Microwave will not heat up. All else is working normally.

Either you have an electronic part called a "triac or SCR that fires the magnetron circuit that is bad on the circuit board, or the H.V. Diode is leaking in the same circuit,but this is near the H.V. capacitor and magnetron components and can't help in supplying high-voltage( -D.C.) to operate the magnetron circuit,it might be the H.V. capacitor, but normally they don't open, but if if they short circuit,the internal fuse will open up