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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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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

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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.

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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.
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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.

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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.

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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.

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Remember... always cover your food...


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