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jimmy12345678  
#1 Posted : Tuesday, June 27, 2017 8:54:42 AM(UTC)
jimmy12345678

Rank: Member

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Joined: 6/27/2017(UTC)
Posts: 3

The other day I went to heat up food in my Kenmore microwave and after about 15-20 seconds there was smoke rolling out of it. So I unplugged it and took the cover over to see what was wrong. I ran it with the cover off and noticed that the transformer was getting very hot and that's what was smoking, so I found another one that would fit and installed it. Now the microwave turns on and doesn't smoke, but it also doesn't make things hot. I put a cup of water in there for a minute and it was still ice cold.

I've searched online and found Microtech Factory Service Microtech Factory Service. Expert microwave oven repair for the Florida-Alabama Gulf Coast and they had diagnostic procedures to test the various components inside a microwave. I'll post the results of those tests below:

Transformer

Between Primary Windings - 0.2 ohms (Old and New)
Between Primary Leads And Ground - Open
Between Filiment Wires - 0.2 ohms (Old and New)
Between Filiment Leads And Ground - Open (Old and New)
Between Voltage Tap and ground - Old One - 848 ohms (spec says 55-70 Ohms) [COLOR="DarkRed"]New One - 102 Ohms[/COLOR] I don't know if this is too far out of spec or not

Magnetron:

Between Both Terminals - 0.2 Ohms
Between Terminals And Ground - Open

Capacitor:

Between both terminals - Slowly climbs to OL, when switched goes back to zero and starts climbing back to OL
Between terminals and ground - Open

Diode:
0.2M Ohms one way
OL other way


Thermal Protectors (2)

Both 0.2 ohms across terminals


It just doesn't make any sense why it doesn't work now. It worked on Saturday, then yesterday I used it and that's when the transformer overheated. And I didn't touch anything else inside, just wired up the new transformer just as the old one was. Same specs on both of them (120v, 60 Hz). Unless this new transformer is also defective (as I said, the 102 Ohms on the high side is above the spec I found).

If anyone can help me or they need me to conduct more tests I'm more than happy to help. Thanks!!!
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jimmy12345678  
#2 Posted : Monday, July 3, 2017 11:29:13 AM(UTC)
jimmy12345678

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Joined: 6/27/2017(UTC)
Posts: 3

I never received a reply on here but I'll go ahead and update you guys so that anybody else having this problem can figure it out too.

Here are some of the replies I received on 3 other appliance repair forums:

Originally Posted by: jeff1 Go to Quoted Post
Hi,

A copy:

Q - Hello, My Microwave Oven is about 5 years old and won't heat food anymore. Any hints on what electrical circuits to check?

A - Confirm 110-120 volts AC is entering the primary coil on the high voltage transformer....meter works but can be fooled, I usually rig up a light socket and household light bulb and hook that to the 2 input wires for the transformer and see if the light works or not when you run the microwave....can even set a power level and watch the light go on and off. Discharge the capacitor first before attempting any checks or tests.

Scary but works!....

If ok, put those 2 wires back on the transformer. Discharge the capacitor.

Remove the 2 wires going to the magnetron....run the microwave a few seconds ( 2-3 ) and remove power....again discharge the high voltage capacitor. If you got a good crack & spark when you discharge the cap the second time you are creating high voltage but not using it ( bad magnetron or loose High Voltage wire somewhere )....if you get no crack & spark you are not creating high voltage. This will work on all microwaves with a transformer and diode system ( not the inverter style ).

jeff.



I did was was mentioned above and found that the new transformer was creating high voltage, but the magnetron was not using it so therefore the magnetron is bad.

I searched the part number off the old magnetron on ******** and found an exact match for $35, so I ordered it and installed it today when it showed up in the mail. It is now making heat as it should.

I had a lot of fun learning how microwaves work and how to diagnose common problems with them! Hope somebody finds this information helpful!
twin cam  
#3 Posted : Sunday, August 6, 2017 11:38:50 AM(UTC)
twin cam

Rank: Member

Groups: Registered
Joined: 8/6/2017(UTC)
Posts: 1

This is a wonderful microwave that sits up under my counter. Last week it made a loud humming noise so we open the door and stopped it. Then it wouldn't turn on anymore. Can I fix this by myself? If so, how?
sandy webb  
#4 Posted : Thursday, September 14, 2017 9:31:42 AM(UTC)
sandy webb

Rank: Member

Groups: Registered
Joined: 9/14/2017(UTC)
Posts: 1

It worked last night and made all the right moves this morning but no heat.
Normally I can hear the magnetron cycling as the fan and table turn.
This unit has been excellent for 15 years but my wife won't wait for a fix.
I have plumbing, roofing and travelling I have to do. I will save the unit for my hangar and let you know how repairs progress. Jimmy 12345678 has been a lot of encouragement and deserves at least a nod. More later.
Sandy Webb
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