Grinder hums but won't run. Capacitor seems good, and so do windings
I think the description you &quot;saw somewhere&quot; is something that you are not recalling correctly or is somehow missing some detail. The capacitor tests that you performed seem valid and seem to indicate that the capacitor is ok.
Since the motor hums and won't start manually, it seems likely that a winding is shorted or partially shorted.
Try manual starting with the capacitor and its winding disconnected - only the main winding connected.