ok got it, the problem can only be one of two things, 1 the high voltage transformer
or 2 the magnetron and stirrer kit,
these are both on the high voltage end of the microwave and is very dangerous to work on, heres the warning,
Consumer Product Safety Commission
Electrocution Hazard with Do-It-Yourself Repairs of Microwave Ovens
CPSC Document #5061
The U. S. Consumer Product Safety Commission (CPSC) warns against do-it-yourself repairs of microwave ovens. Each year, on average, four people die from electrocution trying to repair their microwave ovens. Microwave ovens use high voltage which makes it particularly hazardous for consumers to remove the cover and touch electrical parts. The possibility for electrical shock from a microwave oven still exists even after the oven is disconnected from the power source. Should certain internal devices fail, even unplugged ovens can cause serious injury.
The Commission strongly recommends that consumers have professionals repair microwave ovens because electrical appliances can be hazardous if consumers expose live electrical parts.
Removing the cover of your microwave oven and touching an electrical part can kill you.
Have a professional repair your microwave oven
they show the magnetron still available but say the transformer has been discontinued, it may still be available with some research, I recommend having a tech work on this however, or replace the microwave, the parts are very expensive. thanks Bryan