Tbh the head motors are crap and dont last long, the pcb rarely fails but a knackered motor will cause the 1 ohm wirewound resistor to go open circuit.
I think there is only a a bridge rectifier - an electrolytic cap, 4 discharge resistors and the 1 ohm resitor on the pcb - oh and some versions have the trip switch too.
Do you suspect yours is faulty ? or maybe you have a knackered head motor ? - what's the actual problem you have ? i ask as many other issues can cause no head operation.