A "plastic" square has become

It sound like the antenna behind the plastic plate may be warped and touching the cavity. From my experience when they start shooting sparks it is time for a new microwave.

clean off the bad spot sand use tan/white enamel paint... it's o.k. no lead in usa paint just wait till dry before using

may have to get a membrane switch........could be starting to fail, become intermittent...i've had to replace these on occasion.

Sounds like the power relay has quit. Time for a new one.

The rusted areas will first have to be sanded smooth and cleaned and dried thoroughly.

Then you can apply some high-temperature appliance paint, available from places like Wal-Mart, Lowe's or Builder's Square.

Then be sure to promptly clean up any spills or steam after using the oven.

We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.

There are a couple of safety thermostats in the oven to shut down power if something overheats. One is on the magnetron tube (the microwave source), the other is on the cooking cavity. These sometimes go bad. There's also a power line fuse that may have failed, or become loose in its mounting clips. These can be tested with an ohmmeter; they should all measure very close to zero ohms if they're good.

Another possibility is that the control circuit board in the oven may have failed. I have worked on several Sharp ovens where the power transformer for the board has gone bad for no good reason. If the board goes bad the oven may appear to be dead as well.

Microwave servicing is best left to professionals. If you're thinking of keeping this one, take it to a service shop (or call for home service) and get an estimate. Then decide whether to repair or replace.

Hope this has helped a little. Thanks for using Fixya!

easy fis plastic panel covers it inside oven -unclip remove light and put cover back on- good luck and please rate me

Sharp calls that the turntable coupler when it's a separate part.

If it's part of the the part with three legs, that is called the turntable support.

You can order Sharp parts from Tritronics at http://www.wehaveparts.com

If yours is model R1610, we actually have that full service manual on our site at http://www.microwavedisplay.com/r1610_sm.pdf

We're happy to help and we appreciate your thoughtful rating of our answer.