OK - clearer now..
Sounds like the plungers are not moving free in the score reels.
Prove this by playing a game without the ball and testing the movement and the advance of the reels.
Take the glass off, start a game and try this ;
Hit a 10 point switch - check to see movement from 10 - 90. Does it advance the 100 reel smoothly ?
Hit a 100 point switch - check to see movement from 100 - 900. Does it advance the 1000 reel smoothly ?
Hit a 1000 point switch - check to see movement from 1000 - 9000. Does it advance the 10000 reel smoothly ?
We need to see if the game has issues scoring as well as resetting.
