For the tests I did, I disconnected the connector 'spades' from the carbon brushes. I think the motor might be at fault, see diagram. I suppose I'd be struggling to get a circuit diagram of the PCB. Perhaps it was to simplify the front panel back when it was designed, maybe late 90’s. I'm puzzled why the PCB has a big rotary timer thing plus what seems to be a microcontroller. I wonder why there would be 3 separate windings though what is different about the supply to each set? The controller looks a major effort to remove once it's out I can test the triac. Looks a pretty small triac (on an admittedly large heatsink) to drive such a motor. Then the triac controls the phase at which current flow starts in the windings I guess. The brush wires are brought out from inside the motor, perhaps the commutator is in series with the windings - so that the AC magnetic field on the rotor maintains a known relation with the rotor (and so logically it is a bit like a DC motor). How do I test the big AC motor? Is an inductance test better than a resistance test maybe: look for 3 inductances. I replaced the brushes and nothing happened.
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