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).

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

author
marvinx97 (author)2016-04-26

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.

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author
Hammerhead46 (author)marvinx972016-08-06

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.

author
texdanl (author)2016-04-25

After you are done make a simple tester. Get 3 or 4 little neon lights trim off the wires leaving only a couple of half inch wires. Take a 4" by 1" piece of cardboard and poke little holes, 2 each, for each light. Poke the wires through the cardboard, stick the wires through the holes and then bend the wires flat on the bottom of the little piece of cardboard. Set it on top of a cup full of water and turn the microwave on. As the magnetron is powered up the lights will flash. The different power settings are simply based of the percentage of time that the power is sent to the magnetron. You need to check this to make sure that this circut is working correctly.

author

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

author
BeachsideHank (author)2016-04-24

Door interlock safety switches are the number 1 problem when an oven fails to operate. Two of them are normally closed, one of them is normally open in their nature so like you found, a simple continuity test will reveal the malfunctioning one. Although ovens manufactured for the last 20 years have a discharge circuit designed to bleed off any high voltage left in the capacitor, still treat that area with respect and do some online research before opening a microwave oven. By the way, using a Dremel type tool, you can easily slot the special security screws found on the back flange of the case top and just use a plain flat screwdriver to unfasten them.

author
amjohnny (author)BeachsideHank2016-04-25

Thank you for your comment!

I agree discharge capacitor first. It is the right way. In my case, the oven has stopped working and unplugged for a long time so in the steps I didn't show discharge.

author
Jesper K.P (author)2016-04-25

Do not do this! a microwave oven can be a dangerous even lethal machine. if it does not work. have a professional look at it.

author
Markomyt1 (author)2016-04-24

Microwave ovens have a very powerful capacitor as part of their circuitry,

BE VERY CAREFUL!

This can kill you!

author
mkramer4 (author)2016-04-24

Great work. I teach my children this method as well. Everything can be repaired, we need to stop throwing away good products.