When I called the customer service tech said they suspected that either the magnetron or the diode had failed. The GE Adventism is 11 years old and as it was apart I decided to replace both parts as well as the capacitor. I had ordered the parts before I took the microwave out of the built in cabinet (needed help) and after testing components it appeared the diode had failed, the magnetron and the capacitor appeared ok although much of the color had changed on the tip of the magnetron. A replacement for the Microwave is about $2000 and decided to install all the new parts. Working well and appreciated the customer service help.