Question about Microwave Ovens

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Whirlpool Microwave I have a built in Whirlpool microwave (integrated with the oven) Model RM280PX8O3. When I turn it on cook I get a loud buzz/hum followed by a blown fuse. It takes a couple of seconds to blow the fuse. When I replaced the fuse I can put it on defrost, and the lights, turntable, everything works, until the unit cycles on , then I get the same buzz/hum. Seems to be only making noise when it cycles to cook. After the buzz/hum I can turn it off quickly without blowing the fuse. I have read a couple of posts- looks like high voltage capacitor, transformer, or magnetron. Any way to narrow it down? Easy job to replace- any direction is greatly appreciated!

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  • 3 more comments 
  • TheSavant Feb 02, 2008

    After further review, looks like the model is RM280PXBQ3

  • TheSavant Feb 03, 2008

    Thanks for the tips- I ran the following tests (and an ohm test of the HV components):



    --------------------------------------------------



    Discharge HV capacitor!


    2. Remove one end of the lead from the HV capacitor to the transformer.

    3. Start the oven.

    * Hum gone? If so, it is the HV circuitry, go to step 4.

    * If it still hums you probably have a faulty HV Transformer. (Not uncommon.)

    4. Discharge the HV capacitor again, reconnect wire and disconnect the 2 wires to the magnetron.

    5. Restart oven.

    * Hum Gone? If so, magnetron is shorted. Replace or get a new oven.

    * Hum still there? If so, go to step 6.

    6. You have either

    * Shorted HV capacitor,

    * Shorted HV Diode,

    * Shorted clamp diode across the HV Cap terminals (if one is present, about
    30% of microwave ovens use these). (The oven will run 100% without this
    protection for the HV capacitor but it should be replaced if possible.)

    * Some older Panasonic ovens have a HV reed switch and these can also short
    but these are rare now because of the age.



    After this test, and the ohm tests of the capacitor, diode, and HV transformer, It looks like I have a shorted capacitor or diode. I ordered them today, so hopefully this will fix the problem.

  • Anonymous Nov 08, 2008

    how to test magnetron

  • jellybean_mi Apr 08, 2009

    My Whirpool built in microwave hums too. But works fine otherwise. I did not notice any changes in cooking temps.



    I have no idea how to even start checking for problems. It is a microwave/oven combo. Do I pul it out completely?

  • Anonymous Mar 15, 2014

    loud hum, fuse blows

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  • Microwave Ovens Master
  • 8,820 Answers

I would suspect the high-voltage transformer in this case, but the capacitor may be failing.

The high voltage section uses and generates voltages that can be instantly lethal.

So I don't recommend that anyone work in this area unless he has either a lot of experience or at the minimum, a good understanding of the safety issues and procedures involved.

If you or a friend decide to work on it, we have *critical* safety, disassembly, and troubleshooting info at our site, and our link is at our listing here on FixYa: http://tinyurl.com/yzjozk

Also, there should also be a very helpful "mini-manual" hidden inside the unit behind the control panel. It's very helpful when troubleshooting.

You can usually find helpful exploded view diagrams and order parts by entering your full model number here: http://tinyurl.com/gv383

Here are some links you or a friend can use for test help, but read the safety warnings first:

http://www.gallawa.com/microtech/cap_test.html
http://www.gallawa.com/microtech/diode.html
http://www.gallawa.com/microtech/mag_test.html
http://www.gallawa.com/microtech/xformer.html

We're happy to help and we appreciate your thoughtful rating of our answer.

Posted on Feb 03, 2008

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