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petenmi

Kitchenaid KHMS155LSS0 Loud Hum, No Heat

12 posts in this topic

Earlier this week the microwave began to make a loud noise when running the unit. There was no heat but everything else appeared to work (lights, turntable, controls and display, exhasut fan). Did some research and the mostly likely cause were either the magnetron, HV capacitor, or HV diode. Here are the results of my ohmeter tests on the 3 components:

1) magnetron - termimal-to-terminal short ckt; each terminal to magnetron case open ckt

2) HV capacitor- termimal-to-terminal momentary short ckt, than open ckt (same result with probes reversed); each terminal to capacitor case open ckt

3) Diode - Open ckt both direction (same result with probes reversed). Used both the ohmmmeter and diode check settings on my Fluke.

It appears that the diode may be bad but I read that if a diode fails open, there will only be no heat. If a diode fails closed, there will be a hum and no heat. Visually the diode itself looks good but the leads turn to a black color right before they enter the crimped terminals at each end. Could it still be a bad diode?

A few other questions:

1) Even though the magnetron tested OK, could there still be a problem with it? Any other tests to run on the magnetron?

2) Even though the cap tested OK, when I discharged the cap (terminal to terminal, and each terminal to the case) there was no arcing or popping noise.

Are there any known specific problems with this model?

Any other suggestions woul be appreciated.

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Why two topics for the same exact problem?

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Confirm that 120volts AC is reaching the transformer when the microwave is running to narrow the problem down to the high voltage components.

Check the diode this way:

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CEsQFjAC&url=http%3A%2F%2Ffixitnow.com%2Fwp%2F2010%2F08%2F26%2Fhow-to-test-the-high-voltage-rectifier-in-a-microwave-oven%2F&ei=4CZ3T4mOFIGTiQKcybCnDg&usg=AFQjCNHLf_5Damuqp_R39w85Ezk_Bm9ilQ

As for the magnetron, check this out... can't seem to post the link for "the Willie Method.

Search this site for "willie method" for some good stuff on magnetrons.

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The magnetron test is in my blog. Search the blog section of this site for Willie magnetron and you'll find it. I would but I'm on iPhone right now.

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That'll do it! Domo, Reg. BTW, could you delete peten's other identical topic that he started on this problem?

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:thumbsup:
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Yamabushi,

Thanks for the tip on how to check the diode with a 9V battery. Using your method,I get 9.1 volts when the cathode side of the diode is connected to the positive side of the battery and when the cathode side of the diode is connected to the negative terminal of the battery I get a negative 8.6 volt reading. Is this a bad diode? If so, does the failure mode of teh diode explain the symptoms?

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... I get 9.1 volts when the cathode side of the diode is connected to the positive side of the battery

... and when the cathode side of the diode is connected to the negative terminal of the battery I get a negative 8.6 volt reading.

... Is this a bad diode?

... If so, does the failure mode of teh diode explain the symptoms?

yes

http://www.repairclinic.com/referral.asp?R=154&N=1454993

 

Diode-W10163432-00709499.jpg

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Just replaced the diode, turned on the microwave and the same hum sound with no heat.

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I perfomed that Wille magnetron test - I removed the two wires going to the magnetron and ran the unit. The microwave ran and the humming nosie was gone. Bad magnetron?

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