JVM3160RF2SS GE OTR Microwave doesn't turn on - Thermal Shutoff and Internal fuse - both are blown -

[neozyklon]

Model Number

JVM3160RF2SS

Brand

GE

Age

1-5 years

Bought this GE microwave - JVM3160RF2SS slightly more than an year ago from Sears. Installed it myself. Now yesterday I see that it doesn't power on. I opened the microwave to see that the internal 20 A fuse is blow. I was about to replace the fuse and turn it on..Decided to do a bit of investigation. The door switches both are fine. But one of the thermal shutoff fuses are also blown. (70 V one) on the right. I will try to buy this part and replace both the fuse and thermal shutoff..I am trying to understand can thermal shutoff blowing cause the internal fuse to blow? Sometimes my gas stove underneath heats up the microwave when cooking at max flame. Could this have led to the thermal shutoff? I am trying to find some clues.

Should I check if the fan motor is an issue?

Any expert advice is welcome.

-Shari

 

[Jake]

Sometimes my gas stove underneath heats up the microwave when cooking at max flame. Could this have led to the thermal shutoff? I am trying to find some clues.

That's a very good question, it would seem logical, but I will ask Rick to see what he thinks.

Jake

 

[neozyklon]

Does the thermal shut-off blowing cause the internal 20 A fuse to blow ? It did happen in my case.

 

[rickgburton]

...can thermal shutoff blowing cause the internal fuse to blow?

It can. The difference between a TCO (Thermal Cut Out) and a thermostat is, the thermostat will reset.The one on the right is a thermostat. There's a bi-metal disc inside the thermostat that warps/bends when it gets hot. That opens the contact. When it cools it warps back and closes the contact. The bi-metal disc sits very close to the business end of the thermostat. When it fails the bi-metal disk splits in half and can touch the metal part of the thermostat. That's a direct short to ground and blows the 20 amp fuse. It's not common but it does happen. Remove power. Use your meter on the power cord to check for a direct short to ground The smaller terminal on the plug is L1 or "hot" side.



Thermostat WB27X11213


Forgot to add: Make sure the door is closed when checking for a short or the monitor switch will short L1 to Neutral.

 

[neozyklon]

Thanks Rick..Thats the exact part I have ordered - the thermostat . I did the continuity test on the 2 metal arms of this one and meter says it is open. I am guessing that indicates the thermostat has gone bad. Am I right?

 

[rickgburton]

You're right!

 

[neozyklon]

I bought a thermostat KSD201 /70 from LUNA part and I tested for continuity. It failed. I tried to install it anyways suspecting if I wasn't doing the continuity test correctly. It turned the microwave on/power/display all ON. But as soon as I tried to use to warm a glass of water, it blew the fuse (20 A ) again. I ordered for another KDS201/70. It also failed continuity test..Am I doing something wrong? Is this thermostat supposed to be open ? I checked the other thermostat in the microwave KSD201/120-0. It passes the continuity test..Is this the case of a bad part being mailed out to me twice? Please advice. I am losing my mind and it takes 2-3 weeks for them to ship any part..

 

[neozyklon]

What is the difference between KSD201/70 and KSD201/120 . Is one supposed to be open and one always closed at room temp? If thats the case, I am probably looking at the wrong part for troubleshooting my broken microwave..

 

[rickgburton]

It could be a normally open thermostat that closes when it gets hot to turn the fan motor on. Check the monitor door switch. The monitor switch, also called the dead man switch, is designed to keep the microwave from working if the door is open by shorting L1 and neutral together which blows the 20 amp fuse.

 

[leinoffs]

Hello,
I'm sorry if it is "bad form" to jump into this year-old forum with my similar issue (I am new to the forum),
but I have almost the identical model (GE JVM3160RF3SS) and my 20A fuse has blown twice.
I am helping a friend with this microwave oven/hood.
She told me the oven went "dead" when she opened the door while the oven was on.
I told her that I didn't think doing so was a major mistake because there are fail safe switches to shut down the microwaves when the door opens.
(...but I might be wrong about how serious a mistake she made.)

I took the unit apart enough to find that the 20A glass fuse (upper right circuit board) was blown.
I found a replacement at The Home Depot and put it in; reassembled the unit.
It powered up when I plugged it in and I reset the clock.
I then put a cup of cold water in and turned the oven on.
It took about two or three seconds before the unit went dead again.
I'd bet a lot that the 20A fuse is blown again.
I don't know what my next move is, but I suspect it will be to send her to the store for a new unit.
My friend has very limited resources, and I have nearly unlimited time and patience.
I'd hate to have her trash the unit if it could be fixed cheaply, but I'm not sure what the next step in troubleshooting would be.
Or, it it is most likely a failure of a major (expensive) part (e.g. magnetron tube, transformer, capacitor diode) and I'd just be wasting time trying to track down the real problem.
As they say, any expert advice would be greatly welcomed.
Chartman

 

[rickgburton]

It might just be a bad microswitch or or an adjustment on the bracket. Opening the door without pausing it first won't hurt the machine but it puts a lot of wear on the monitor switch. The monitor switch (also called a deadman switch) is a safety switch to keep the microwave from running if the door is open. L1 and Neutral are shorted together whenever the door is open but there's no power there until you push start. When the door is closed the switch is open. When the door is open, the primary microswitch kills the power a fraction of a second before the monitor microswitch closes. If a switch goes bad or if the bracket is out of adjustment, the monitor switch can closes while there's still power to the switch and then the fuse blows.


