. I cleaned that up and manually ensured that the unit arm was stepping through each number

I also found a weak solder joint on player 1 100's solenoid that I resoldered

As I said, not sure which of the above actually fixed the problem but your suggestions gave me direction to step through this methodically instead of being overwhelmed by all of the wires.

Well, guess I spoke too soon. Now I have a new problem. When I get to the 5th ball on player 1, the player 1 light turns off, and the chimes stop ringing for each point. On game over, player 1 and player 4 light up on a 1 player game, but the game ends properly.

I think maybe the player unit has some issues, it doesn't always advance smoothly. I've tried cleaning it up (rivets are all clean) but maybe it's sticky or something.

Back to troubleshooting. . .

I will try this, thanks

Last issue with this machine. If I can get it fixed, I will have gotten my first pinball back to 100%.

If I start a 4 player game, Player 1 gets a free ball. First ball plays and scores but the Ball 1 light is dark. After the ball drains, Ball 1 light comes on and the game starts and progresses normally. When I get to Player 4 Ball 5, Player 4 gets an extra ball before game over.

This leads me to believe that maybe I put the player unit back together wrong (i.e. aligned with the wrong starting rivet). Does this make sense?

The player unit was indeed off by a step. Thanks to everyone who helped - I wouldn't have been able to figure this stuff out without this great forum.