How to Repair a Microwave Oven

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Introduction: 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).

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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.

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    30 Discussions

    0
    k3nlind
    k3nlind

    Question 3 months ago

    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.

    0
    pradeepvyair
    pradeepvyair

    4 months ago

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

    0
    mrstan
    mrstan

    8 months ago

    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.

    0
    wflrich
    wflrich

    Reply 6 months ago

    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.

    20191115_215215.jpg
    0
    mrstan
    mrstan

    Reply 6 months ago

    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.

    relay image.jpgRelay Schematic.png
    0
    ahkha1345
    ahkha1345

    8 months ago

    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.

    20190910_175507.jpg20190910_175535.jpg
    0
    mrstan
    mrstan

    Reply 6 months ago

    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...

    0
    marvinx97
    marvinx97

    4 years ago

    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.

    MOTremovedsec.jpg
    0
    wflrich
    wflrich

    Reply 6 months ago

    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.

    0
    Hammerhead46
    Hammerhead46

    Reply 3 years ago

    9 times out of 10 if the fuse is blown one of the door switches is defective!

    IF one is defective replace all 3 as the one that is defective is normally the "Safety" Switch which SHORTS across the AC line if one of the other (2) TWO switches does not open at the correct time as the door opens with the microwave operating.

    This is from repairing microwave ovens for 25 + years.

    0
    mariyame
    mariyame

    7 months ago

    We have a microwave oven/hood. It’s a Kenmore Elite.. it worked all fine then it started having the issue that when you close the door, the light would still be on as if the door isn’t closed all the way so we had to reclose it a little harder. Then it got to the point that when you press start to heat things up, it would still light up and the table is turning but no sound or heat comes out. Sometimes we would get the error code F5

    Anyone know what could be wrong?

    My last one quit working while letting the magic blue smoke out and needed to be hit with a fire extinguisher. I don't think it was worth trying to save. I will keep this bookmarked for more normal failures. Btw the power supply and all had fire ants in it. Oh the joys of living in the Southern US

    0
    mrstan
    mrstan

    Reply 8 months ago

    Interesting comment.. The University of Alabama did a test and found fire ants are attracted to the electronic hum of transformers like on power polls. Whether it is the sound of the hum, or the EMF emissions they detect, is what they are investigating.
    I have been watching this research because I have a power transformer box in my front yard for my neighborhood and have noticed it regularly gets invaded with fire ants in the warm months. Its funny to watch the power guys go running away after being stung a few times. LOL

    0
    abumajd101975
    abumajd101975

    Question 2 years ago

    how i can discharge the capacitors

    0
    mrstan
    mrstan

    Answer 8 months ago

    short the two pins together. I use two insulated screwdrivers touching... just dont touch the mettal parts.

    0
    PrinceM52
    PrinceM52

    Question 1 year ago on Introduction

    MAIN SUPLY FUSE BLOWN AFTER 3 DAYS USES.....
    ALL FUNCTION WORK PROPERLY....

    PLZ HELP ME FOR SOLVE THE PROBLEM.

    0
    mrstan
    mrstan

    Answer 8 months ago

    check the big capacitor.. it sounds like it is shorting out or is drying up inside.. This will make the short to ground internally and pop the fuse. See if that helps.

    0
    TatianaC17
    TatianaC17

    Question 1 year ago

    This sentence does not quite make sense.

    "Never open back cover on power plug in."

    Tatiana Covington

    0
    mrstan
    mrstan

    Answer 8 months ago

    are you making a grammar police arrest? It makes perfect sense.. just grammar was off. "Do not open the back with it plugged in". Is that better?