# Microwave not heating - Bad magnetron?



## RuLEoF2 (May 5, 2017)

Hi all,

I'll apologize in advance for this being so long. I didn't want to risk leaving out any important details.

I'm troubleshooting my JVM1440WD003 space saver GE microwave that appears to be running normal but it's not heating anything. I eventually got the magnetron out and it doesn't look good. I don't know anything about magnetrons so I don't know if all the discoloration is "normal". The tiny bit of charring on the one side seemed to me like a pretty solid indicator but I really don't know.
















Before I got there, I tested several other items. 

1) Replaced the HV diode
2) Tested the door switches, all had proper continuity.
3) Checked the capacitor which is reading 0.90 uF.
4) Three out of four "thermostats" read 0.10 ohm

Now, here's where it gets sketchy. I've read several threads where people are saying that these devices that parts stores call "thermostats" are actually fuses or switches. That's where my confusion starts.

The fourth one reads open. That one goes on an internal cover for the magnetron/transformer compartment. I'm not sure if it's bad because I read on another forum that one of these thermal devices is supposed to be open at room temp and closes at 158'F which turns on the fan to keep the internal components from overheating when the stove is being used. I did two tests to try and find out if the open thermostat is the one that the guy was talking about.

1) I shorted the blade connectors going to the suspect thermal fuse and that did run the fan. 2) I heated the fuse up to around 170'F and it did not close. So, now I'm wondering if it _is _actually bad and hasn't been doing it's job of cooling the magnetron and could be why it looks so toasty.

I haven't tested the transformer because honestly, I'm not sure how. The videos I've seen show people checking a secondary coil terminal on the back and mine doesn't have one. Just two in the front for what I'm assuming is the primary coil with heavy gauge winding. I did do some testing but I really don't know what those results mean. So, I'll post them here and maybe someone here can analyze them for me. See photo for reference.

1) From terminal to terminal I get 0.40 ohms
2) From either terminal to ground is open
3) From any red wire to either terminal is open
4) From any red to ground is open
5) From any red to red is 0.10 ohms
6) From white wire to ground or either terminal is open
7) From white to red is open









Finally, last part that I'm concerned about is the "stirrer motor" which is in ceiling of the microwave chamber. Since it works with the magnetron, I'm wondering if it could be damaged too.

Again, sorry for the really long read. Any advice would be greatly appreciated.

Thanks you.


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## Missouri Bound (Apr 9, 2011)

Let me say that I admire your willingness to take it apart and try and fix it. I have done the same thing over the years to just about everything I have owned.
Many were successful, some were not.
That being said....the replacement magnetron for that machine is going to cost between $150 and $200.
You can replace the microwave for that.
But if you still want to tinker, be careful. An energized magnetron is a very dangerous piece of electronics.


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## RuLEoF2 (May 5, 2017)

Missouri Bound said:


> Let me say that I admire your willingness to take it apart and try and fix it. I have done the same thing over the years to just about everything I have owned.
> Many were successful, some were not.
> That being said....the replacement magnetron for that machine is going to cost between $150 and $200.
> You can replace the microwave for that.
> But if you still want to tinker, be careful. An energized magnetron is a very dangerous piece of electronics.


Hi there. Thanks for taking the time to read my ridiculously long post. lain:

Actually, I just bought a factory magnetron that comes with a diode on Amazon for $34.

I will try to fix just about anything. Including my cars. If I know I can fix it for 50% or less of the cost of a new one, I will usually go for it. But, ultimately, it's a judgement call based on the overall condition of the item that I'm fixing.


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## Missouri Bound (Apr 9, 2011)

RuLEoF2 said:


> Actually, I just bought a factory magnetron that comes with a diode on Amazon for $34.
> .


Well you got me there. I looked at a appliance repair parts source before I responded to your post. I didn't think to look at Amazon.
Kudos to you for price shopping.
The one thing I would be concerned about is that microwaves can leak if not re-assembled properly. There are plenty of testers out there and some novel ways of testing. You may want to look at that as well.
Good luck.


