Our LSMG told us the circuit board in our 930 was to control the voltage for the transformer that powers the motor. Apparently it's not a standard 110-120 volt motor. I do not know the details of this or if he is right or not, as I have only seen pics in the shop manuals. But I do know the machine is a mechanical inside the head. No servos or other things but there are sensors for the stitch pattern levers and the needle up/down thing. So there are electronics inside.
Joe