Question about Panasonic NN-SN657SMicrowave Oven

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Arking through the heat-vapour barrier(MICA cover) The arking actually burned through the MICA. I replaced the MICA with lexan, but now the oven shuts off before the specified time and is barely heating water.

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  • 5417376 Sep 25, 2009

    Thanks "Fixer", you are right the fumes coming from the oven was auful when I thested to see if the lexan would work. By the way my oven is the Genius sensor NN-T695SF 1300 W. unit and I got a part number and a $20 price for the Mica-cover. As you rightly observed, there must be a cause of the burn-through. I may buy and replace the mica without achieving a fix. I recall that the arking started when I placed a cup with gold rim. Maybe that provoked the inetial burn-through giving the discharge an unhampered path.

    So the BIG question is: Will replacing the mica cure the low power and eratic truncation of the assigned time that I enter for a given task? Note, the lexan seems to have stop the arking.

  • 5417376 Sep 25, 2009

    So it seems that I will have to throw this out there to see if someone is particularly conversant with whether ithe mica is responsible for the power level of the oven. By the way I did not place mica in or on the window, just in place of the burned through mica.


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Don't use your microwave with Lexan in the window. When heated, Lexan gives off extremely toxic gasses. It can also catch fire. If you need to replace the mica, use the original product to replace it. There has to be a reason, that the mica burned through. If you are using a home style unit, it isn't made for institutional use. Home use microwaves will tolerate about 25% as much use as a industrial, or institutional microwave, in a 24 hour period. The amount of moisture that gets into the original window in a home unit is normally a lot lower. If you do a lot of cooking where there is a lot of water involved, you will also have moisture problems. A way to fight this, is to either wipe the moisture from the inside when you are done, or leave the door open, so the moisture can evaporate.

Posted on Sep 25, 2009

  • David Shaub Sep 25, 2009

    I totally destroyed my old microwave this way. I had a plate with a 1/4" gold stripe around it. I thought it was just paint. WRONG. I never saw so many pretty colors before. When you put the cup with the gold rim in, you actually vaporized gold into the insides of the oven. For safety's sake, buy the mica shield. When you have it apart, wipe everything with denatured alcohol. It cleans much better than rubbing alcohol. Liik for gold deposits and remove them. If you have a shelf in the unit, make sure the edges are as clean as new.

  • David Shaub Sep 25, 2009

    Mica will insulate at the rate of about 1000 volts per 1/16 inch. It ia also a fantastic heat shield. If moisture got into the original mica sheeting, it destroyed the mica. Since you put lexan into the same area and you smell it when you use the oven, I'd replace it with another piece of mica. Check the component that the mica is next to. It's probably a high discharge capacitor. Make sure it has no signs of damage.

    I originally thought you were talking about the shield in the door, the window. We've had it describad as almost anything you can imagine.


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