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## RuLEoF2 (May 5, 2017)

Missouri Bound said:


> Well you got me there. I looked at a appliance repair parts source before I responded to your post. I didn't think to look at Amazon.
> Kudos to you for price shopping.
> The one thing I would be concerned about is that microwaves can leak if not re-assembled properly. There are plenty of testers out there and some novel ways of testing. You may want to look at that as well.
> Good luck.


Yeah. I know people that refuse to buy from Amazon because they don't want to support the juggernaut but I can't bring myself to pay 500% more buying elsewhere solely on principal. "Big A" has saved me so much money on car parts that I could have bought a third car.

I definitely know to be careful when dealing with HV equipment. I build and repair aircraft radar systems so high power electronics is what I do. Radar is all microwave energy. 

The leak check is an excellent tip. I know lots of test techs that I should be able to barrow a leak tester from.

Thank you. :wink2:


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## BayouRunner (Feb 5, 2016)

Sounds like the limit switch on the magntron is bad. If the magnetron got hot the limit switch would open then the microwave would quit heating. I would temporarily jump that limit and see if the microwave works. If it does replace the limit switch


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## RuLEoF2 (May 5, 2017)

BayouRunner said:


> Sounds like the limit switch on the magntron is bad. If the magnetron got hot the limit switch would open then the microwave would quit heating. I would temporarily jump that limit and see if the microwave works. If it does replace the limit switch


The one on the magnetron is one of the three that has continuity and is showing 0.10 ohms.

So, you think that the magnetron is ok, despite the discoloration?


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## Dread-Scott (Mar 1, 2020)

I have a three year-old Bosch that did the same as yours. Just stopped heating but everything else was working. Read a lot on the internet and watched a few youtubes. Like you, I like a good challenge so decided to try the repair on my own. Fuse testing was easy so moved on to the capacitor. Mine spec’d out ok but I decided to replace it anyway- $9.00 on Amazon. The mag and transformer were $150 and $200 respectively. Even though the capacitor checked out ok, that was my problem. Fixed for $9.00. Win! Recommend replacing the capacitor if yours is an inexpensive part. Good luck!


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## Druidia (Oct 9, 2011)

Dread-Scott said:


> I have a three year-old Bosch that did the same as yours. Just stopped heating but everything else was working. Read a lot on the internet and watched a few youtubes. Like you, I like a good challenge so decided to try the repair on my own. Fuse testing was easy so moved on to the capacitor. Mine spec’d out ok but I decided to replace it anyway- $9.00 on Amazon. The mag and transformer were $150 and $200 respectively. Even though the capacitor checked out ok, that was my problem. Fixed for $9.00. Win! Recommend replacing the capacitor if yours is an inexpensive part. Good luck!



I wonder how that happens - a part tests out ok yet replacing it fixes the problem. 

That happened to my microwave oven too. It wasn’t a heating problem. The turntable was turning and the fan was on when the door was opened. The door microswitches tested ok but I still replaced them because a pair of them was just ~$8 on Amazon. It fixed the problem.


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## Missouri Bound (Apr 9, 2011)

Druidia said:


> I wonder how that happens - a part tests out ok yet replacing it fixes the problem.


That happens all the time. In most cases it is something that came loose and was inadvertently repaired when re-assembled.


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## Druidia (Oct 9, 2011)

Missouri Bound said:


> That happens all the time. In most cases it is something that came loose and was inadvertently repaired when re-assembled.



In my case it wasn’t something loose or because of dirty contacts. The door switches, that the multimeter said were ok, didn’t fix the problem even after I cleaned them and put them back in (I also cleaned everything in the control panel where the switches are). I replaced them with new switches and that fixed the problem.


