Edgard T Los Lunas , NM March 12, 2017 Appliance: Model 721.67903600 Bulb burned Disconnected microwave, removed cover and replaced bulb. It took about 10 minutes or so. On this model the cover had 2 safety screws which require a torx bit with a hole in the center. Do-It-Yourself Rating: Repair Time Estimate: Less than 15 minutes