Microwave ovens

The job of the waveguide cover is to protect the waveguide (opening) and the magnetron from buildup of food particles and grease.

When the grease and food particles build up on and below the cover, they will carbonize and arc - and maybe even flame up!

The solution is to clean it and keep it clean - but if it's too dirty, it must be replaced.

Sometimes it's necessary to remove the cover to clean both sides of it, and to clean the edges of the opening it covers.

It is held in place with a small plastic rivet (or screw) and once that is removed, the cover will slide over a little then drop down.

Be VERY careful not to get cut on the potentially sharp edges of the opening, and do not spray anything into the opening.

Apply an alcohol-based cleaner (such as the purple kind) and /or gentle scouring powder to a cloth or paper towel and carefully wipe it out, then when it's dry, reinstall the cover and the rivet.

I suggest to my customers that they NEVER use any ammonia-based cleaner (like the blue stuff) on a microwave, since the amonia will crack and distort polycarbonate plastics.

Can't tell you much about your little rectangle, but sparks can result from left over food particles that got carbonized, and a good cleaning might get rid of it, unless you like looking at the sparks(I heard you shouldn't stare at a microwave while working though, washing machines are safer).

make sure you unplug it while cleaning or doing anything else, those micros are dangerous as hell.

Take care