4 year old sharp microwave that overnight decided it'd do everything but
heat.

All functions normal, except heat. There is 120V applied to the HV
transformer primary, secondary measures 150 ohm, filament on both
transformer and magnetron shows negligible ohms, diode tests good on back
voltage, HV cap appears OK, magnatron does get very hot after a couple of
ten second tests...... ?????

I've had several with bad micro switches, HV cap, etc., but this one does
everything but heat for no reason.....

TIA