Microwave magnetron cover replacement

[Harry Bloomfield]

Our trusty combi microwave oven began sparking yesterday, or rather the panel between magnetron and oven cavity did. Some of the panel was carbonised on the oven cavity surface, which I managed to scrap off and put it successfully back into service.

Anyone know if these are generally replaceable please, or the material used? it seemed to be an opaque white material with mica in a kind of sandwich, with the panel on brief examination stuck over the magnetron with something similar to double sided tape.

I assume the purpose of the panel is to simply keep food splatter out of the magntron, yet allow RF through?

As luck would have it, I gave away on Freecycle last Friday, a basic MW oven, which I had stored in my garage for the past 18 months, as a spare whch had been donated to me.

[alan_m]

It will be a mica panel. Available on Ebay and can be cut to size with a stanley/craft knife. You have to support the underside of the mica panel on, say, a wooden cutting board whilst cutting to stop it de-laminating.

Under £3 incl postage for a microwave size sheet.

I've replaced the mica panel on a couple of microwaves in the past decade without future problems. As you say the usual failure mode is fat/grease getting on the panel and then over time carbonising. It can be more of a problem with a combination microwave oven where the conventional oven operation bakes on fat splatters

[Jeff Layman]

Have you actually made a hole in it scraping off the carbonised material? If not, just rubbing off the carbonised stuff with fine wet emery paper should remove it without damaging the mica.

[alan_m]

Once it starts arcing there is probably a hole.

[Harry Bloomfield]

Jeff Layman explained on 30/08/2017 :

No, there is no hole, I simply scraped the black off the face.

[Brian Gaff]

Well, assuming it was a radio transparent material, almost any plastic will do as long as its not tinted, which might mean its got particles of material that would heat up in it. The normal problem for Magnetrons is that condensation gets into the seal with the outside world and causes the problems through scorching. Not tried combination ovens though, Presumably the material here in one of these has to actually survive in some quite high temperature situations, so the window on a standard microwave might not be up to the job. Brian

[Jeff Layman]

Not necessarily.

I had a 10-years old microwave which started sparking. At the time I didn't know about carbon sparking and due to pressing circumstances had to replace it with a new one. A few months later I cleaned off the carbon and the old microwave was back to normal. It's been working perfectly for the past 13 years!

[tabbypurr]

Sort of. Plastic works, the trouble happens down the line when it arcs due to dirt buildup, it will catch fire, which mica doesn't.

Nothing sort-of works too. But again any splatter landing on the red hot magnetron will instantly combust.

since it runs red hot that seems unlikely.

as long as it's mica not plastic.

NT

[Harry Bloomfield]

Brian Gaff pretended :

I had using clear plastic in mind, I actually use the microwave to test RF proof materials, but then I thought plastic would simply melt if the oven were used in its radiant oven mode.

[Harry Bloomfield]

[e-mail] formulated on Wednesday :

Some MW's do actually use a plastic window, between the magnetron and the oven cavity, so I would doubt they get that hot - obviously I am not about to test it.

[alan_m]

What gets hot in a combination oven is the oven itself. The window has to survive temperatures of 250C. Even in a conventional micowave the window may/will get splattered with hot fat at some time even if the interior of the oven remains relatively cool.

[tabbypurr]

As I said the magnetrons run red hot.

NT

[bilou]

The only thing that runs red hot in a magnetron is its filament.

[tabbypurr]

bzzt. I had a fire damged nuke with no magnetron to cooking cavity cover.

NT