Have you just noticed that your M.O. is a bit on the smelly, gunky side? Then give this simple and CHEAP technique a try! For MANY years, people have recognized that vinegar is ideal for removing unwanted odors.
Remove any microwave turnables, racks, etc. Put them in a sink with HOT, soapy water.
Use a CLEAN, damp wash cloth to remove any loose crumbs.
In a microwave-safe bowl, place a half and half mixture in to the center of the M.O. It should contain HOT water and simple- everyday vinegar. (In my case, I use 1 cup of the water and 1 cup vinegar.) Heat the water/vinegar until it is boiling rapidly.
Using potholders, pull the bowl out of the M.O. and pour it down the sink's drain. Use a clean, wash cloth wetted with hot water to begin wiping down the top, sides and bottom of the oven. Rinse the cloth whenever necessary. When this is nice and clean, wash the turntable and racks. Dry. Put them back into the microwave oven.
Now, you're ready to use it again!