Question about Whirlpool MH7155XM Microwave Oven

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Whirlpool MH7140XFQ Microwave just suddenly stopped heating. All other bells and whistles seem to work. Trying to troubleshoot and need schmatic. Trying to diagnose without dropping unit. Have had no trouble since safety recall. Any input as to most likely trouble? Any help appreciated! Thanks!

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  • mspauld Oct 21, 2008

    Thanks for the quick reply! To answer your main questions, nothing smells burnt, everything sounds normal while trying to operate, I just get no heat. I just pulled the unit tonite and began to troubleshoot, so far HV diode fails! Have not yet finished checking out transformer secondary, filament, magnetron, or capacitor. Am hoping diode is all that is wrong. Any advice on what to use to bleed capacitor to finish troubleshooting? Again, Thanks!

  • mspauld Oct 21, 2008

    p.s. - diode tests open

  • mspauld Oct 22, 2008

    Still not working even after replacing diode. Everything else checks out according to tech sheet from inside unit. Seems to be getting 120v to transformer primary, just no heat. By the way, I have never been able to get either diode (new or old) to show any continutiy in the forward direction. I have tried 3 different DMMs with same results. Could I have gotten a bad diode from the parts house or is this just a Fluke? (pun seriously intended). I feel that I am missing something basic. Help with how to check high voltage &/or magnetron side would be appreciated. I suspect that my capacitor is never seeing any charge. Thanks!

  • mspauld Nov 11, 2008

    Reply primarily to B Low:

    Short answer: no I haven't fixed old unit. The details: Got as far as measuring 120v ac across transformer primary while bench testing unit. No way that I know of to verify high voltage/magnetron side without killing myself. All of the troubleshooting measurements given on the unit's spec sheet seem to check out ok on the unit. I give! Went down to the local BestBuy store and purchased a new Whirlpool MH2175XS for around $260, old unit boxed in my garage in case I get bored or if MacGyver happens to come by some time. This is probably not the help your were looking for, but unless your more comfortable working with high voltage circuit than I am or your willing to pay a professional, maybe you gotta do what I did and put a bullet in it's head. Sorry & best of luck!

    ps- If your ever seem to find your trouble, please let me know!




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Did you get the unit working? I am having a problem with my same model microwave...

Posted on Nov 11, 2008


Sounds like it is the high voltage diode then. A fairly inexpensive part I think

Posted on Oct 21, 2008

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Does it make any noise, like buzzing ? Is there a burnt smell? If so it might be a shorted diode or perhaps the magnetron.

Posted on Oct 21, 2008

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