When the 5th ball goes into the outhole, do the score reels reset, the game goes to ball one, and it's ready to play a new game? Or do the score reels reset and the game over light / match light turns on?
You would need to look at the schematic to see what circuits and switches send power to the score reel solenoids. It could be an issue with a score motor switch in the same circuit that sends power to the score reel solenoids...