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## RuLEoF2 (May 5, 2017)

Dread-Scott said:


> I have a three year-old Bosch that did the same as yours. Just stopped heating but everything else was working. Read a lot on the internet and watched a few youtubes. Like you, I like a good challenge so decided to try the repair on my own. Fuse testing was easy so moved on to the capacitor. Mine spec’d out ok but I decided to replace it anyway- $9.00 on Amazon. The mag and transformer were $150 and $200 respectively. Even though the capacitor checked out ok, that was my problem. Fixed for $9.00. Win! Recommend replacing the capacitor if yours is an inexpensive part. Good luck!


That was a great call. You definitely lucked out. 

I hate sending things to the dump when they can be fixed. It's not just about saving money for me. I guess its kind of a tree-hugger thing. I know it seems futile but I see it as everything that I reuse, repair, re-purpose or give to someone else is one less thing adding to the pile that shouldn't be there in the first place. If I can do that and save money too, double win.

If I can find a cap that cheap, I will definitely consider replacing that too. Thanks for the tip.




Druidia said:


> I wonder how that happens - a part tests out ok yet replacing it fixes the problem.
> 
> That happened to my microwave oven too. It wasn’t a heating problem. The turntable was turning and the fan was on when the door was opened. The door microswitches tested ok but I still replaced them because a pair of them was just ~$8 on Amazon. It fixed the problem.


It's frustrating and elating all at the same time. I've been there too. You're annoyed that you can't find the problem but when your experimental attempt fixes it for only a few bucks, you're like "YEAH!" But then, if you're like me, there's still that nagging little sense of failure that you never really found the problem and you don't know why. Ultimately, you just have to say "Oh well, fixed is fixed" and be happy with that.

Good job on your repair. It's Miller time when you get a win that easy.


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## Druidia (Oct 9, 2011)

RuLEoF2 said:


> It's frustrating and elating all at the same time. I've been there too. You're annoyed that you can't find the problem but when your experimental attempt fixes it for only a few bucks, you're like "YEAH!" But then, if you're like me, there's still that nagging little sense of failure that you never really found the problem and you don't know why. Ultimately, you just have to say "Oh well, fixed is fixed" and be happy with that.
> 
> Good job on you're repair. It's Miller time when you get a win that easy.


Yes, I was super elated because I wasn’t really looking forward to getting a new microwave oven - mainly because I have a large OTR microwave oven that tiny me with my puny arms wouldn’t be able to remove by myself. It was already 16-YO that time so it dying wouldn’t be a surprise considering so many other MOs die young. 

I keep telling my MO what a good girl she is. HA HA HA.


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## huesmann (Aug 18, 2011)

Druidia said:


> I wonder how that happens - a part tests out ok yet replacing it fixes the problem.
> 
> That happened to my microwave oven too. It wasn’t a heating problem. The turntable was turning and the fan was on when the door was opened. The door microswitches tested ok but I still replaced them because a pair of them was just ~$8 on Amazon. It fixed the problem.


I picked up an OTR microwave from Craigslist free stuff. The PO said all the buttons worked, it just wouldn't turn on and cook. I figured the problem must be one of the door switches, so I started disassembling. The case came off, which gave me a good look at the switches. They all seemed to be in OK shape, the little switch stubs depressed and released OK. Then I moved to the latch mechanism. It seemed a little loose, so I opened the door panel up. Aha! The piece on the door frame where the latch spring mounts had broken off—probably someone had slammed it shut or something—and the spring was gone, so the latch was not contacting the switches properly. I used some hot glue to glue the mount back in place, with plenty of extra glue buildup for reinforcement. That, plus a $6 spring put me in business.


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## RuLEoF2 (May 5, 2017)

huesmann said:


> I picked up an OTR microwave from Craigslist free stuff. The PO said all the buttons worked, it just wouldn't turn on and cook. I figured the problem must be one of the door switches, so I started disassembling. The case came off, which gave me a good look at the switches. They all seemed to be in OK shape, the little switch stubs depressed and released OK. Then I moved to the latch mechanism. It seemed a little loose, so I opened the door panel up. Aha! The piece on the door frame where the latch spring mounts had broken off—probably someone had slammed it shut or something—and the spring was gone, so the latch was not contacting the switches properly. I used some hot glue to glue the mount back in place, with plenty of extra glue buildup for reinforcement. That, plus a $6 spring put me in business.


