You microwave will run, but not heat?
How do I discharge the diode?
You don't discharge a diode.
You do want to discharge the high voltage capacitor.
This is how I discharge a high voltage capacitor.
First unplug the microwave.
Then take a large screw drive and short both terminals to the side of the cabinet and then to each other.
If you get us a model number we can try and find you a service manual.