You probably have a switch that's not making contact somewhere in the score reels. There's a video on it that Clay Harrell had on YouTube that I'd have you reference, but it seems he's pulled all his videos because of a recent piracy issue. Check out his pin repair site...section 3f discusses score motors, but again, I think your problem may also lie in a maladjusted score reel switch, so reference that section. Sniffing around this site for a while will take a lot of the mystery out of it for you: