Hi chaddy
have the playfield lifted and listen to the Score-Drums and watch the Score-Motor while the bonus is counted down --- the schematics says SCM-3 and SCM-6 for single bonus, SCM-3 and SCM-6 and SCM-4 and SCM-7 for double bonus. See here http://www.pinwiki.com/wiki/index.php?title=EM_Repair#Bally_Score_Motor the third picture, from left to right the cams: 1, 2, 3 etc.
Have the playfield lifted and listen to the Score-Drums and watch the Score-Motor while the bonus is counted down --- points made on the Score-Drums when Switchstack on cam 3 (SCM-3) is actuated ? OR when SCM-6 actuates ? Greetings Rolf