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KitchenAid Microwave - Loud hum/buzz,no heat - KHMS155LSS

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The latest in a line of New Year's Eve failures at OS's house (a few years back it was a busted heating pipe in the wall), our KitchenAid microwave (KHMS155LSS) failed on the last day of 2011. Very loud buzz/hum when energized - noise cycles on and off if set at less than 100% power - and no heat. Controls, lights, etc. all seem to work. Unfortunately, the replacement model is 3/4" taller and won't work with the custom backsplash above the stove so I am attempting my first microwave diagnosis and repair.

After pulling the beast off the wall and observing all safety precautions, I am about to order a new magnetron based on the symptoms and the following test results. Before I do, I wanted to poll the community to see if magnetron failure may have resulted from something else that I'm missing and to see if magnetron replacement is too tricky for a kohai (or whatever my newbie samurai status is).

Capacitor: fine (though I got no spark/pop when discharging with a screwdriver - is this a clue?)

HV Transformer: fine

Diode - fine. (Was glad I hadn't sold my 12V regulated dc supply at yard sale as the DMM wasn't strong enough and showed it as open before checking voltage while connected to dc supply.)

Magnetron - Short from filaments to chassis/ground

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Need appliance parts? Call 877-803-7957 now!

... Capacitor: fine (though I got no spark/pop when discharging with a screwdriver - is this a clue?)

... HV Transformer: fine

... Diode - fine. (Was glad I hadn't sold my 12V regulated dc supply at yard sale as the DMM wasn't strong enough

... Magnetron - Short from filaments to chassis/ground

1) Capacitor terminals not shorted ? . . . not shorted to it's case ?

2) Transformer:

Primary winding -- Less than 0.5 ohm (approx.)

Secondary winding -- 100 ohms (approximate)

Filament winding -- 0 ohms

windings to chassis -- Infinite

3) could have tried a 9v battery

4) Magnetron: wires disconnected

Filament terminals - less than 1 OHM

Filament to chassis - infinite

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Sorry, should have been more specific on my "fine" results

1) Capacitor - across terminals reads XXX ohms then climbs to infinity. Open (infinite) between either terminal and case of capacitor.

2) Transformer - Primary = ~5 ohms, Secondary = ~75 ohms, Filaments = ~2.5 ohms (are these close enough to zero?). Filaments to chassis = infinite.

3) 9V battery would have worked but now I can defend continued presence of 12V supply to wife on next garage inspection

4) Magnetron - terminals continous (less than 1 ohm), terminals to chassis continous (less than one ohm)

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... now I can defend continued presence of 12V supply to wife on next garage inspection

... Magnetron - terminals continous (less than 1 ohm), terminals to chassis continous (less than one ohm)

1) :whistling::thumbsup:

2) seems bad

http://www.repairclinic.com/referral.asp?R=154&N=1489083

 

Magnetron-W10245183-01088762.jpg

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Thanks for link. New magnetron is on its way. I will report back once installed and reassembled. What causes magnetron failure of this nature?

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... What causes magnetron failure of this nature?

could be age or over-heating,

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Magnetron replaced. Microwave reassembled. All knuckles either cut, scraped, or both. Heats water, no buzz, and has been hoisted back up onto the wall. If it breaks again, we're moving! Thank you all for guidance/confirmation.

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