Bally Knockout (Bally, 1975) (EM) ball count trouble

[pabilo21]

I am a new member and a newbie at working on EM pinball machines. I have a Bally Knockout with a double bonus scoring problem. While trying to fix this, I must have done something to affect the ball count unit. The ball count unit has 10 positions. It appears to advance one step each time the ball drains when in two player mode. From the schematic, I assume that it should advance two steps each time the ball drains in one player mode. It works normally in two player mode (the ball count unit advances one step for each ball drained). Each player gets a ball and then it correctly advances to the next ball each time when player 2 drains the ball. When there is only one player it gives the player two balls before advancing to the next ball. I am a bit confused by the Bally schematic and would appreciate any advice on where to start looking.
Thanks, pabilo21

 

[pinballdaveh]

both double bonus and ball count step up are controlled by the score motor. finding problems with the score motor inside the machine are difficult to find. to remove the bottom electric panel unplug machine,push line cord back into head as far as possible. unplug all playfield connectors and remove playfield and set aside. unplug all bottom board connectors,remove hold down screws or bolts. bottom board can now be lifted out and set crossways on machine. or if wanted to work on it on a workbench the line cord murt be completely removed from head. score motor,relays,and step units can now be manually checked for proper operation check for wires off,correct switch operations and wires touching other wires that should not be. reverse process for reassembly.

 

[pabilo21]

Thanks for the reply. I will be working on it this weekend.
pabilo21