A spring? Interesting. I took the whole latch/switch assembly out to test the switches and give it a good cleaning. I didn't see any springs. Just latches that moved freely. I'll take a closer look at the parts diagram. Maybe I'm missing one too. Thanks.


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## huesmann (Aug 18, 2011)

This is the latch in mine:










Pic shows it sideways, but it goes vertically. The two pegs on each end (one interior one exterior) are retained in two holed tabs on the door frame. The little notched bit in the middle of the latch holds one end of the spring, there's a similar bit on the door frame for the other end of the spring. When you close the door, the hooks ride up and down against the latch stops in the cabinet. The spring returns the latch to the down position, and the hooks contact the door switches to open (or close, not sure) the circuit, telling the microwave the door is closed. Without the spring there, the latch didn't give enough pressure to the switches.


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## Dread-Scott (Mar 1, 2020)

I began searching online for the capacitor using the Bosh microwave model number and discovered that the online parts stores were all back-ordered. I then looked at the markings on the capacitor itself and used that info for my parts search. It is a Chinese manufactured unit named BiCai. Plenty of all different specs on Amazon and eBay. 

Best wishes for a successful repair!


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## RuLEoF2 (May 5, 2017)

Druidia said:


> Yes, I was super elated because I wasn’t really looking forward to getting a new microwave oven - mainly because I have a large OTR microwave oven that tiny me with my puny arms wouldn’t be able to remove by myself. It was already 16-YO that time so it dying wouldn’t be a surprise considering so many other MOs die young.
> 
> I keep telling my MO what a good girl she is. HA HA HA.


Well, your success inspired me so I just tested the switches. I used a set of hook leads with my Fluke and put them on the termainals of each switch. Then opened and closed the door a few times. The results are somewhat interesting.

This model has three switches on the latch assembly. Two push-to-close (PTC) and one push-to-open (PTO). All are operating normally with solid continuity. However, the two PTC switches measure a consistent 0.10 ohms with the door closed and the one PTO fluctuates from 150.00 to 9.00 ohms with the door open. If either of the PTC switches did that I would say there it is, bad switch. But I would think that high resistance on the PTO is irrelevant since it's supposed to be open with the door closed. 

If that high resistance made the control board think that the switch was open when it was actually closed, I could see that being an issue but it would only affect function with the door open. At least that's the way I would interpret it.

Anyone, please correct me if I'm wrong.


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## RuLEoF2 (May 5, 2017)

Dread-Scott said:


> I began searching online for the capacitor using the Bosh microwave model number and discovered that the online parts stores were all back-ordered. I then looked at the markings on the capacitor itself and used that info for my parts search. It is a Chinese manufactured unit named BiCai. Plenty of all different specs on Amazon and eBay.
> 
> Best wishes for a successful repair!


Yeah. I searched by GE part number and found generics fairly cheap. One on Amazon for $15.99 and one on Ebay for $11.99. I didn't think to search by spec so I'll try that too.

Thanks.


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## RuLEoF2 (May 5, 2017)

BayouRunner said:


> Sounds like the limit switch on the magntron is bad. If the magnetron got hot the limit switch would open then the microwave would quit heating. I would temporarily jump that limit and see if the microwave works. If it does replace the limit switch


Although the magnetron thermal cut-off switch doesn't appear to be bad because it is reading 0.10 ohms at room temperature, you do bring up an interesting question. 

Even if the fan thermal switch is bad and didn't close at high temp, the magnetron cut-off should have tripped if the magnetron overheated thus deactivating it. Is it possible that the magnetron cut-off is opening prematurely under power and closing when de-energized? I guess that only way to know is to try your jumper idea after all. :smile:


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## RuLEoF2 (May 5, 2017)

Mag cut-off good or bad, I'm still really concerned about that open fan thermal switch and the toasted magnetron. Even if the jumper works and I get function back, should I replace the magnetron anyway?


