Microwave Oven - Magnetron End Cap Replacement

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jim hardy
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Question of you radar guys..

My 14 year old Panasonic Microwave Oven suffered a magnetron end cap failure
it commenced arcing and melted off a corner.

upload_2018-10-25_23-3-54.png


I noticed it's not sealed, brand new ones have a hole in the end ...
so i'm wondering just what does the endcap do ?
I find plenty of descriptions of cavity resonance and the path of whirling electrons

but only brief mention of the endcap ..

Is the endcap part of the tuned antenna assembly , with dimensions that are critical?
image courtesy http://www.radartutorial.eu/08.transmitters/Magnetron.en.html
upload_2018-10-25_23-11-51.png



or might i get away with soldering a copper pipe cap over the end ? With a hole of about same area as in the old endcap?

How hot does that part get ?
What is its purpose - just to short the end of the coaxial coupling ?

Thanks for a reality check,
link to instructive material appreciated.

old jim
 

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  • #2
OCR
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Question of you radar guys..
Well, I'm not a radar guy, but...
...or might i get away with soldering a copper pipe cap over the end ?
Take a look here... don't know if it will help or not. . :olduhh:

.
 
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jim hardy
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Thanks OCR

i found a "magnetrons for dummies" style Youtube that's sorta qualitative. Here's a snip i've annotated

extrapolating it to the point i'm on thin ice,
i surmise
magnetro_nwaveengths.jpg

since the endcap is about 1/7th wavelength

i'm going to guess its length isn't critical and try adding a ½ inch copper pipe cap sweat fitting over it.
That will keep me entertained while the replacement magnetron is en route.
It'll either work great or make a shower of sparks ,

Meantime i've learned about the mica 'window' that covers the waveguide at oven wall . I think that was my trouble - it had pizza spatter on it that got turned to charcoal , probably reflecting energy back into the waveguide. Replacement mica sheet is about five bucks on Ebay or Amazon.
upload_2018-10-26_17-28-17.png


Ahhh i love how it's the small things of the earth that confound the mighty ! So much to learn so little time ...

old jim
 

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  • #4
OCR
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it had pizza spatter on it that got turned to charcoal
My Wife said:
Told you so, see this!.
Jim Hardy said:
I think that was my trouble
Well...? ! . :oldeyes: .:oldgrumpy: .




Lol, you're welcome... . :oldsmile:
Thanks OCR
.
 
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jim hardy
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Take a look here... don't know if it will help or not. . :olduhh:
Thanks -
one of those videos at your link features a burnt mica window

upload_2018-10-27_9-19-54.png

mine looks very similar

new magnetron is due to arrive Monday.

Tell Mrs OCR i admire her troubleshooting skill !

old jim
 

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Microwaves are so inexpensive nowadays. What's the chance Jim that the new window and new magnetron cost as much as a new oven?
 
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jim hardy
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Microwaves are so inexpensive nowadays. What's the chance Jim that the new window and new magnetron cost as much as a new oven?
Part of it is "Beating the system". I've brought this one back to life so many times now i know my way around it .
And it's a pretty nice one with all stainless interior and exterior.

Magnetrons on Ebay cost from around 15 to 165 bucks , so i ordered a $15 one.
The mica window is about five bucks for enough material to make half a dozen of them.
If that doesn't fix it, well, Fair Anne gets to pick out a new one.

old jim
 
  • #8
jim hardy
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upload_2018-10-27_23-3-36.png


Thanks OCR

Well i just had to tinker some more.
The metal antenna cap resisted all my soldering tricks, even copper plating with sulfate.
So i decided to investigate by experiment whether my arcing was due to the charred mica waveguide window or to the melted corner on antenna cap .

I filed the jagged molten edges off the cap and reassembled the oven sans mica waveguide window.
To my considerable surprise it works just fine. No arcing and heats water as before the trouble.

I tried a piece of thin cardboard for a waveguide window, no go it's smoking and charring within twenty seconds.

So it looks like i'll have a spare magnetron Monday. Ordering some proper mica window material as soon as sign off here.

Thanks @OCR ,
Mrs. OCR's comment was pivotal.

now i know how important is that little translucent mica waveguide window. (Windowpane?)




.
 

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  • #9
dlgoff
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The metal antenna cap resisted all my soldering tricks, even copper plating with sulfate.
I recently had the same thing happen to mine. Mine was made out of aluminum. But instead of trying to repair it, I did what @anorlunda suggested; bought a new one.
 
  • #10
jim hardy
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Well, it's still going after almost a week
magnetron1.jpg


sorry for blurry image, my first attempt at taking a picture ever with Fair Anne's flip phone.

Magnetron2.jpg

It doesn't seem to mind the burnt end.

I think it's time to cut and fit the new waveguide window.

old jim
 

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