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Repair and disassembly guides for GE Microwave ovens.

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Magnetron keeps running after cook cycle is done.

Intermittent problem: sometimes the magnetron will keep running after the cook cycle. The interior light, fan, and turntable all turn off at end of cook cycle, but magnetron will keep going and keep cooking food hotter and hotter until we open door -- magnetron stops. Close door again, the magnetron will keep going, but still light/fan/turntable stay off like they are supposed to.

Thought it might be the power relay (that feeds the magnetron) sticking...but I reason that, since the relay is NO (normally open), it would have to be fused/welded to stay shut. And if it was welded shut, it should be a permanent problem, not intermittent. Right?

Thought about door switches too, but I've tested every possible combination of the three door switches being activated/deactivated and can't get it to repeat. I often hear of bad/dirty door switches causing light/fan/turntable to keep going after cycle...and that is something I can reproduce just by a certain combination of door switches. Magnetron alone, via door switches I can't reproduce. So, not door switches as the problem?

Any thoughts?

Schematic:

Block Image

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Relays can stick intermittently. Once they start doing that it's only a matter of time until it becomes permanently stuck either open or closed. This is usually caused by buildup of something such as carbon from the small amount of arcing produced when it opens or closes. But it CAN stick intermittently. Next time it does it, give the relay a tap with the back of a screwdriver

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@brandon_k Well good to know -- sticking will soon become permanent...and then I'll have a house-fire on my hands. I'll be swapping out control boards then. Thanks!

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@itbebroke yes let's not burn anything down, shall we? If the relays sticks sometimes, time to replace it.

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Per jayeff's instructions, saying that the HV circuit (ie magnetron) only gets current if the Power Relay is activated, plus comments saying that relays can stick intermittently, I'll be assuming the Power Relay is on it's way out. Swapping out control boards to hopefully remedy this problem.

Thanks @jayeff !

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Hi,

What is the model number of the microwave?

Did you check the N.C. door switch is operating/releasing OK? Make sure that the door latch operating levers are correctly operating and releasing all the switches when the door is open/closed.

A lot of ovens have 3 door switches, 2 x N.O. and 1 x N.C.

When the door is shut the N.C switch opens which allows the HV circuit to function by removing a short circuit from around the HV transformer. When the door opens the switch closes again and short circuits the HV transformer preventing the HV circuit from powering the magntron. This is an inbuilt safety mechanism designed to prevent harmful microwave radiation (produced by the magnetron) from escaping out of the oven through the open door.

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Model number: JVM1440WD003

Yes, I saw from the schematics that the NC (monitor interlock) switch short circuits the HV transformer...and that switch still works fine b/c opening the door would still kill the magnetron even during malfunction. Also, per the schematics, even if that short-circuit switch was bad, and therefore stuck open, it looks like the HV transformer still can't get power unless the power relay is activated too, right?....so why would the power relay still be activated after the cook cycle has finished...AND yet still not also be powering the light/fan at the same time?

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@Sam Elsinger

Without seeing the schematic, (I can't find it online) I don't know. I would be guessing based on other microwaves I've worked on but if it is wired differently then that just misleads.

Is there more than one relay on the board?

if you have the schematic then post an image of it in your question. Here's how to do this on ifixit Adding images to an existing question

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Schematic posted. By the way, I got an email notification for your original post, but not for the comment you made 20 minutes ago...I just happened to be refreshing the page here. How do I get notified every time you comment too?

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@Sam Elsinger

You need to add an email address to your profile to get notifications.

You'll notice that there is an @jayeff under my avatar name whereas there is nothing under your USER ID avatar, just your name.

To get notifications click on your name to get to your account page > Edit > Profile tab and enter the details > Save.

So when you see a user on ifixit that has an @ symbol under their ID you can contact them in a question/comment/answer by adding their @ name.

Hopefully this makes some sense.

Looking at the schematic you posted (thanks for that) the power relay is used solely for the HV circuit and not for the fan lights etc. They have their own relays. The relays are operated by the control board so if the power relay appears to be always operated it may be sticking contacts on the relay or the control board has a problem and is keeping it operated.

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@jayeff You're right, fan/lights have their own relay (looked at the schematics too many times and was going off of memory when I posted that).

So, other than the Power Relay sticking (or control board improperly activating it) are you not seeing any other ways the Magnetron can be activated? No way the door switches would be doing that? (I don't see how the door switches alone could be doing it...but, as we saw, I'm no expert at schematics :)

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