Microwave ovens What is the little rectangular cover inside the oven and usually to the right hand side do.Mine has started sparking when cooking.

save your sanity and get another one at a resale shop..that one may catch fire..

see the next steps and follow with common sense: God bless you
Microwave is arcing If you see arcing or sparking inside a microwave, turn unit off immediately. Arcing can be caused by having something metal in the oven cavity touching a side, an oven shelf is touching the side of the cavity, an oven shelf support has broken, microwave waveguide, or bad magnetron.
If your microwave has a shelf in it, and you do not use it, keep it out. If one of the shelf supports breaks or comes out, the microwave will arc where the support was. You will have to sand the spot down, paint with appliance paint and re-install support. If the shelf shifts on the support and touches the side it will arc.
Your magnetron waveguide will either come out of the top, or side of the oven cavity. Some will have a stirrer in it(mostly top waveguides) with a panel over, or just a cardboard type cover over it. Over time, the stirrer cover can become warped from the heat which will expose the stirrer's metal shaft which will then cause sparking. These covers and stirrers come in a kit and can be replaced from inside the oven cavity.
Your cover over a side waveguide is coated with a substance on it, and overtime this coating can come off from the heat and moisture in the microwave. These waveguide covers are very easy to replace from inside the oven cavity. Touch up any paint that may have chipped or come off because of the arcing.
If your waveguide cover and/or stirrer are all OK, then the spark is coming from your magnetron. The antenna on your magnetrom has overheated and burned, sending the microwaves out at the wrong angle. If you catch this microwave oven repair early enough, you can usually get by with just replacing the magnetron. If the arcing has caused servere damage inside the waveguide, you will need a new microwave. Waveguides are not replaceable and most you can barely see into them, let alone sand and re-paint. In this case of microwave oven repair, when you remove the magnetron, you will see the burned antenna, or your magnetron will fail the test bel

Presuming that you have iliminated the possibility of any metal objects that are not meant to be in the machine being in there (and this includes dishes and other items with silver or gold leaf on them, which WILL spark and burn!) then take a look inside the oven its self. You will find a waveguide cover. It is usually a strange flakey silvery plastic/card like material called Mica and is usually on the same side of the microwave wall as the control panel (So if the picture on this thread is accurate, I will guess the Mica cover is on the right hand wall inside as you look at the machine from the front) . Over time, the magnatron (the thing that creates the microwave energy) will often burn a hole through the mika, or cause a dark brown or black burn mark in it. If this cover is even slightly damaged then it may well cause sparking inside the machine. These covers are designed to be removed and you can buy replacements for them from electrical stores.

Hi,
Here is a tip that will help you to figure out what is wrong with yourMicrowave Oven....

Basic Microwave Oven TroubleshootingTips

heatman101

Hi, a mica cover is inside the oven cavity, usually on the right hand side or in the roof you will usually see a small cover that looks like it is made of cardboard. It is often held in by one or more screws. It is called the waveguide cover. It is usually made of a material called Mica. Its purpose is to cover the aperture through which the microwaves enter the oven cavity from where they are produced by the Magnetron behind the control panel. It stops moisture and food particles getting into the "workings" of the microwave.

That piece is called the waveguide cover. It's a mica sheet that goes over the hole in the side of the oven where the microwaves enter the cooking cavity. While the oven can work without it, you should replace it. It's meant to keep food particles and dirt from getting into the area of the microwave antenna, where it can possibly lead to damage.

I gather from researching the part that yours is a UK model oven. Here is a source for the replacement waveguide cover. If you're in some other part of the world, at least you'll know what you're looking for when you search for a more convenient source. You may be able to find a replacement locally, as the waveguide cover is a commonly-replaced item. Check with appliance parts houses or service shops in your area to see if one might be available.

I had the same problem with my microwave. There is a cover on the inside of the microwave called a "wave guide cover" which can cause the symptoms you described. It can be caused by grease or debris accumulating around or on the cover. Mine actually began to smoke and appeared burned in the top corner. It is very easy to remove and replace, and is pretty inexpensive and can probably be purchased online. They are model specific, so be sure to purchase the correct one for your unit.

usually sparks come from turning and cooking with nothing inside the microwave..if there is grease or something on the bottom the heat will generate a spark

The Magnetron has failed, causing the waveguide to become damaged. If the waveguide is damaged/burned the microwave can not be repaired and should be replaced.

The cover is probably the magenetron. That is where the microwaves come from. If the bread was moist, it might have left condensate in the unit which is causing the sparking. Unplug the unit, leave the door open over night. If you can remove that cover, do so. Be sure to carefully replace it before using the unit. Never turn on a microwave with nothing in it.