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Why is my microwave not heating?

I have a GE microwave, model JVM6175SF1SS. Pretty standard builder grade model. Recently it just stopped heating. When I turn it on, the timer and light turn on, but that's it. No fan, no turntable, and no heating. I thought the magnetron might be busted, but would that affect the turntable and fan? I checked the door switches, they seem to be fine. What could be the issue with it? I am selling my house and would like to have one less thing to be broken.

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Mine might have started a little different, but similar.

On and off the past few months, the cooling fan for the internal components would stay on after the microwave had stopped and we opened the door. As soon as we closed the door, that same fan would turn off. Nothing to do with the hood fan.

Today, much different issue. The microwave has power. The clock/display works normal, the control panel seems to be fully responsive and the lights inside the unit work. When the door is closed, the light is off. When the door is open, the light comes on.

But when we put food in it and hit a time and start....The light comes on and nothing else happens. The turntable does not rotate. No fan.

We can program a time and hit start. The light will turn on. The timer will start counting down. No fan, no turntable. I'm afraid to leave it on for more than a few seconds so I have no idea if it is actually heating.

Is it the door switches? The Magnetron? The fuses? All of the above?

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Hi @enron_hubbard

You said that the timer turns on so I presume you mean the display is on. Can you alter any settings on the control panel using the buttons, you didn't say?

The light is working (you didn't mention the fan), the control panel display turns on and you have tested the door interlock switches, I suspect that there is a problem on the control board - GE part #WB27X11080 (supplier example only).

Here's an image of the wiring diagram for a GE JVM series microwave. It is not for your exact model but the wiring diagram and the image of the control board part I linked (which is for your model) seem very similar. By that I mean it has relays that have similar designations regarding their function etc.

To get the light, fans and the turntable to rotate and also the HV circuit ( magnetron circuit) to work relays on the control board have to be operated to connect power to them. These are operated depending on what signals the control panel has sent to the control board.

It could also a faulty contact in the start button on the control panel GE part #WB56X20404 not sending the signal to the control board which would operate the main relay to start the heating process.

IF there is a 16 wire ribbon cable between the control panel and the control board you can use an Ohmmeter (high resistance scale) to check for continuity between the pins as shown in the table in the image to see if the Start button is OK when operated. As I mentioned earlier this is not for your exact model but hopefully it will be similar and relevant.

if the control panel tests OK (check some more buttons) then its the control board.

Be safety aware when working in microwave ovens. Disconnect the power to the oven and then correctly discharge the HV capacitor as soon as it can be accessed, before performing any other work inside the unit

Block Image

(click on image)

Update (09/03/2022)

@enron_hubbard

Are you testing the interlocks with the door open and the wires still connected to the switches ?

If so you may get those resistance readings as you're measuring other components not the switches.

With the power disconnected and with the door shut and the wires disconnected from the switches, one should test short circuit i.e. 0.00 Ohms (primary interlock) and the other one should test OL or open circuit (monitor switch), when measured directly across the switch. With the door open it should be reversed. The primary interlock switch should now test open circuit and the monitor switch should test short circuit.

Here's the JVM series troubleshooting flowchart that may help.

Block Image

(click on image)

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@enron_hubbard

If the thermal fuses were the problem then the oven light would not turn on either as the power for the light is through the both of them but not through the primary interlock door switch.

My answer was predicated on you saying that the door interlock switches tested OK.

If you verify that they are working OK it's back to the control board.

Also if I misunderstood what you meant when you said that the "....timer turns on..." and that you meant that it starts to count down after the Start button has been pressed then the control panel would appear to be OK.

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Hi @reg_hartner13

It could be a problem with the door interlock switches not operating/releasing when they should.

They are both operated by the door latches.

The primary interlock switch is a N.O. (normally open) type and the monitor switch is a N.C. (normally closed) type. This is with the door open!

Check that both the switches are operating/releasing correctly with the door open and then shut.

The primary switch will close when the door is shut and be open when the door is open and the monitor switch is the reverse i.e. closed with the door open and open with the door shut.

If the primary switch doesn't close there's no power for the fan/turntable/HV circuit, if the monitor switch doesn't open the HV circuit won't work.

You can always test an oven if it is heating with no turntable etc, by placing a microwave safe cup filled with water in the oven and turn it on for a minute or so and then check if it has warmed up at all.

Be safety aware when working in a microwave oven. Disconnect the power and correctly discharge the HV capacitor as soon as it can be accessed before doing any further work. The HV capacitor can store 6000+V DC for months. This amount of voltage can seriously injure you.

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According to the above schematic, no fan, turntable or heating would be a primary interlock problem. That is one of the door switches.

It could be the switch, a worn trip mechanism, or a bad/burned spade lug on the switch. You must open it up to fix it. Then eyeball it to determine if the spade lugs on all the switches are OK. Then verify that the door is activating ALL the switches. Then verify the the switches are all working using an ohmmeter.

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This has happened with my microwave before. I'm not sure how I solved it, but I jiggled the thermal fuses and then it started working. I haven't checked the fuses yet, but I will do that and test the door switches again. I assume if the door switches were malfunctioning, it wouldn't even start?

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@enron_hubbard If that MONITOR switch does not open it will trip your breaker when you hit start.........end of story. Normally, there are 3 switches and the monitor switch is usually in the middle.

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Just checked all the door switches for continuity, they all pass. Next I checked the resistance on them. All 3 read in the ~600 ohm range. I'm kind of stumped as to what could be the issue. My next guess would be to check the circuit board but I don't see anything out of the ordinary on there. All caps and relays look fine, wires are in good condition. For good measure, I reseated all connections just to rub off any corrosion that may be on there. It still won't work.

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You must check the switches for operation. That means continuity/open when operated. Lacking that, you know nothing about them. Then you must verify that open/close door activates them. Or just verify operation with door.

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