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My 3 year old Whirlpool Over the Range Microwave was sometimes not detecting the door as closed (when it was) when I tried to running it. All it took was a couple of opens and closes and eventually it would register.

It's been like that for a several months and I never really did anything about it. However, the other day I got curious and thought it might be a sticky door latch, so as I kept the microwave door open I stuck a wooden pick in one of the door slots (top one) and I assume this activated the switch on the top only (heard it click in). I then realized my microwave now had no power at all (screen was completely off).

Any idea what could've happened and went wrong?

I am almost completely certain that the act of me sticking the pick in the top door latch is when the microwave went completely dead.

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    so you simulated door close when it was actually ope, yes that would kill it
    – Traveler
    Jan 3, 2023 at 1:09
  • Yeah, this is what I figured. But my question is what is wrong now?
    – Chris
    Jan 3, 2023 at 1:13
  • It shorted, so now try to find the fuse inside it.
    – Traveler
    Jan 3, 2023 at 1:14
  • Fundamentally, this comes down to engineering the safety so that a failed switch can't permit improper operation. Jan 4, 2023 at 4:30

2 Answers 2

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We are used to things like refrigerator or oven switches that turn a light on/off. In some cases they do a little more - e.g., my oven door switch also turns off the convection fan, so the heat of the oven doesn't all get lost when you open the door, but that is not a safety issue.

However, a microwave oven switch has to really provide safety. Nothing is 100%, but the risk to the user (and the lawsuits to the manufacturer...) of a microwave oven running with the door open is so great that a mechanism more complex than a simple plunger switch (as used with a refrigerator or oven) is used.

In particular the switch may include both a "normally open" and a "normally closed" component, even though you just see a plastic or metal piece jabbing into a hole. Which means when you close the door, the latch would make the "open" part "closed" (conduct current) and the "closed" part "open" (not conduct current). It is possible to design such a switch so that if the parts are not properly synchronized - e.g., both "closed" at the same time, which should never happen if the door switch is functioning properly, that it will make a deliberate short circuit through a fuse. Essentially a fail-safe so that a loose door switch - or a user with a toothpick - will cause a dead oven rather than an injury to the user.

Assuming this is the case, it should be possible to fix it, much as I did with a similar microwave oven that triggered thermal fuses due to a fire (a long story...). But those types of fixes generally require disassembling much of the oven - not a trivial task. If this is indeed the situation, you want to order replacement door switches (since you know they have problems from before the toothpick incident) as well as the fuse.

Generally speaking these repairs are simply not cost effective on a countertop microwave oven. The over the range microwave ovens tend to be more expensive, so the repair may be worthwhile.

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    Thank you for such a detailed explanation, really appreciate it! I think I am capable of fixing it myself, have done some research and know all the safety precautions to take. Do you think a blown fuse is now the reason it doesn't power on? If so, would it be worthwhile trying to replace the fuse and the switches as you suggested?
    – Chris
    Jan 3, 2023 at 1:22
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    @crip659 The really easy design is to base in on top/bottom single switches - super easy. I have heard (but not directly verified, because I am not in the habit of taking apart microwave oven door switches - I should do that (to the old oven) next time I get a new microwave oven) that each switch (top or bottom independently) can actually have microswitches that effectively make it so that within top (or bottom) it has to properly sequence between two switches and shorts out if it doesn't. Slightly more complex, but mass produced costs almost nothing and would provide a much higher level of Jan 3, 2023 at 1:44
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    Probably worth noting that sections of the inside of a microwave operate at extremely high voltages, and the caps can remained charged at that extremely high voltage for longer than you would expect. Days even. Be extremely careful if you are going to open up the microwave and dig around inside.
    – James T
    Jan 3, 2023 at 9:52
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    I would say that "poke it with a stick" indicates you may not be as "capable of fixing it" as you believe. Get it fixed professionally.
    – T.J.L.
    Jan 4, 2023 at 13:23
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    I am going to make the same comment as T.J.L. here: you are NOT as capable of fixing the microwave as you believe you are. Proof of this is in how you went about troubleshooting the original fault.... You have no apparent understanding of how a microwave actually works...
    – CGCampbell
    Jan 4, 2023 at 15:13
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You've already gotten the longer answer. Here's the slightly shorter and clearer one from the sci.electronics.repair FAQ:

Various door interlock switches prevent inadvertent generation of microwaves unless the door is closed completely. At least one of these will be directly in series with the transformer primary so that a short in the relay or triac cannot accidentally turn on the microwaves with the door open. The interlocks must be activated in the correct sequence when the door is closed or opened.

Interestingly, another interlock is set up to directly short the power line if it is activated in an incorrect sequence. The interlocks are designed so that if the door is correctly aligned, they will sequence correctly. Otherwise, a short will be put across the power line causing the fuse to blow forcing the oven to be serviced. At least that is the most likely rationale for putting a switch across the power line.

What does this mean for the next person finding this question? Simple: if you want to work the door switches back and forth for some reason, remove power from the microwave first!

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    thank you for saving the day
    – Traveler
    Jan 3, 2023 at 3:25

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