Why is my microwave oven eating itself alive? - Page 1
Forum section: electronics / projects

author: calzap
author_rank: Frequent Contributor
timestamp: September 04, 2023, 06:55:03 pm
content: Started about 6 weeks ago. Occasionally, there will be sparks and bright lights from the screen where the waves enter the cooking chamber. Now there is just a big hole. Sometimes get sparks from the edge of the hole. See the pic. Other than that, it works fine. If there is any uncovered food in it when the fireworks occur, the food gets tossed. So, what’s happening? Screen losing or gaining grounding? Chemical changes in screen or its coating? Magnetron frequency shift? Nano-aliens? Or?Mike in California

author: CaptDon
author_rank: Super Contributor
timestamp: September 04, 2023, 08:22:50 pm
content: One and one reason only!!! It had organic dirt and/or moisture on it. It began to burn and carbonize and now it will always continue to burn. You can by these 'mica windows' at an appliance repair shop or online. You must clean up any soot left behind or that will arc and burn also!! The oven will run without it but that is NOT recommended!!!

author: Gyro
author_rank: Super Contributor
timestamp: September 04, 2023, 08:34:41 pm
content: If the arcing has got to the point where the Magetron anode antenna cap is damaged too, those are also easily replaceable and available online. Don't use it until fixed, it will just add to the repair hassle and danger of Magnetron damage.

author: amyk
author_rank: Super Contributor
timestamp: September 04, 2023, 09:11:44 pm
content: That's the waveguide window. It's normally transparent to microwaves but if foreign substances get on it, they'll start to burn and result in what you're seeing.

author: calzap
author_rank: Frequent Contributor
timestamp: September 05, 2023, 04:11:09 pm
content: Thanks for the replies. I'll replace the mica screen real soon. So, basically it was the coating that changed ... coating became food particles that burned. I wonder if a fluoroplastic screen wouldn't work better. I think fluorplastics are pretty transparent to microwaves (true?), and food splatters might not stick like they do to mica.Mike in California

author: coromonadalix
author_rank: Super Contributor
timestamp: September 05, 2023, 05:13:18 pm
content: oily surfaces / residues etc .....

author: Gyro
author_rank: Super Contributor
timestamp: September 05, 2023, 07:57:26 pm
content: Quote from: calzap on September 05, 2023, 04:11:09 pmYou want to stick with the proper stuff. Even a small loss in a low thermal conductivity film is going to cause problems when you've got 600W+ coming out of a small waveguide (as witnessed by the degree of damage to the proper very heat resistant material), you could well end up with a soft mess and flames. The window material is chosen specifically for its properties, even if it isn't the cheapest or most user friendly.

author: calzap
author_rank: Frequent Contributor
timestamp: September 05, 2023, 11:46:08 pm
content: Oh, I'll replace it with the original material and don't intend to do any experimenting. I'm just curious as to whether other substances might work better than mica.Mike in California

author: moffy
author_rank: Super Contributor
timestamp: September 06, 2023, 02:33:09 am
content: Quote from: calzap on September 05, 2023, 11:46:08 pmMica is a great material for this application: thermally conductive (reduced thermal stress), high dielectric breakdown and transparent to microwaves as well as not flammable, it's a silicate. It has been used for years as a thermal pad for power devices, its one disadvantage is its brittleness.

author: Zero999
author_rank: Super Contributor
timestamp: September 06, 2023, 09:52:06 am
content: Beware. Mica dust can damage the lungs if inhaled. Wear a decent quality dust mask, whilst removing it and put it in a sealed plastic bag, before putting it in the rubbish.

author: calzap
author_rank: Frequent Contributor
timestamp: September 15, 2023, 07:09:39 pm
content: Fixed! See pic. Was able to find a near fit for a different model. With a little trimming, fits fine. Thanks for the help.Mike

author: mzzj
author_rank: Super Contributor
timestamp: September 16, 2023, 07:08:35 am
content: Quote from: calzap on September 05, 2023, 04:11:09 pm99% Doctors recommend NOT Burning fluoroplastics aided with boatload of RF.

author: coppercone2
author_rank: Super Contributor
timestamp: September 16, 2023, 08:32:40 am
content: you should take a look under the hood to make sure the wave guide is not burned up or damaged. I have seen it sparking there before and the problem ran deeper

author: Gyro
author_rank: Super Contributor
timestamp: September 16, 2023, 01:09:37 pm
content: Quote from: calzap on September 15, 2023, 07:09:39 pmThanks for reporting back - too few do.