Quoted from dmarston:
I agree. Rolf is heading in the right direction. Here is an embellishment:
Start a 2-player game.
Don't let the ball roll on the playfield, but manually actuate both a 10 and a 100 for player 1, ball 1. (Manually click the relay is one easy way.) Do NOT score any 1s!
Drop the ball in the outhole so that the game advances to player 2, ball 1.
Hit a 1-point switch and continue with the analysis suggested by Rolf.
Now you know the difference in behavior between the player 1 1-point reel and player 2's 1-point reel. If the problem is an end-of-stroke switch on a score reel, you'll probably see a difference.
If you can't complete the diagnosis, bring the game! Experts will be available.
When I start a 1 player game both reels reset to 0. When I start a 2 player game, player 1 score jumps to 50 points, actuating 10 points works fine, as does 100 points (by manually clicking the relay as well). After dropping the ball in the out hole it scores 20-30 points on player 1 score, then 30 or 20 points (always adding up to a total of 50 points) on player 2 score before doing anything. It's done this a few times when starting a 2 player game. After hitting a 1 point switch during player 2 game, it does the same thing and the 1 point relay locks up (along with the coil for the 0-9 stepper) then other times when I drop the ball in the outhole going from player 1 to player 2 the one point relay locks on, as does the coil for the 0-9 stepper unit.
Then following Rolf's analysis, when a game is started the 1 point score reels to reset to the 0 position. Then when scoring 1 point the relay locks on, as does the 0-9 unit, but the coil on the 1 point score drum does not pull. Following Rolf's theory, I start a game then hit a 1 point relay which locks on, but the 1 point score drum coil does not pull in. So I manually actuate the 1 point score drum and the 1 point relay and 0-1 stepper release the hold on. My guess is that the next step is to see why the 1 point score drum is not being energized to score and hit the end of stroke switch to release the 1 point relay and 0-9 stepper. Where do I begin to look?