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Whirlpool Over the Range Microwave Hood Combination, model MH7140XFQ, Serial XC H 51 40739. Has a loud hum, then shuts down in about one second. Started doing this following an electrical storm that also took out the clothes dryer (was only a fuse). Suspect that the HV diode is bad, as it reads 28-ohms in both directions. Replaced that with a new one today, part #W10163432, still does the same thing. The new diode had infinity resistance in both directions (???). Did I get a bad one??? HV capacitor seems OK, does what a capacitor is supposed to do. Magnetron reads infinity resistance across the two leads. HV transformer has what seems to be normal readings: 0.6 ohms across the primary windings, 90 ohms across the yellow/ground terminals, about 0.1 ohms across the orange leads; no shorts between any transformer leads. The HV diode is still my suspicious part. 2nd question: Is this unit covered by the recall? Manufacture date is December, 1998.

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  • ricksteimel Oct 08, 2010

    Would it be worth the extra expense (about $10) to go get another diode, since the one I bought today doesn't act like a diode at all--I believe a properly working diode should show about zero ohms resistance in one direction, and infinity in the other. I can't return the one I bought today, as the purchase clearly shows that electronic components cannot be returned once they leave the store. The one I bought today says "made in China" (?). If I decide to buy another one, it will be from a different store. Also, any idea on how much a replacement magnetron might cost?

  • ricksteimel Oct 08, 2010

    Appreciate the fast response and "professional" assurance that I am on the right track to get the unit repaired and back in service.

  • ricksteimel Oct 10, 2010

    Hi again, Rylee, the microwave is fixed and working fine. I did some "fine tuning" on whether or not the diode that I bought was bad...found a website that described why some resistance readings might seem to be problemsome, re-tested both the shorted one and the replacement that I bought, found that the replacement was actually good, it was simply a problem with my trying to get accurate readings without using a surefire circuit to check its operation. Also, I did buy a new magnetron for about $70, it was on hand so I did not have to order it out. Installation took about an hour due to the intensity of getting into the heart of things and then having to come back out once the new one was installed, all is well now. Thanks again for your advice.


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Thanks for using FixYa. If it's a loud hum/buzz sound then 90% it's usually a bad magnetron and other times it's a bad high voltage diode. However, from what you have described it seems to be the magnetron. Please accept the solution if the issue is resolved or post a comment for further assistance.


Posted on Oct 08, 2010

  • Rylee Smith
    Rylee Smith Oct 08, 2010

    If you think that the part# that you bought is no good then yes it'll be worth a try to replace it with new one. Magnetron will cost you around $53 and you can buy it from this link. Please accept the solution if the issue is resolved or post a comment for further assistance.


  • Rylee Smith
    Rylee Smith Oct 10, 2010

    Good to hear that its fixed. Please let me know if you need further assistance.



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