Recommended repair or magnetron replacement of broken microwave (Jenn-Air M170B)

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This Jenn-Air (model M170B) 1,350 Watt microwave just stopped heating:

I called Jenn-Air customer support who said there's no troubleshooting for when it doesn't heat. They said the magnetron may need to be replaced: Jenn-Air 800-536-6247 Customer Care
A replacement microwave oven has to fit over the electric oven:

Interestingly, (since it was above the oven) the back sticker says: "May be built into a cabinet structure, but not for use adjacent to (with 2 feet of) any gas or electric range, cooktop or oven."

But, that sticker also says: This microwave is approved for mounting directly over Jenn-Air wall ovens as follows: W2700 Series Using MK271 Trim Kit, W3000 Series Using MK301 Trim Kit
Having never worked on a microwave, I ask what the conventional wisdom is. Q: Is it generally feasible to replace just the magnetron? Q: Will similarly sized microwave ovens fit (22" widex13"tallx15" deep)? Q: Is it generally best to stick within the same brand? (e.g., JMC1116AB)?
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Probably just needs a new thermal cutoff. This random page has a picture.
<http://sell.lulusoso.com/selling-leads/648523/T1-11-BH2-thermal-cut-off . html>
You should find a schematic inside the unit after you take off the cover. With some basic electronic troubleshooting skills you can identify which of the 2-3 thermal cutoffs has gone bad. They're cheap and generic, but come in different temp ranges.
(Now, have fun turning this thread into a 500 post thread, while all the helpful people teach you how to read a schematic and use your multimeter, and arm you with enough info to write the internet's most definitive treatise on microwave oven repair.)
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On 12/17/2012 9:19 AM, Smitty Two wrote:

Check fuses and electrical connections. I had one where corrosion eventually overheated the connection on the door switch and disabled it. I've fixed a few microwaves, and almost all had bad diodes. Certainly possible, but I've never seen a bad magnetron.
Be aware that the big cap can hold enough charge to kill you after days and days being off. Even if you don't get electrocuted, you can be seriously injured when you fly across the room and bang your head on the counter. And you'll be scraping pieces of skin off the sharp edges of the case.
I don't know of a good DIY way to discharge the cap. I once made the mistake of shorting it with a wire. Scared the crap outa me when the wire exploded.
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On Mon, 17 Dec 2012 10:47:00 -0800, mike wrote:

I don't see any diodes yet; but I do see the big cap you speak of:

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The ones I've worked on, the diode is connected to the cap. Your diode might be going from cap to the case of the unit.
Christopher A. Young Learn more about diodes www.lds.org .
On Mon, 17 Dec 2012 10:47:00 -0800, mike wrote:

I don't see any diodes yet; but I do see the big cap you speak of:

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On Mon, 17 Dec 2012 18:07:35 -0500, Stormin Mormon wrote:

Ah, there was something there.

But it looks more like a rectangular ceramic resistor than a tubular diode.
I haven't measured it due to the warnings about the charge on the capacitor.
Today I looked at Lowes but they didn't have any black 22 inch by 13 inch microwaves. The size seems to be the biggest hurdle.
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On 12/17/2012 9:06 PM, Danny D. wrote:

That's the diode I saw in the pictures and the diagram. Diodes come in all shapes and sizes. ^_^
TDD
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On Mon, 17 Dec 2012 22:08:35 -0600, The Daring Dufas wrote:

Ah. Thanks. I'll figure out how to discharge the capacitor first. It has been sitting all day, so maybe by tomorrow it will have discharged. My Fluke DMM has a diode test mode, so I can at least run that baseline.
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On 12/17/2012 10:34 PM, Danny D. wrote:

The safest way is to use a 100k ohm resistor across the capacitor then check for residual voltage with your DVM. There is always The Jesus Method for discharging caps. ^_^
TDD
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<pants and wags tail> Cookie! Cookie!
http://morethanaminute.com/wp-content/uploads/2011/07/Cookie_Monster.jpg
Christopher A. Young Learn more about Jesus www.lds.org .

