All microwaves have their lamps positioned outside the heating cavity so as not to interfere with the microwave process and to avoid arcing. Some lamps are accessable by removing a small cover on the rear of the unit. If you do not see any doors on the rear of the unit you will have to remove the metal cover.
To access your lamp you will need to remove the outer cabinet which requires removing all the screws around the back lip. With all the screws out, the cabinet should slip off the unit. It should pull up and to the front to get it off. In some cases the cabinet may stick due to food spills which have dried, holding the cover, even after all screws have been removed. Be careful but persistent and the cover will come off.
Once the outside cover is off the lamp should be visible. If not you may have to remove another dust cover to access it. At this point the lamp can be removed and replaced.
Replacement lamps should be available at Lowes Home Depot or http://www.repairclinic.com
.Be sure to replace the lamp with the exact same size/rating bulb and one which is designed to work in a microwave oven. These are specially designed lamps and therefore will cost more than a run of the mill lamp.
Installing a larger unit may cause overheating problems, melting or possibly even a fire. Reverse the procedure used to disassemble and your unit should be ready to go.
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