Burnt hole in metal plate inside microwave oven

Hi,
There are 2 things that cause the massive sparking:
1. you placed inside the microwave oven a metal plate or one with silvery or golden drawings;
2. the mica sheet that covers the magnetron window is compromised (has holes, it is cracked) or it is covered with burnt (carbonised) food.
You have to carefully inspect the mica sheet and wash or replace it, if necessary. Hope that helps.
Regards,
Dan

Make sure no metal item (forks-spoons or oven rack) is touching the outer wall of the microwave. That will cause sparks. If all that is OK then there is usually a metal fan type blade in the microwave top called a stirrer blade that may be out of place and rubbing the cavity causing sparks. Try to pin point the spark area so you know where to look for the problem. Sparks usually mean metal is touching metal somewhere.

Microwave ovens do not work well with exposed metal. IF you place uncoated metal in the oven, sparks will occur.
IF the interior of the oven has the metal exposed, it will cause sparking to occur.

There must be NO exposed metal inside a Microwave oven!

I had the same problem several years ago. I took it out and just left a hole. No problems yet.

It is very possible it may have burnt wire or burnt capacitor. Remove unit, remove top cover and look inside to see if you see any burn marks or burnt wires. Also check fuse to see if it is good or not.

you need to replace the cavity cover "the cardboard like",the antenna bearing set "the gun barrel like" and the gear motor.If the "gun barrel like" is stuck up because the gear motor is not rotating excessive heat will occur inside the microwave thus burning the cavity cover.

If it is burning and arcing at the antenna, it is probably arcing in the wave guide area. Probably will have to replace unit. I have had some success by removing the antenna, sanding and repainting the burnt areas of the cavity and sanding off any burnt marks on the antenna. Need to look at top of mag to see if also arcing there too.

This is the waveguide cover / stirrer cover.

Quite often this is due to grease or food particles stuck to the inside of the oven or stuck on or behind the waveguide cover.

It can be fragile, and the metal edges of the oven behind it can be sharp, so be careful!

The cover and the metal behind it should be cleaned with a mild, non-ammonia cleaner.

If the cavity metal of the oven is chipped or charred, it will have to be sanded smooth and clean and dried thoroughly.

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

If your waveguide cover is burned, it will need to be replaced. It provides important protection for the magnetron.

Please reply back with your brand and model number so we can help you in obtaining parts.

Otherwise, you can usually find helpful exploded view diagrams and order parts by entering your full model number here.

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

The magnetron has failed and has damaged the waveguide. This type of failure is generally unrepairable. First look in your owners manual for specific warranties, then contact Whirlpool and explain to them what has happened.

If you need further assistance, let me know
Regards,
reg501