First take out all the balls, 6 of them...then put the game in switch test and check the drain switch. The one that's in middle of the apron see if its behaving correctly. Then check the trough optos, drop one ball and see if all the optos are registering. Then ball 2 through 6..you should see all the trough switches registered. Lastly look in the shooter lane and make sure the switch is not stuck on....report back