Microwave oven circuit breaker trip fix

by Updated: Mar 18, 2021diy-miscellaneous0 comments

Microwave oven circuit breaker trip fix

How to fix and repair by Avi

The problem:

Whenever the microwave’s door opens, no matter if it is working or not, it trips the circuit breaker of the house.

Some will tell you to replace the oven and buy a new one. This is really not necessary. You can easily fix it, save a lot of money, avoid trashing it and keep our planet cleaner.

DISCLAIMER – Important!

The fix:

exclaim2  For any repair you make, first disconnect the oven’s power cord from the mains.

1. Remove the oven’s hood, usually by removing some screws on hood’s sides and/or rear side.

2. First step is to make sure it is not a fuse issue.
Check if the fuse is burnt, if it is, replaces it with a ceramic slow-blow fuse. Mine was 10A 250V and you should verify its value by looking at what is written on it or by checking the oven’s manual.

If this didn’t solve the issue and it keeps tripping the circuit breaker, this is probably a malfunction of one of the door’s interlock switches.

Microwave ovens usually have a safety mechanism called ‘interlock’ that uses three switches (micro-switches) to disable its operation when the door is open. One or more of the switches are probably faulty and needs to be replaced, OR the door is misaligned due to excessive force applied to it.

3. While not connected to mains, check the door alignment. If it looks OK in both open and close position, go further and disassemble the three micro-switches that are located where the door’s latches enters the interlock mechanism.
Be careful while disassemble the switches as most manufacturers use plastic pins and snaps to hold the micro-switch in its place and you don’t want to break or bend it.

thumbUP_gifanim Tip: make a note or take a photo of the wires going to each switch.

Door lower latch two micro-switches
Schematic drawing of the three interlock switches
LG Latches and micro-switches layout

4. Test the switches with a multimeter. Pay attention to the switch type, usually one is N.C. and the other are N.O.
Review part 6 below for the test procedure.
If all three switches were found to be OK, then jump to part 10.

5. If found faulty, replace the faulty switch, or better, replace all three as it is not expensive.

My LG microwave oven uses the following micro switches:
SZM-V16-FA-61 N.C.
SZM-V16-FA-63 N.O. x2

exclaim2  Note: The micro-switch/s part number might be different in your oven. Check the parts you disassemble and consult with the oven’s service manual.  

Replacement micro-switches

6. BEFORE you assemble the switches, test it for continuity.
In my oven, the following test procedure was used:

Micro-switches test procedure

7. If the test was OK, assemble the switches to its place on the latch board and connect the wires to the switches.

8. Assemble the hood.

9. Connect the power cord to mains and open the door to test.
If all works OK, turn on the oven and try to open the door while it works. If all is OK, you succeeded in fixing this issue.

10. If it still trips the circuit breaker, further investigation is needed.
Possible causes might be the microwave’s cooling fan that might have failed or a short in the controller or in the line cord that feeds power to the oven.

This post does not cover those instances.
Most of the times that a circuit breaker trips while opening a microwave oven’s door is caused by a faulty micro-switch.

Voilà,
A simple and very low cost fix which will allow your microwave oven to work properly for years to come.

Enjoy your oven,
Avi clapup_gifanim

For more How-To guides by Avi, Visit the main DIY page

You might find there useful guides such as :

Panasonic PNLC-1029 charging cradle repair
Westinghouse ceiling fan fix and upgrade
How to repair LG refrigerator water leakage?

and more…

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Disclaimer

1. This product contains electronics and/or electric parts.

Any modification made to your product may cause damage to your equipment and harm to yourself or to others. 
Any modification made to your product AND/OR to a 3rd party attached accessories will void manufacturer warranty.
None of the following steps is recommended by me nor by the manufacturer. 
This post show only my personal experience and know-how.
If you follow any of the steps, you do it on your own risk and responsibility.

2. Copyright © 2003 Avi. All rights reserved. 

Content including all text and images in part or in whole may not be reproduced, retransmitted, stored, distributed, disseminated, sold, published, broadcast or circulated in any medium
without written consent of the author

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