Arching when in use Intense arcing when the microwave is on. Wave-guard has been burnt. Arcing has caused some holes have appeared in the microwave 'gun'

Determine the precise location of the arcing. Perhaps the container with butter had metal in/on it. Does this occur with a cup of water?

It is likely at or near the mica cover over the microwave magnetron antenna. An accumulation of soap, grease, oil and food around or behind this shield will eventually cook down, and burn, as it converts to carbon. The element carbon is metallic and microwaves do not get along well with metals. Due to the close proximity of this shield to the magnetron antenna (usually less than 1/2 inch) the power is intense and arcing occurs. In a worst case scenario the metal band at the tip of the mag tube will melt, requiring the magnetron tube to be replaced.

Gently remove the mica shield, inspect, clean any debris, re-coat burnt or bare metal with appliance touch up paint, allow to dry and reinstall the shield, While the shield is off also look at the mag antenna to spot any burnt of melted issues. A bright light and a small mirror are useful for this task.

Mica is a delicate material and must be handled carefully - or replaced.

Hello Stephanie.
Get a new filter and try again.
Otherwise scrap the micro.
It the filter plate rusted through, or is it burnt?
The microwave's Magnetron-wave-guide is just behind this filter plate.
Looks like a small tube with a silvery cap with hole in center.
Very hazardous condition here.
The high energy from it is damped by the filter.
Is there food in the micro when arcing happens?
An empty micro will arc.

Arcing Inside the Microwave - Martin Microwave Inc.

microwaveglasstrays.com/shop/articles-arcing.html

Microwave Glass Trays, : Arcing Inside the Microwave - Microwave Glass Trays ...glass tray, microwave plate, glass trays, turntable, microwave oven, carousel, ...microwave energy, and will eventually it will start producing arcs and put out one heck... the damage is non-repairable and the unit should no longer be operated.

Notes on the Troubleshooting and Repair of Microwave Ovens

www.repairfaq.org/REPAIR/F_micfaq3.html

Microwave oven does not respond to START button. First ..... but with the leakage from the spot welded waveguide inside the unit. ... My clue in was a spark between the waveguide and the case, when I was messing with the Controller PCB.) ...

MICROWAVE OVEN ARCING ' MICROWAVE OVENS

Typically most arcing in a microwave is caused by food splatter. A microwave cannot tell the difference between what is on a plate or on the wall or ceiling. Every food particle in a microwave will continue to cook until it turns to carbon and will attract the microwave energy and focus it to that spot and the unit will arc. Thorough cleaning of the entire microwave cooking cavity and removal of any burn or soot mark will commonly stop the arcing. If your microwave has a painted cavity, you can even use some very fine sand paper to remove any burn mark. Always cover what you are warming and really keep the inside of the microwave clean. If your wave guide cover is made out of the Mica board, and If it has gotten wet from cleaning or from splatter, it must be replaced. You can either order a new one or order a sheet of the mica board and cut out a new one yourself. If the microwave is arcing in the waveguide, generally the unit will need to be replaced. One quick test to see if the unit will work is to remove the bad cover and place a small container of water in the unit, run the machine of a minute or so and see if it still arcs. If it does, the arcing is in the waveguide area, if not it may have just been a problem with the cover. You can run the unit without the waveguide cover in place, it is only there to prevent splatter from getting into the waveguide, so removing it to test the unit is ok. If the area inside the wave guide shows signs of soot and arcing. You can try to wipe that out with some alcohol or lacquer thinner and then try it again. Good Luck.

There is a shorted happening when the magnetron release energy. The problem of that is the waveguide already not in focus (already have a big hole on it) hence it scattered the microwave wave elsewhere inside the unit and also to its own metal casing. That cause's to arcing when operating.
Waveguide hole needed to be replace and it need some cleaning & painting of the affected metal (usually near around the magnetron waveguide). Once it's done the unit will not arcing again.
I do hope I answer your problem. Thanks for asking.

This is caused by either carbon arcing from carbonated food deposits or metal dish or bowl being used inside the machine causing a track. Even a recycled paper towel can cause it as the towels have metal traces in them.

Some magnetrons have holes in the antenna by design. If these are clean holes on opposite sides near the RF gasket then they belong there. If the holes are obviously burn damage but don't cause any improper operation, the oven is safe to use.

YOU SHOULD NOT RUN MICRO WITHOUT ANY THING IN IT / THIS WILL OVER LOAD THE MAG TUBE . AND SOME TIMES FRY IT .. The sparking and arcing is probably a bad wave guide . this is sometimes caused by food splater / it gets in the cracks and corners and then cooks till it truns to carbon which conduts the micro's and thus arching .. clean it good and touch up any burns in the metal and repl wave guide cover. mm hope this will help .. mm

Hi,

It looks like there's lightning (arcing) inside my microwave When you see arcing inside your microwave, it's because of food or liquid left in the cavity or on the wave-guide cover:

• If the wave guide has any burn spots, replace it and clean the unit well.
  
  
• If the cavity has any burn spots, spot-sand it smooth and touch it up with microwave interior paint.
  
  

Note… If there are any burn holes in the cavity, don't use the unit-seek help from a qualified appliance repair technician.

Thanks for contacting Fixya

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.