How to Repair a Microwave Oven

My microwave oven stopped working. If throw it away, the world will have one more trash and I will have to spend some more money to bring back a new one. I decided to open the microwave oven to see if I can save it.

The following steps are what I did. Finally, I fixed it and the cost is only $3.50.

Warning: 1) Read and Follow the warning label on the microwave oven. 2) Never open back cover on power plug in. 3) Capacitor must be discharged before beginning any repair (In my case, the step is not include, see step 8).

Step 1: Unplug Power and Remove Moving Parts

Be sure the power cord is unplugged and then remove the moving parts from microwave oven.

Step 2: Open the Back Cover

There are 2 screws on right side and 1 screw on left side. They can be easily remove with normal screwdriver. But there are 4 screws on the back are little special, a star screwdriver is needed.

Step 3: Check the Fuse First

After open the back cover, check the fuse first. I checked it with a resistor tester, if it shows the fuse resistance value is infinity. That means the fuse is broken. Only need to change a fuse for the microwave oven. But it showed a resistance value on the meter, this means the fuse is not broken. I have to go to find problem in some other places.

Step 4: Inspect Door Switches

The next step is to inspect door switches. There are 3 switches in the microwave oven. See their location in the pictures. Press down the pin beside the switch and rotate the switch a little to take it out. Inspect one by one, I found one switch is little different with others, the first is press the button there is no contacts click voice, the second, found there is something burned on the plastic by visual inspection.

Step 5: See Inside of the Switch

Open this switch to verify. In the picture, press the button down, the contacts cannot be connected. Yes, this one is broken. Since some plastic is burned, this switch has to be changed.

Step 6: Buy a Replacement Part

Found the spec and model on the back of the switch, I bought a similar switch online - the grey one on the picture, to replace the broken switch. Its cost is $3.50.

Step 7: Install the New Switch

The following things are connect wires to the new switch and install it properly. Just reverse the operation what I did. Close the back cover, drive in all screws and put the moving parts back.

Plug in power to test, the microwave oven works very well.

Step 8: About Discharge Capacitor

In my case, since the microwave oven has stopped working and unplugged power for a long time and there is one discharge resistor in the circuit, so I didn't show the discharge steps. I agree with the comments of instructablers. The capacitor must be discharged before beginning any repair.

The capacitor is in the back side lower corner. In my oven, it is covered by a plastic sheet. Please check it online how to discharge a capacitor.

Comments

[boitu.anna8]

Where can I get fuse

[DanielM19]

check at hardware and electronics shops or with your dealer ie where you bought the item

[mrstan]

Check with mouser.com or any electronics suppliers.. fuses are everywhere.. just be sure you get the right one with the right value and properties..

[DanielM19]

I have 2 national microwave ovens with same problem. The start button stopped working. All are digital. What could be the problem?
I also have a LG microwave smart inverter.... it stopped heating but everything else is as was.

[vitalispascal]

I am a technician. I have ramtons microwave oven model RM 236. The plate is rotating non stop. Unless I switch off from the main socket. Every button on the control panel is of except the start button. But nothing heating. Please help

[LindaJ148]

Can I get my Smeg Microwave fixed

[som162]

I have a 10 year LG Intellocook micro oven which gives kind of alarm like sound when switched on.I f the electrical cord is lifted at some angle the sound stops. The technician who attended says the fan has to be replaced, but I dont believe it. Please let me know if that could be the problem. Otherwise the oven works well.

[mreddyzn]

Good day please help I have a Samsung MS123HCE when microwave is plugged on it says sec and the microwave goes on it's own the button pad is not working properly.

[stephenbaa09]

i can not find switch please help me

[godwinbanda67]

My microwave is goes on nicely but if l start it to run then it start a flam on the side of transformer and it blows the main fuse some time pliz help

[Klind]

The glass tray is not rotating. I have recently replaced the rotation
motor three times with original new motor. It rotates when tested, but
after very minimal use stops working. For example, I replaced it last
night and it was working on a couple short few second tests. This
morning again not working. What should I be looking at and how to fix
it.

