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Repair and disassembly guides for Kenmore Microwaves.

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Microwave makes humming noise then blows main fuse when door is closed

The microwave in question is: Kenmore 363.62709200 'microwave/hood combo'

This problem originated a few months ago when the main (20A .025/1.25in) fuse blew. I replaced the fuse without issue and the unit worked fine for 2-3 months, but then had to replace the fuse again. This time the new fuse only lasted for about a week.

Now if I put a new fuse in it (while the door is latched), the internal fan cuts on and there is a humming noise (not sure if it's the transformer or magnetron or just the sound of the fan running, but the humming noise is coming from that general area) and after 30 seconds or so, the fuse blows again. If I open the door, however, the humming noise ceases, the fan cuts off, and the fuse does not blow (I currently have the interior light bulb removed and the door taped slightly ajar so I can use the range fan and light).

I checked the door switches, and the button on the secondary switch looked a bit worn so I replaced all the switches. Unfortunately, this did not remedy the problem and I'm not sure what to test next. I have tested the thermal fuses with the multimeter and they all show continuity.

Does this indicate there is a problem with the control board? Or maybe something within the high voltage circuit?

Please help

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I know this question is over a year old now, but I just wanted to comment to say I am experiencing an almost identical issue with a different Kenmore microwave (mine is model no. 790.80359310)

For several months now I have been regularly replacing the main fuse as it seems to go out every few weeks. There has been some speculation in my household that opening the door while the microwave is still zapping something is what causes the fuse to get blown. No idea if that's true, but something is causing it to happen.

This morning after a routine fuse replacement, I heard the buzzing humming sound when I plugged it back in. I then shut the door and immediately there was a flash and the new fuse was blown. I tried again, same story.

Sadly, I have no idea what to do next. But I thought I'd post here on the off chance that you found the secret solution. If not, hopefully someone else who is having this same issue will find this and feel less alone as a result. lol


Jack, you may have a dangerous appliance. I don't have access to a schematic of your unit, but in general, blowing fuses indicates a greater-than-normal current draw, which in turn indicates a possible short circuit in the line voltage or hi-voltage maggie circuits. If your unit blows them without the on-off switch being on, it indicates either a short before the switch, or the switch is stuck in the on position and the short is downstream. I'd quit trying to use it until I found out where that short is! Something is definitely wrong inside the case; you'll have to expose the innards to find out what, and do some troubleshooting with a meter. If you don't have some idea what you're doing, leave it alone, since the hi-voltage circuit can shock you even when it's turned off! I can guarantee a new microwave is far cheaper than an ambulance ride!


Thanks, Doug. I got tired of having to buy new fuses every couple weeks, so I did as you suggested and found a practically brand new one on OfferUp for a great price (from a guy who won it in a raffle at work and had nowhere to put it). So, house burning down evaded...for now!


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Squiggle, the door switch interrupts power to the hi-voltage/maggie units. 20A is a lot of current. Blowing this up only when the door is closed indicates a short circuit somewhere in the high power usage circuitry. Did you try using your ohmmeter to see if the resistance from the line voltage wire to ground is low when the power is disconnected? (Be careful when working around the HV circuitry; the capacitors - which could be the problem - can zap you even when power has been removed for some time.) Start disconnecting things until the resistance goes up appreciably. (Note: I don’t have one of these particular units, so this is just general advice, not specific to your unit.)

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