No power to GE microwave JVM1540LM1CS

by Larry
(Philadelphia Pa)

The ceramic in-line fuse tests ok., and the door switches check out ok. Four thermostats are located within the unit--one is what they used to call the flame arrestor and is located in the top of the unit pointing downward and shows continuity (#AP3994055), one is on a bracket attached to the side of the magnetron and shows no continuity (#AP4344046), one is attached to the bottom panel and shows no continuity (part # is the same as the one attached to the magnetron), and the fourth is attached to the bottom panel adjacent to the one just mentioned--this one shows continuity (#AP3994357). Perhaps I am barking up the wrong tree but I thought that all four of these thermostats should show a continuity, but the two with the same part # are open. Would this be a coincedence, and if open would this shut all power off to the unit, or could it be another issue. any comments would be greatly appreciated---Larry






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Answer

Hi Larry,

On every microwave I have ever worked on the thermostat on the magnetron tube should be closed (continuity) and if not it is bad. I agree it does sound a little odd that the same switch would be open, it sounded so odd that I looked at 5 service manuals (couldn’t find one for your exact model) for similar GE models and they all indicate that the thermostat should be closed. As far as I know it has always been like that unless it is different for your model. I suggest replacing the thermostats and go from there.


Thank you,
Shawn/administrator

Comments for No power to GE microwave JVM1540LM1CS

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Bad Diode
by: Larry

As an update to my original post I tested the diode and found I was getting no resistance readings from swapping both end leads. I did test the capacitor and found that to be ok. So I will try a new diode and replace the two thermostats---so far this will not be a pricey fix, and hopefully by doing this little bit of magic to the unit it just might work????

More To Note
by: Shawn

One more thing you should note is that there is a hood thermostat that will read open (no continuity) normally but the part number shouldn’t be the same as the one on the magnetron tube unless there is a mistake with the parts breakdown or you are looking at it wrong.


Also the diode is most likely not the problem but the test you did would suggest that it is bad. However a lot of ohmmeters will not test microwaves diodes because the resistance is too high in which case you would get a false negative test results.

Thermostat #'s
by: Larry

Shawn--I just rechecked the schematic on AppliancePartsPro.com and the magnetron and hood thermostats are listed as the same #110 (both of these tested open) --part # AP4344046---so could the diagram be incorrect??

Larry

RE
by: Shawn

I just took a look at the parts breakdown on GE’s official website and yes the part number for two of the thermostats are the same. One of the thermostats I know for sure is the magnetron tube thermostat but I don’t know what the other one is because all the description says is thermostat.

Without a service manual or a wiring diagram to your exact model (which I don’t have) I can’t tell you for sure but I think the magnetron tube thermostat should have continuity. I have a wiring diagram for six different GE microwaves and they all indicate that the magnetron tube thermostat should have continuity. If for any reason this model happens to be different replacing the thermostat will be a waste of time and money.

I have checked many magnetron tube thermostats and none of them have been bad and all of them had continuity. I have never seen this thermostat bad so I can only assume they don’t go out very often being that I have worked on 1000s of microwaves. That is not to say yours isn’t bad because I still think it should have continuity unless your wiring diagram indicates differently.

If it turns out that I am wrong please let me know for future knowledge.

Another thing to note is that since the part number is the same, if it is the thermostat both of them are bad. Which seems unlikely but these thermostats are there for safety. So if something overheated both thermostats could have blown before it cooled off.

One more thing
by: Shawn

I just realized when I looked it up that it is a counter top model so there is no hood thermostat.

Replace both of those thermostats.

Over The Range microwave
by: Larry

Scott--FYI--this microwave was removed from over a cooktop stove---

RE
by: Shawn

Then there is a hood thermostat but I don’t know why it came up as a counter top model when I looked it up.

A Semi Miracle
by: Anonymous

Hi Shawn---well, today I rec'd the two new thermostats and diode. I replaced only the magnetron thermostat and the unit fired up and all of the keypad controls functioned normally--all except the unit will not heat!!! So then I replaced the bottom panel thermo. with the same matching # as the magnetron thermo. and everything performed except the fan would not shut off?? So I put the old thermo. back on and the fan shuts off normally, except there is still no heat!! The old thermo. in the bottom panel may have reset itself as initially I found it open, but now is showing continuity.

The diode--I bench tested the new diode and it read the same as the old one--apparently my ohmmeter is showing a false positive, so I did install the new one.

This leaves me with no heat?? I could keep throwing $$ at this thing--a new magnetron??

After removing the panel there was no schematic anywhere inside--I thought this unusual??

I do appreciate the time you spend with me, and the website. In fact, I may make a contribution in the very near future!! Of course you are dealing with the guy who reuses dental floss--LOL!!

Magnetron
by: Anonymous

For what its worth---the magnetron does show continuity??

RE
by: Shawn

The parts breakdown was wrong because those thermostats should be different part numbers, which is what caused confusion on my part.

When a magnetron tube goes bad it will sometimes over heat and that is most likely what caused the thermostat to trip. It must be pretty bad because typically it will not trip even with a bad magnetron but that is what I believe the problem is. See that other thermostat is to turn the fan on when it overheats hints why the fan will not turn off.

When I was thinking that both thermostats were bad I didn?t think the magnetron tube had caused the problem because it would be unlikely for the magnetron to cause both thermostats to trip.

Continuity across the magnetron really doesn?t tell you anything. Look around the magnetron area to see if there are any burnt looking spots which would be a dead give away for a bad magnetron tube.

Check your owner?s manual because on some models the magnetrons have a parts warranty for ten years, some have a five year warranty and some just have one year warranty.

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