The safest way is to use a 100k ohm resistor across the capacitor then check for residual voltage with your DVM. There is always The Jesus Method for discharging caps. ^_^
TDD
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Should be infinite ohms one way, and then reverse the leads, and get some where between 2k (about that) ohms the other way. My SWAG at the moment is the diode went. If the diode shorted, the cap may be discharged now.
Christopher A. Young Learn more about Jesus www.lds.org .
On Mon, 17 Dec 2012 22:08:35 -0600, The Daring Dufas wrote:

Ah. Thanks. I'll figure out how to discharge the capacitor first. It has been sitting all day, so maybe by tomorrow it will have discharged. My Fluke DMM has a diode test mode, so I can at least run that baseline.
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Most digital meters will not bias a diode into conduction. That is why they have a didoe check on some of them. Even that may not check a microwave diode.

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On 12/18/2012 8:44 AM, Ralph Mowery wrote:

A microwave diode is a bunch of lower voltage diodes in series. I don't remember exactly how many, but a typical multimeter won't test it...unless it's shorted. Need more volts to forward bias it. 9V battery and a light bulb might do it. Two 9V in series probably will.
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On Tue, 18 Dec 2012 04:49:48 -0500, "Stormin Mormon"

Hehe. What good does "maybe" do??? ;-)
--
croy

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I was looking at what method Sam would use to test diode. I would simply hook 9 volt battery in series with diode and analog meter on high ohms.
On my mirror page..... http://zekfrivolous.com/faq/sam/micfaq.htm
Greg
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It gives you the option of not being killed?
Christopher A. Young Learn more about Jesus www.lds.org .
wrote:>Should be infinite ohms one way, and then reverse the leads, and get some

Hehe. What good does "maybe" do??? ;-)
--
croy



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Danny D. wrote:

Hi, Magnetron needs high voltage to function. That diode is HV diode some times in series to raise voltage rating. Usually Magntron buzzes when working. Is it silent when turned on? Also oven door has multi sequenced interlock switches which can go bad.
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On 12/18/2012 7:55 PM, Tony Hwang wrote:

NO!!!! DO NOT UNDER ANY CIRCUMSTANCES ASSUME THAT THE CAP IS DISCHARGED...EVER...!!! Mine was dead for a week and still had enough charge go explode the wire I shorted across it.
NO!!!! DO NOT UNDER ANY CIRCUMSTANCES ASSUME THAT THE CAP IS DISCHARGED...EVER...!!!
If you wanna risk blowing up your Fluke, you can measure the voltage on the cap...and possibly blow up your meter.
Death is final...don't risk it...no matter how small you think the risk.

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I WONDER. IF YOU TOOK A COTTON SWAB!!!! AND TAPED THAT TO A ***WOODEN STICK**** AND THEN DIP!!!! THE SWAB INTO WATER, AND PUT THAT

OF THE "CAPACITOR" WOULD =DISCHARGE= THROUGH THE ?MOISTURE? AND THAT WOULD BE ^SAFER^????
Christopher A. Young Learn more about Jesus www.lds.org .

NO!!!! DO NOT UNDER ANY CIRCUMSTANCES ASSUME THAT THE CAP IS DISCHARGED...EVER...!!! Mine was dead for a week and still had enough charge go explode the wire I shorted across it.
NO!!!! DO NOT UNDER ANY CIRCUMSTANCES ASSUME THAT THE CAP IS DISCHARGED...EVER...!!!
If you wanna risk blowing up your Fluke, you can measure the voltage on the cap...and possibly blow up your meter.
Death is final...don't risk it...no matter how small you think the risk.
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On 12/19/2012 3:37 AM, mike wrote:

I do believe I mentioned discharging the capacitor through a 110k ohm 1/2 watt resistor. O_o
TDD
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