Could be a shorted transistor on your driver board or a fault with your motor control board. If you remove the plugs with the thicker wires from the bottom of your Driver board does the motor stop wen its turned on?
The spinning ball is Q30 on the driver board. J126 pin 7 is the drive signal. If you disconnect this, the spinning ball will stop, indicating a short in the driver transistor. You could measure the transistor Q30 with the game off and compare it with another transistor.
