ASR 33 buzzing

It may be worth removing the belt from the motor : If an air deflector is fitted over the fan remove it by loosening thw 2 screws between the fan and the motor and removing the screw on top. Then unhook it from under the 2 screws and take it out. Undo the 2 screws on the clamps at each end of the motor (2 are the 2 screws refered to above) and lift off the clamps. Lift out the motor and free the belt from the sprocket. Hold the belt out of the way (with a bit of wire or something), put the motor back in place and fit the clamps to hold it. You can now get the motor running with no load, if there is a problem in the rest of the mechanism it can't stall the motor. The motor is fed via 2 pins of plug 4 at the back of the control unit. You can try disconnecting this to see if the control unit behaves. According to the diagrams I have, the motor is not powered with the switch in the 'Off' position. So you may have a problem with the switch or a shorted snubber network in parallel with it. There were various motors fitted to the Model 33 over the years. Some had a current-operated relay to disconnect the starter winding when the motor was up to speed (and drawing less current), If this is not closing at switch-on, the starter winding will not be powered, the motor can't run. The relay is a black plastic box on the mechanism chassis (IIRC to the left of the motor) with 3 wires going to it. -tony