1973 williams winner pinball machine

I recently bought a 1973 williams winner pinball machine it has been working great. Until one day when i went to start up the game: i flipped the power switch, pressed the start button and it went through the usual proccess of randomizing your horse for the race, but then it never stopped the randomizing. It just continued to flip through the horse numbers without ending.

I checked through the back box and under the playfield but couldnt find any obvious problems. I also went through a digital copy of the manual but that still didnt give me any help. I have a basic background in electronics and a good mechanical knowledge. Can someone please help me identify the problem

Thank you
Jackson