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Microwave oven flashed and groaned, staining cover of waveguide

While thawing a single frankfurter between pyroceramic plates on the moving carousel, the oven groaned loudly and flashed at the waveguide cover. Afterwards the waveguide cover was discolored over an area the size of a quarter but intact. Internal enamel was intact also. No fuse reacted. After wiping the cover with a damp cloth, I heated a pint of water in a tough glass measuring cup and then a cup+ of water in a ceramic mug, successfully and without incident. Was one frankfurter too small and flat to absorb the rated 1100 watts? Does the oven probably need repair?

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I suspect the water content of the frankfurther was your issue. Operating a mwave at full capacity without adequate load to absorb energy would cause something like this to occur. Ultimately the energy had to go somewhere, it chose the weakest point to dissapate. You mention to glasses of water heated up fine? Then no worrie if theres no additional funny noises.

Suggest you lower the power level to around 25% to cook a furter. :o) Or put a mug of water in with it.

Posted on Dec 10, 2008

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Sparks inside a wolf mw24 inside in right wall cover plate

The right side wall cover plate is the "waveguide cover."

It protects the waveguide and the magnetron at the other end from moisture, grease, and food particles.

If these remain stuck to the waveguide cover, arcing can occur, which will damage and / or destroy the cover, the waveguide or even the magnetron or the oven chassis.

As with most problems, this should be addressed sooner rather than later or it will only get worse, and may become unrepairable.

The similar Sharp model R-530E-series service manuals are here and here. They will help with disassembly, but the external / cosmetic parts will not interchange.

The Wolf waveguide number is 801798 and Wolf part ordering information is here.

The oven cavity and waveguide must be clean and if any spot is scorched or chipped, it must be sanded smooth, cleaned and dried, then touched up with appliance paint, available from local big box stores, home centers, appliance parts stores, and hardware stores.

Leave the door open overnight to dry the paint. Then install the new waveguide cover.

If the chassis or waveguide have holes in them, the oven must be scrapped and replaced.

For more free DIY and other help & advice, feel free to contact me via my site.

Please include FULL model number*, FCC ID number*, + detailed symptom information. ( * on the tag in cooking cavity or around door frame or control frame or on back)

William E. Miller, AS-EET
Microwave Oven Control Panel Repair Nationwide
"Recycling by repairing since 1982"

Dec 05, 2016 | In Microwave Ovens

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Oven began to spark and smell. The waveguide cover broke apart & scorched side now won't heat. Clock/light work so does the turntable but groans. Is it fixable or done?

It is possible the magnetron may have been destroyed. Arcing in the waveguide would likely cause a significant increase of cathode to plate current through it; possibly melting it internally. You could also have failure of the high voltage rectifier; caused also by high current. If that's the only problem, then it's possibly repairable for a reasonable cost. You would have to repair and repainted the waveguide. Some waveguides have a vertical bar in them to aid in dispersion of the microwaves. If this is loose and shorting, then you'd have to replace the entire frame/cavity. Not very practical.

Mar 29, 2016 | Sharp R-1214 Microwave Oven

1 Answer

The unit started arching inside the front panel on the upper left corner.

Arcing Inside the Microwave - Martin Microwave Inc.
Microwave Glass Trays, : Arcing Inside the Microwave - Microwave Glass Trays 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
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.) ...


Dec 15, 2015 | Microwave Ovens

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I have a Sharp Carousel Microwave R-1460A. The disk on the ceiling, opposite the warming plate and about the same size, has severe burn marks (probably from food splatters). Any idea what that part is

see this indication and fix it. God bless you
  1. Waveguide coverSparking and arcing in a microwave can be caused by a damaged waveguide cover. Try removing the waveguide cover to see if the problem persists. Once removed, the waveguide cover can be inspected for burns, which will indicate if this is the issue. If the waveguide cover is burnt or will not stay in the proper spot it will need to be replaced.
  2. Cavity/Rack supportIf sparking or arcing in your microwave is near a rack support, any exposed metallic area can be covered with a microwave cavity support. It is also recommended to replace the rack supports in this situation to ensure the issue is resolved.
  3. Cavity paintIf sparking or arcing in the microwave is visible on the side walls, the paint covering the metallic areas could have worn off or chipped. This can possibly cause pitting in the side walls or ceiling. If this is the case, it can be repaired with microwave cavity pain

Nov 08, 2013 | Sharp R-1460 Microwave Oven

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Flashing and buzzing in microwave while operating.

This sounds like carbon build up reacting to RF energy. You need to find where the burn spot is and correct it. It's probably behind or on the waveguide cover usually on the right side of the oven cavity. It looks like a brownish-tan plate about 2-3 inches by 4-5 inches. It's actually made out of mica or plastic. If you can't find the source of this problem, it may be inside the waveguide in which case the unit is not really repairable.

Oct 11, 2013 | Sharp Carousel Microwave Ovens

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Thermador Microwave Oven Model MBBS Serial No FD 8402000337 Runs but no longer heats food. Deep growling sound Light flashes from behind 4.25 x 5.5 " metal plate on right vertical side of oven...

Oh dear, I hope the magnetron still works. That plate you describe is called the Waveguide Cover. This cover must be kept clean otherwise the food particles will carbonize and cause exactly what you have described.
Contact the manufacturers web site for a supplier in your area or look on ebay, depending on your location.
When it has been changed, I hope the magnetron/aerial is OK.

Dec 29, 2010 | Thermador MBBS Microwave Oven

1 Answer


Here's a link to the parts listing at

The list also includes helpful schematic diagrams that you can print for future troubleshooting.

if you need further assistance, please post back and let me know. I hope this helps you.

Nov 03, 2010 | Sharp R-120D Microwave Oven

1 Answer

It makes a groaning noise and does not heat up. There is a burnt area on the top, middle, right hand side.

You may have a shorted high voltage diode, but I would suspect that you also have a failed magnetron, and with the burns you mention, the waveguide of the oven is possibly damaged, which is unrepairable.

Details covering some previous models are in their bulletin here. Even if your model is not on the list, the same problem can occur.

That bulletin has a picture of a burned waveguide.

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

May 25, 2010 | Hotpoint REM25SJ Microwave Oven

1 Answer

Ceiling plate cover has small hole; otherwise works fine.

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

It is part # PCOVPA180WRP0 (copy & paste) and you can
order it from Encompass here or you can call them toll-free at 866-779-5835.

In some cases the part is held in place with a rivet. Other times it just slides out of the slot.

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

May 24, 2009 | Sharp R-1870 Convection/Microwave Oven

1 Answer

Buzzing noise and flashing

Some units have a silica plate covering the waveguide opening. If it get burn spots on it, it'll do that. Remove the plate and try the unit. If it's OK, go to your MW repair shop and order a new plate.

Remember... always cover your food...


Mar 10, 2008 | Emerson MW8102SS 1100 Watts Microwave Oven

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