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## RuLEoF2 (May 5, 2017)

BayouRunner said:


> Sounds like the limit switch on the magntron is bad. If the magnetron got hot the limit switch would open then the microwave would quit heating. I would temporarily jump that limit and see if the microwave works. If it does replace the limit switch





RuLEoF2 said:


> Although the magnetron thermal cut-off switch doesn't appear to be bad because it is reading 0.10 ohms at room temperature, you do bring up an interesting question.
> 
> Even if the fan thermal switch is bad and didn't close at high temp, the magnetron cut-off should have tripped if the magnetron overheated thus deactivating it. Is it possible that the magnetron cut-off is opening prematurely under power and closing when de-energized? I guess that only way to know is to try your jumper idea after all. :smile:


Just gave it a go. The jumper had no effect. It was worth a shot though. Thanks for the suggestion.


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## RuLEoF2 (May 5, 2017)

Just made a new discovery. I was watching some more troubleshooting videos and found one for testing the capacitor. Up until now, I only tested it for capacitance which read 0.90 uF. Only 0.01 above the max which I was told was close enough by a professional electronics test technician. I did not test resistance or continuity as suggested by the video I just watched.

Continuity between terminals and either terminal to body reads open. As for resistance, this is where it gets interesting. The label on the cap body says 10M ohms. What's interesting is that when I hold the test leads on steady, I get an unstable reading that starts low and climbs to almost 7.0M ohms and then reads open. The longer I wait between tests, the lower the starting reading is. A couple minutes and it starts as low as 1.5M. If I only wait 10-15 seconds it starts around 5.0M but always open just before it hits 7.0M.

Now, if I put the leads on and remove them for less than a second and put them back on, it sometimes jumps up to around 15M and then falls or starts around where I was at and climbs again. It will eventually settle between 9.87M and 9.89M where it stabilizes.

Does anyone know what this means?


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## RuLEoF2 (May 5, 2017)

Decided to give the HV diode another look. 

Going with what I had read and the videos I watched, the diode sounded like the most likely offender. Seemed like a good place to start so I bought a pair of new ones and installed one on Saturday. Obviously, it didn't fix the problem. I've tested almost everything else and no real answers yet, maybe I got bad diodes.

Using a 9V battery measuring 9.47v, I tested all three. The original, the new one that I installed and removed and the other new one fresh out of the bag. The two new diodes read about 5.65v and slowly falls. They barely show 0.001v in reverse. The original diode reads around 6.40v and slowly rises. That one shows 0.010v in reverse. 

Next, I tried using the diode tester setting on two separate Fluke meters and all three diodes tested open in both directions.

Any thoughts?


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## RuLEoF2 (May 5, 2017)

Confirmed that the one open thermal switch is normally open. I used a meat thermometer, heat gun and multi-meter to test it multiple times. It closes at around 190'F which would then activate the fan. Resistance fluctuates but stays under 1.0 ohm.

After thinking about it, the placement of that switch seems wrong to me. I found it on the transformer cover and a cut-off thermal switch on the base panel just below the control board. What I read in another forum thread was that the fan switch was below the board on their model which makes sense. The electronics is going to be the most sensitive to heat so you would want your best heat protection there. 

So, I'm beginning to suspect that the previous owner may have worked on this microwave before and mistakenly swapped the switch locations. The wires are long enough to go either way.

Does that make sense to anyone else?


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## RuLEoF2 (May 5, 2017)

RuLEoF2 said:


> ...I get an unstable reading that starts low and climbs to almost 7.0M ohms and then reads open. The longer I wait between tests, the lower the starting reading is. A couple minutes and it starts as low as 1.5M. If I only wait 10-15 seconds it starts around 5.0M but always open just before it hits 7.0M.
> 
> Now, if I put the leads on and remove them for less than a second and put them back on, it sometimes jumps up to around 15M and then falls or starts around where I was at and climbs again. It will eventually settle between 9.87M and 9.89M where it stabilizes.



Did some more research. My test results are normal and indicate that the capacitor is working properly.


