Anna Marie A Lake Charles , LA February 26, 2015 Appliance: Model 721.80039700 It was not heating I replaced the magnetron. Being a past service technician, I had the experience and basically the ear to know that the magnetron was not working. Now, it works like the day it was purchased. 24 People found this story helpful Do-It-Yourself Rating: Repair Time Estimate: 15-30 minutes