On this era of Williams machines, the reset relay has a switch that closes to allow a pulse from a score motor cam to energize the subtract coil of the credit unit. So, the first thing I would check is the reset relay. Is it staying pulled in all the time? That would cause the motor to continue to run and it could also cause all of the credits to be taken off.
If the reset relay is stuck on, you will need to figure out why that is happening. This problem is often due to the runout switch on one of the score units not opening when that score unit has reset back to zero. However, there are other reasons this can happen.
- TimMe