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## RuLEoF2 (May 5, 2017)

I guess I've scared everyone off with all my rambling because I haven't gotten any replies lately. I've done some small tests and re-tests and some of my results have changed. So, I thought summarize my current findings and hopefully draw some new support.

1. HV diode - OK
2. HV capacitor - OK
3. HV transformer - OK
4. Thermal switches (4) - OK
5. Door switches - OK
6. Main fuse - OK

The magnetron tests OK with my multi-meter but doesn't look good with some blackening of the RF gasket and the significant discoloration of the antenna. No cracks in the magnets that I can see. Other than some oil vapor buildup on one side of the radiator. That's it.

















Any thoughts or suggestions on what else I could try?

Thank you.


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## huesmann (Aug 18, 2011)

RuLEoF2 said:


> I guess I've scared everyone off with all my rambling because I haven't gotten any replies lately.


I think it's because most of us would have tossed the nuke box by now. :biggrin2:


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## Missouri Bound (Apr 9, 2011)

RuLEoF2 said:


> I guess I've scared everyone off with all my rambling because I haven't gotten any replies lately.


Not me. You are doing the work and research.
Nothing to reply to or comment on until you either fix it or toss it.
We are waiting on you and your repairs.:vs_coffee:


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## RuLEoF2 (May 5, 2017)

huesmann said:


> I think it's because most of us would have tossed the nuke box by now. :biggrin2:


Yeah I know, but money is a little tight right now and if I can fix it, that would be preferred.



Missouri Bound said:


> Not me. You are doing the work and research.
> Nothing to reply to or comment on until you either fix it or toss it.
> We are waiting on you and your repairs.:vs_coffee:


Since the magnetron is the only thing that shows any sign of damage, I ordered one and it's on the way. I'm just throwing the net out hoping to catch some new ideas on what else I could try or test.

I'll update when something changes. In the meantime feel free to check out this video tour of the microwave. Maybe you'll see something that I missed.






Thank you guys. :smile:


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## Missouri Bound (Apr 9, 2011)

I think a lot of people would bite the bullet and change out the microwave.
Personally...I would probably go the route you have gone, since I tend to take everything apart and do the repairs myself. I spent a few decades as a HVAC / maintenance guy and nothing was off limits. What people throw out that can be easily repaired would amaze you.
I have repaired water heaters with a $20 thermostat....the owner paid someone to replace the heater with a new one......$600.
I have repaired washing machines, dryers, and yes a few microwaves, nothing as deep as you are going though.
It's all good. Whether you get it fixed or not you will have gotten a good learning experience from this effort. That is worth more than driving to the store and getting a new microwave.


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## RuLEoF2 (May 5, 2017)

Missouri Bound said:


> .
> ..What people throw out that can be easily repaired would amaze you.
> I have repaired water heaters with a $20 thermostat....the owner paid someone to replace the heater with a new one......$600.
> I have repaired washing machines, dryers, and yes a few microwaves, nothing as deep as you are going though.
> It's all good. Whether you get it fixed or not you will have gotten a good learning experience from this effort. That is worth more than driving to the store and getting a new microwave.


Yeah, I've been the benefactor of prematurely dispatched items many times. Usually, it's a minor repair that doesn't even need parts. Just a tweak here and a patch there, some clean up and it's like new again.

As for this whole effort, that's exactly how I look at it. It's knowledge and experience that hopefully through this forum, someone else can benefit from as well.


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## RuLEoF2 (May 5, 2017)

VICTORY!!!

New magnetron/diode kit arrived early. Just put it in an and there it is. Hot water again.

* Parts... $35
* Troubleshooting... That kinda sucked but I learned a lot about microwaves.
* Not having to go out in the middle of a pandemic to spend $300 on a new microwave.... 

PRICELESS


Thank you again gentlemen. I genuinely appreciate you taking the time to keep me company on this one.

Take care. Be safe, be healthy.


Dave


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## huesmann (Aug 18, 2011)

Excellent news!


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