[pradeepvyair]

Glass tray start moving as door open of my LG Microwave oven.

[mrstan]

Great Instructable! Its a good one to refer to and informative...
The things I have seen in a microwave not working are the high voltage diode shorted or opened, and the 12v relay on the control board which drive the voltage on the magnetron. I think I have never seen a door switch broken unless someone physically damages them. NEVER EVER run a microwave with the door open, as RADAR EMF is coming out at a high Amount and will fry you or your electronics in its path... The door window has a grid with little holes... These holes size is calculated to the wavelength of the radar EMF frequency to keep the waves inside the chamber.
You can test the magnetron with an ohm meter, and the diode with a diode checker (higher current ohm meter).
Proper troubleshooting makes all the difference, or you are just shooting in the dark. When you run the unit, if you do not hear the "hum" sound but lights and table rotate, the magnetron is not activating which leads to the relay on the control board.. If it does hum, but does not heat very well or at all, the diode is faulty. If there is NO power (dead microwave), the fuse is most likely popped by surges or shorted capacitor.

[wflrich]

mrstan, I need your advice. I have a GE JE1860SB microwave. When it first stopped working, the power was totally gone. I get its power back on by replacing the "flame sensor" which GE named. It basically the thermo cut-off sensor. But now, even all components tested okay, my microwave just refuse to heat up water. I used 9v battery testing method with cheapy multimeter, and a Fluke 87V to test the HV diode. Both methods show the diode is okay. I tested the capacitor, reading 1.06 uF on a 1.05 uF rating. Resistant tests on transformer leads show no issue. All three door switches work, and transformer input end gets 110v. Resistant tests on magnetron is okay: almost 0 ohm between terminals, and each terminal to case is infinity resistant. While it doesn't even warm up a cup of water, the magnetron is warm to touch after the cooking cycle. I double checked power level setting, it is level 10.
Please help.

[mrstan]

I found the part numbers that you can use.. Magnetron is WB27X10939. I see it for sale on Amazon here:
https://www.amazon.com/GE-WB27X10939-Magnetron-Assembly-Microwave/dp/B004H3XQKM

Main board is AP2026210. I don't see it on sale anywhere though.
If it is the board, it will be the power relay on the board. Look at its part number and search for it..

[mrstan]

Hey there!
Have you checked on the relay that drives the magnetron? Different microwaves function differently as to the drive circuit, but if the main drive relay has popped a wire in it, it simply will not heat. Look on your main circuit board for a relay (looks like a square box with lots of connectors on the bottom side of the board it is mounted to (It might have the drive line on the top too). The relay basically is the "on/off" switch for the magnetron to deliver radar EMF.
when you run the microwave, you can tell it is working because you will see or hear what can be described as a "big hum" intermittently which is the magnetron cycling and shooting out the radar waves. If you don't hear this, your relay has popped. I attached a picture of a typical relay and a schematic of what is inside of it. See if you can see some of these on your circuit board. Again, it is basicly a controlled "on/off" switch to drive the magnetron circuit. I have had to replace this relay on various microwaves which are not "cooking". I am sure you have the same situation there.

[ahkha1345]

Hello, I removed cover of LG microwave MC-8044WR for replacing its lamp. Now, I do not know how to assemble parts of attached images.

[mrstan]

Hey!
Check this out. These guys sell parts for your microwave and this link shows the internal panels that might help you get it back in order.. Let me know if this helps you out. Buy something from these guys if it does. Its nice when these vendors have this information to help you out..

https://www.appliancepartspros.com/parts-for-frigi...

[marvinx97]

If the fuse is blown in a Microwave the chances are it is a more fundamental fault either a capacitor failure or the transformer or the magnetron. photo a blown mains transformer there are some very heavy induction loads in this type of circuitry so other than switch failure most of these faults are beyond economic repair a Magnetron $20+ a Transformer $40 even a thermal fuse $10. so unless you have dead units that can be cannibalised -just by a basic model for around $50.

[wflrich]

Totally agreed! Fuse is normally the last protection to prevent other damage. So, at least visual inspection on all components, before replace the fuse then power on.