OP

Quoted from gottliebgreg:

While I was troubleshooting a bonus count down issue on Solar City, I came across what appears to be a design error. After I had corrected various issues with the bonus count down, I noticed that there was a strange ‘stutter’ with the “ADD BONUS UNIT” coil that seemed to occur every 120 deg of motor rotation. Everything appeared to be working properly, so I dug a little deeper and studied the schematic and timing diagram; here is what I found: The ADD BONUS UNIT coil is controlled by the G (BONUS SCORE CONTROL) relay, K (DOUBLE BONUS) RELAY and several motor switches. Three of these motor switches are of the longer pulse style and one is an ‘impulse’ style (at location 4A). Typically, the longer pulse motor switches are used in series with the impulse style to provide a short pulse to drive a bell or knocker at the proper time during a motor rotation. What I noticed was the 4D switch was in parallel with the 4A switch when not in double bonus. This results in the ADD BONUS COIL being driven for 15 degrees of motor rotation at the beginning of every cycle instead of the usual >7.5 degrees. Moving the low side of the motor 4D switch from one side of the motor 4A switch to the other corrected this timing issue and eliminated the stutter.