Clean the interior of the oven chamber after use with a damp cloth and a drop of detergent if necessary. Built up food deposits can eventually carbonize resulting in sparks, arcs, heating, and damage to the mica waveguide cover and interior paint - as well as potentially more serious damage to the magnetron. If there is any chance of food deposits having made their way above the waveguide cover in the roof of the chamber, remove the waveguide cover and thoroughly clean inside the waveguide as well. Clean them up and use a vacuum cleaner to suck up loose dust. Keeping the ventilation free will minimize the chance of overheating.
Microwave ovens are probably the most hazardous of consumer appliances to service.
If you have the slightest doubts about your knowledge and abilities to deal with these hazards, replace the oven or have it professionally repaired. Inc. Pagewise makes no representations about the content published on this site. Pagewise hereby disclaims all warranties and conditions with regard to this information, and user agrees that all such use is at its own risk.