You'll need a DMM that can measure Volts and Ohms. Unplug the machine and remove the upper grill above the door and control panel. Remove the screw on top of the control panel. Lift the control panel and lean it forward. From there you can access the door switches. I will make you a diagram. Check all four microswitches but you might as well start with the monitor switch. When checking a switch for continuity, always remove at least one wire from the switch. Check the switches by opening and closing the door. A microswitch can be Normally Open (NO) or Normally Closed (NC). Each switch has a common terminal and the normal condition of the switch is when the button is out or if you were holding in the palm of your hand looking at it, that's the normal condition.

 

[leinoffs]

Thanks for the direction

Thanks for some great information!
I have had the control panel off already, so i think it will be easiest to get at those switches with the panel removed again.
I guess there must be some reason for four door switches, but hopefully with your diagram in hand I will be able to identify the monitor switch and make sure it is open with the door in the closed position.
I will also check the other switches.
I'm not sure right now (without looking at them) if I will be able to tell if each switch is supposed to be on or off in the "door closed position",
but at the very least I should be able to tell if they change from open to closed or closed to open when I operate the door.
I may not get back to make these tests for a day or two.
If I find that the monitor switch is always closed, I'll just order a replacement.
Same with any other switch that does not perform properly.
If they all test good I will report back here and hope you will give me some more insight.
Thanks, again!
Chartman

 

[rickgburton]

ok sounds good

 

[leinoffs]

Today's Adventure

ok sounds good

Hi Rick,
I went back today and opened up the unit as before; removing the control panel for better access to the door switches.
I found only three switches; top, lower middle and bottom.
I removed the connections to the top switch and checked the terminals with an ohmmeter.
I don't remember exactly which way it went, but clearly the switch was closed one way (door closed, I think) and open the other way.

Next, I removed the connections from the middle switch, which I took to be the "monitor switch".
The switch read closed with the door open and closed with the door closed. It looked like I was on to something.

The bottom switch tested good (i.e. different with the door open than with the door closed).

I also noted that the middle switch was especially floppy in its opening in the long switch bracket; more so than the other switches were.
I thought something might be broken to cause this, but I have come to change my mind.

The wires connect to the switches through (what I will call) a plastic connector.
The plastic connectors are fused together so that both switch connections must be made or separated at the same time.
Also, these connectors fit tightly in the switch bracket so that when they are connected, the switch is pretty much locked into position,
unlike its "floppy state" with the connector off.

I removed the switch bracket and released (what I assume to be) the monitor switch, which looked to be in good shape.
I "bench tested" the switch and it tested good (Normally on with the button out; off when I pressed the button in)
I reassembled the switches in the bracket and mounted it to the chassis again.
I wanted to test that switch again (door open vs door closed) but this time with the plastic connectors on it, but I am reluctant to cut a wire.
I was not able to release the wires from the connector, which I have often done with a tiny flat screw driver.
Ultimately, I jammed a piece of thin wire into the back of each connector terminal so that I could monitor the resistance with the connectors on the switch,
even though the wires were still connected to other parts of the unit.
Under these conditions I would not expect to see the resistance change from about zero to infinity,
but I did see a clear change (increase) in the resistance reading when the door was closed.
I think I have convinced myself that the monitor switch is working properly.
I did not think it prudent at this point to invest another fuse to see if the unit had somehow repaired itself.

While the unit was open, I noticed two round components at the bottom of the opening, which I took to be thermal switches (possibly?)
They each had two terminals, so I figured I would test them, in case it might provide some useful information.
The one on the left tested "closed" and the one on the right tested "open" (for what it is worth).

So, my friend has found that Best Buy has what appears to be the same model microwave oven on sale for about $200.
I am assuming that the wall bracket already in place is the same, which would make the mounting of the new unit pretty easy.
Do you think we're getting close to that option?
Chartman

 

[rickgburton]

The switch read closed with the door open and closed ...... was especially floppy in its opening in the long switch bracket;

When the door is open, the primary microswitch kills the power a fraction of a second before the monitor microswitch closes.

That little amount of play is necessary. That's as far as you need to go. The microswitch is obviously bad and needs to be replaced. It's easy to overthink microwave repairs so I always start with the obvious. The two thermostats on the bottom are: High limit thermostat is NC and opens at a set temperature and kills power to the cooking function. The other is a NO thermostat that closes at a set temperature and supplies power to the fan motor. Here's the switch you need:

WB24X10205 Switch Micro Monitor

 

[leinoffs]

Hmmm. That's not the response I expected.

I have rarely been accused of "over thinking" anything! ;->
I thought my follow-up analysis made a strong case for believing that the monitor switch was still good (please re-read if necessary).
But I have read some of your other posts and I am impressed with your knowledge and experience.
(...and generosity for sharing them so freely.)

Even so, you do not have the advantage of seeing and working with this particular device first hand.
Having bench tested the switch successfully, I do not see what could be wrong with it;
other than perhaps it doesn't switch "open" soon enough
(i.e. perhaps the door projections do not push the little button on the switch in far enough to open the circuit.)

I would like to run a test, if you think it is reasonable.
If I disconnect the wires from the monitor switch it will be like taking that switch out of the circuit, but the oven should still operate.
I would have to make ABSOLUTELY CERTAIN that the door is closed and remains closed during the test.
If the microwave oven operates without blowing the main fuse,
I would be very much convinced that the switch is the only problem and I will proceed to replace it with confidence.

Do you think this makes sense?
Thanks,
Chartman

 

[rickgburton]

OK, This is what I mean by over thinking it; I don't need all the extras. Don't make up your own tests. Don't stick wires in the connectors. Don't leave switches out of the circuit. Don't bench test anything. All you need to do is check each switch for continuity by opening and closing the door. To avoid any confusion remove all the wires from the switch you're testing. If the state of the switch doesn't change when opening and closing the door check if the door latch is activating the switch. If yes, replace the switch. If no, you you probably need to replace the switch bracket. Check each switch the same way.

 

[leinoffs]

Okay.
Thanks for the advice.