microwave oven saga

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Our GE JEM25DM3BB 1.0 cubic foot microwave oven crapped out recently and we couldn't find a suitable substitute. The oven functions would work, but it wouldn't heat. The problem is the microwave fits inside an enclosure of our kitchen cabinetry. When we moved into the house eight years ago there was another microwave there which died a couple years later. We had trouble finding a replacement then, but the GE barely fit in there. Now that GE model is discontinued and the only ones with dimensions small enough to fit are 0.7 cubic foot or less. The wife was not pleased with the choices.
My first option was to cut out the enclosure a bit more to get a normal sized microwave in there, but a woodworking friend pointed out it would look funny because the hole would extend all the way up to the bottom of the cabinet door above it. The wife was not pleased with that choice either.
My next option was to repair the one we have. After researching microwave ovens, the troubleshooting guides pointed to the overvoltage diode and the magnetron as the likely suspects for the symptoms of this oven. I disassembled the oven and took out the items. The diode was open in both directions so I immediately suspected it. I checked the magnetron for continuity and the leads had 0.000 ohms resistance between them. Hmm, that looks bad too. The high voltage capacitor seemed to be charging and discharging when I put the multimeter leads on it. I ordered the parts with next day delivery and the total was more than $200. Ugh...
When the new parts arrived I immediately ohms checked them and found the very same results as the ones I took out -- the diode was open in both directions and the magnetron was shorted. This time I was not pleased!
Facing no other options I went ahead and installed the diode first and heated up a cup of water for a minute. Still cold. Next I installed the magnetron and held my breath while I heated up the cup of water. After half a minute I noticed steam inside! When I took out the cup after a minute it was hot. I showed the cup to my wife and this time she was pleased. The microwave oven is back in the kitchen cabinet and working fine. Warming up leftovers in a pan or heating up the leftover morning coffee were good incentives to get this resolved.
I'm still baffled as to why the diode has no continuity. Is it because my 9-volt multimeter doesn't have enough current to get through the junction? I don't understand the magnetron properties so perhaps ohms checking it was a useless test.
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On 02/16/2016 12:28 PM, badgolferman wrote:

Glad you got it fixed.
Though I'm good with electronics I don't profess to be a microwave expert, but since that's an over voltage diode it would have to have some kind of series resistance which evidently was off scale for your meter (Could be as high as 200k in the forward direction)
As to the filament on the magnetron, I'd expect it to be under one ohm
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On 2/16/2016 11:28 AM, badgolferman wrote:

Bottom line: built ins/ons eat your lunch, sooner or later! We removed the (suspended) over-the-oven microwave when we removed the upper cabinets (oven is in peninsula so these things just boxed the kitchen in). For a while, we kept it on a counter -- wasting precious counter space!
We have since opted to move it to a small cupboard which gets it off the "counter circuit" and onto its own dedicated circuit. Also means we can replace it at will!

Be thankful they'd even *sell* you spares! :<

The diode will look like a reasonably HIGH impedance. It's operating at a few KV -- not the 9V your DMM is probably using.
The maggie will look almost like a dead short. Is your DMM truly accurate to 3 digits? I.e., is that 0.000 really 0.000 or more like 1.0?
You should also check each of the maggie's leads to case to verify there isn't a short, there.

You could have monitored load current to the maggie (limiting it through a resistive load so you can just watch the drop across that "ballast").
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step one..
I know what I am doing and I would not poke around inside a microwave that was powered up. You should not either. No joke, the voltage in thee are leathal.
step two there are DIY sites on the net that tell you how to test an HV diode with the power off.
Yes a high voltage diode will test open with a standard vom.
yes the two filament leads will look like a short. but they should not be shorted to the case.
read a few diy sites and keep the power off.
M
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On 2/16/2016 3:05 PM, snipped-for-privacy@yahoo.com wrote:

No, it's more than just "keep the power off". Energy is stored in the HV section (capacitor doubler). The circuit *may* have been designed with a bleeder to discharge the cap, over time.
But, the device is NOT WORKING. So, you can't assume any of the things that were designed to protect you are functioning correctly, either! (does "no user serviceable parts inside" ring a bell? :> )
I work with electricity all day -- and still treat it like a youngster who just got zapped for the first time! It's not like setting your hand on a hot stove -- where you MIGHT have a chance to correct your mistake before incurring some serious injury... (electrons are fast little devils!)
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On Sat, 22 Mar 1969 14:05:04 -0800 (PST), snipped-for-privacy@yahoo.com wrote:
replying to Tom Billings , robertjones wrote:

I just purchased a new set of tires, but there is still some ice and snow on the ground, and a lot of potholes in the roads. I was going to get them installed on my car, but after reading this, I decided that maybe I should wait a few more weeks. told the guys at the tire garage to hold off on installing them for now, and just brought the tires home. How long should I wait to install them?
Robert J.
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On Sun, 06 Mar 2016 23:37:07 -0600, robertjones

Your life is at risk driving on your old tires. In the winter, I get new ones every month. You heard the man, your tires are junk. Put them on today and get another set in mid April.
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On 03/07/2016 04:05 AM, Ed Pawlowski wrote:

