Towards the end of its startup sequence, Dimension will step up the ball count unit either three, five, or eight times—depending on the “minimum number of balls” setting in the lightbox. The stepping comes from pulses generated by score motor 1A. This is the lower cam with the little metal spikes that operate switches five times per 1/3 turn of the motor. Every time the ball count unit gets a pulse, its solenoid pulls the drive arm away and the drive pawl slides down one notch. The ball count unit, however, has not yet moved. When the pulse ends, the return spring pulls back the drive arm and its pawl, pushing the cam and advancing the ball count unit one position. The spring performs the work after the pulse has ended. This is known as an “indirect drive” system.

Every time the ball count unit’s drive arm is pulled down by a pulse, an end-of-stroke (EOS) switch on the back of the ball count unit gets closed. On pulse 3, 5, or 8, this switch sends line voltage to the sequence bank reset coil, which ends the startup sequence and the ball count unit stops adding any more balls. When exactly this happens is determined by the wiper board on the ball count unit: it has a set of rivets along the bottom that complete the circuit from the EOS switch to the sequence bank reset solenoid. Rivets 2, 4, and 7 are tied to the game’s “minimum number of balls” setting.

That said, here are some thing you should check: (1) the wiper board rivets or fingers might be worn out, (2) the wiper board might be misaligned, (3) the return spring on the drive arm might be too strong, (4) the ball count unit might be gummed up with old grease.

Good luck!