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We've got a over-range microwave that's part of our 4 appliance set, so I'm not particularly interested in replacing it. It previously had an issue where it was buzzing very loud and not heating and I replaced the magentron and that fixed that issue.

Over the weekend it started behaving the same way (loud buzzing, no heat), so I ordered a new magnetron and replaced it last night. Now the loud buzzing is gone, but still no heat. I get the hum that I assume is related to the fan activity, but the slightly louder hum that goes along with heating is missing (I'm inferring a little here - what I hear all the time now is the sound that I get when I'm running it at less than full power and it's not in the heating cycle - I never hear the sound that I used to get when running at less than full power and it was heating).

Any clues on how I should troubleshoot, what other component might be bad, and whether or not the magnetron was bad in the first place?

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  • I'd suspect a safety switch, jarred out of position; jiggle the door...
    – Mazura
    Oct 15 '14 at 3:00
  • @Mazure not sure how that could be - wouldn't that stop it from operating at all? It does run, just without heat.
    – cori
    Oct 15 '14 at 6:31
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    I've had one where that was the case, not everything is protected by the safety chain. Says here it could be the thermal cutoffs or the transformer: doityourself.com/stry/repairmicrowave -
    – Mazura
    Oct 15 '14 at 7:19
  • Thermal fuses on microwaves are often one-shot. There was probably one located directly on the old magnetron. Did you replace it? Some manufacturers have also been known to hide the things in other places as well. Look for them.
    – Wayfaring Stranger
    Oct 15 '14 at 14:05
  • Good description of the problem. I have the same issue, but I do hear the slightly louder hum, but still no heat. (I assume the slightly louder hum you're talking about is what goes on and off periodically when the power setting is below 100%?)
    – Ken Zein
    Dec 30 '15 at 18:09
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"Don't do that"

Skull and Crossbones

I'm not saying that you should not repair your microwave, but as a general rule, I would not recommend it:

Careless troubleshooting of a microwave oven can result in death or worse. Experienced technicians have met their maker as a result of a momentary lapse of judgement while testing an oven with the cover removed. Microwave ovens are without a doubt, the most deadly type of consumer electronic equipment in wide spread use.

The power supplies for even the smallest microwave ovens operate at extremely lethal voltage and current levels. Do not attempt to troubleshoot, repair, or modify such equipment without understanding and following ALL of the relevant safety guidelines for high voltage and/or line connected electrical and electronic systems.

We will not be responsible for damage to equipment, your ego, county wide power outages, spontaneously generated mini (or larger) black holes, planetary disruptions, or personal injury or worse that may result from the use of this material. -- http://www.repairfaq.org/sam/micfaq.htm

"Try this instead"

For most people, replacing the unit or professional repair is a more reasonable risk.

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    @ben understood and in general agreed. I have an electrical background although I don't use it professionally and am comfortable with HV safety precautions. I just don't know much about microwaves....
    – cori
    Oct 14 '14 at 22:40
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    @Edwin If someone searching the internet for microwave repair lands on this page, "think long and hard before trying it" is an appropriate answer. albanyherald.com/news/2012/oct/16/… timesdispatch.com/news/man-dies-while-fixing-microwave/… dailymail.co.uk/news/article-2512024/…
    – user23752
    Oct 14 '14 at 22:56
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    @benrudgers Maybe appropriate on an Internet search, but it is not appropriate for this site per the faq: diy.stackexchange.com/help/how-to-answer: "The answer can be “don’t do that”, but it should also include “try this instead”. Any answer that gets the asker going in the right direction is helpful"
    – Edwin
    Oct 14 '14 at 23:14
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    @Edwin the help topic on how to answer is generic to all SE's. The DIY policy on dangerous questions is to provide an answer explaining why it's dangerous and should not be attempted
    – BMitch ♦
    Oct 15 '14 at 13:56
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    @BMitch At some point I would like to make an argument to change your stance on this. Answers like this are not helpful even from a safety standpoint, as they offer no useful specifics on the dangers. For me, all they do is discourage me from asking questions, because I think all I'm going to get is a bunch of people telling me I shouldn't do what I'm doing. We DIYers have enough people telling us "Don't do that".
    – Edwin
    Oct 15 '14 at 14:54

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