I'll be glad to help your dispose of your old tires -- if they fit any of my vehicles. :)
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On 03/06/2016 11:37 PM, robertjones wrote:

You can safely disregard that post from 1969
In those days they had snow tires and by Spring, they'd melt.
Now they make tires from synthetic rubber
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Don Y wrote:

Only if I turn it upside down! This is what I was looking at.
https://drive.google.com/file/d/0B4RyxiIh1BYbX21yaXRiVXQtc2M/view?usp=sharing
https://drive.google.com/file/d/0B4RyxiIh1BYbRXhUTmo3eG9pWW8/view?usp=sharing
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On 2/17/2016 7:32 AM, badgolferman wrote:

Sure *looks* like a short! :>
If you still have it, you might check leads to case to see if the coil failed internally.
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On 2/16/2016 1:28 PM, badgolferman wrote:

For whatever reason, I've also gotten the open circuit reading on microwave diodes. The line at the bottom, you got your machine going. And made your wife happy. Way to go, man!
--
.
Christopher A. Young
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Stormin Mormon wrote:

This was nothing compared to taking out the window motor of my car and retraining the automatic stop.
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On 2/17/2016 9:34 AM, badgolferman wrote:

Yes, those are miserable. You da man! More success.
--
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Christopher A. Young
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The diode is usually made of several diode junctions in one case. Therefore it takes several volts to make it show up on most multimeters. The 9 volts of your meter may be enough voltage to break down the junctions and show something, however most do not apply the total 9 volts to the circuit. Most less than one volt as not to make diodes show up as a low resistance in one direction and very high in the other. Some meters will have a diode function that applies several volts to the leads to test many of the diodes of up to 1000 volts or so. This is still not usually enough for the mcrowave diodes.
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On Tue, 16 Feb 2016 18:28:00 +0000 (UTC), "badgolferman"

No. It doesn't have enough voltage. 9 volts is not enough to get through some diodes. Especially since you call it an over-voltage diode, t hat sounds like it shouldn't be passing any current unless the voltage is too high. 9 volts is not too high!
So how much was the magnetron and how much the diode? I'd think the diode was much less.

In general it's best to check voltages during operation, rather than resistance when standing still, but the one place this is almost impossible** is with a microwave. If you run it with the cage off the microwaves will harm you, especially the liquid in your eyeballs I hear.
I hope you were careful to assemble the metal cage around the microwave parts exactly as it was originally. My old one made about 1965, had a woven metal gasket, which woudln't let electromagnetic waves through, but I don't know what is used now.
**The way to do this would be to solder wires to the places you want to measure and if possible run the wires outside of the microwave cage without causing a leak and do the measurements when it's running but fully shielding those nearby.
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Micky wrote:

The magnetron was $161 and the diode was $35 + $25 next day air shipping. I could have gotten cheaper ones on Amazon but it would have taken longer to get them. This place also had a return policy so long as I didn't install the part. When I first installed the magnetron I used rubber washers to keep the screws from marring the installation tabs in case I needed to return it.
Considering the closest sized microwave I could find was $240 and the fee I would pay for a carpenter to modify the kitchen cabinet, I think this worked out more cost efficiently.
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On Wed, 17 Feb 2016 14:38:42 +0000 (UTC), "badgolferman"

Wow. I don't know any place that takes back electrical parts.

Partly for this reason, although I agree if nothing changes, you should be able to fairly declare that you didnt' burn it out. 99% certainty.

My brother burned out the microwave by putting in a metal rack that looked almost identical to the rack that was supposed to be there. He's supposedly known for mistakes but this one would have been easy to make (whoever washed it should have put the right one back in the microwave. That was probably the nanny/maid who was washing things all the time, and maybe she would have with enough time.). There was burn damage to a plastic shelf peg, so I'm sure it was the rack.
I arrive for a visit and between visits and meals I'm looking for tools and taking it apart, and I tell my sister in law I might be able to fix it but she insists on buying a new one. The old one has a blown fuse inside, a simple glass fuse, but I have no car. There's a party that night at their house (related to the reason I was visiting) so I hide the big microwave on the floor behind the wet bar between the kitchen and the front hall/mini-living room.
The next day the microwave is gone. I find it out by the garbage, replace the fuse, it works, so I borrow a car and take it to Goodwill. My sister-in-law has already hired a Mexican/handyman/carpenter to redo the facade in front of the microwave area. A much smaller effort than yours would have been, but combined with the MW itself, this is one of many reasons related to her that my brother is well over 65 and still working. What she doesn't know about money would fill an ocean.
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On Tue, 16 Feb 2016 18:28:00 +0000 (UTC), "badgolferman"

This is one reason I dont like the idea of built in appliances. Whether it's a microwave, range, dishwasher or anything else, sooner or later it will need to be repaired or replaced. It's hard or impossible to find a replacement that will fit. And if parts are even available, they cost more than a new appliance. Of course if your home comes that way, you're stuck with it.
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snipped-for-privacy@unlisted.moo wrote:
Ex, I see you caused AIOE to banlist the other group. Be careful what you do here. Hope you make it back there some day.
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