The owner of the microwave oven is a friend of my house friend. She bought a new microwave oven because her old one is broken. She said the display panel is working, but as soon as an ON button is pushed, the fuse/breaker in the basement is blown. She asked if I could fix it.
It is a GE model
(1550 W, very large size: 30x15.3x15.7 inch, 76x39x40 cm)
I checked on youtube, this GE model with this problem is not uncommon. It is usually a broken switch which causes the problem.
To find and fix the problem:
1. Unscrew 4 screws on top of the microwave oven:
For that screw on the bottom of 8 cm from the top, use a magnetic screw driver or just a regular screw driver:
2. Open the door, then move the panel A towards yourself (the green arrow) a little bit, you don't need to remove the panel, just move the right side one inch or so, so that you could work on B. Lift the panel B up (the green arrow) and take it off from the microwave oven enclosure:
you will get, with panel B still wired:
Panel B removed:
3. To remove the switch assembly from the microwave oven case, remove 3 screws (A is not shown, it should be in line with the other two scres):
4. Take the switch assembly off by moving the assembly upward (green arrows)
Now, the switch assembly is off:
It is tricky to take the bad switch off. To take the switch off, you have to use a sharp awl, to lift up a plastic off from the back of the switch assambly. Be carefiul not to break the plastic piece (I broke it and later using a glue gun to glue it). (Sorry. I did not take a picture).
5. Check 3 switches, by using a chop-stick to push the switch button, if you hear a clicking sound, the switch is good (in this case only), if you couldn't hear the sound, the switch is bad (in this case only) or you could take the female connectors off and measure with your multimeter with a sign
:
using a multimeter to check before the button is pushed and after:
6. One of 3 switches on the switch assembly did not response to the pushed button, that switch is bad. That is the middle one on the switch assembly.
The following picture is not from the switch assembly, just show that there are 3 types of switches. Order a switch form Amazon, there are 3 kinds of swiches with the same name.
a. NC: normal closed
b. NO: normal open
c. NO and NC:
They are all called KW3AT, some of them with KW3AT-16 (16 W).
The broken one is NC. I bought a switch with both NC and NO.
But the pins are wider, so I have to file them. The broken one:
the one I bought:
7. File them:
with either a file or A bit from a rotary tool:
from a rotary tool:
8. When the switch is installed, you could find the filed pins:
9. Reconnect wires for the front panel:
10. Installed all panels and screws:
11. The microwave oven is fixed:
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Why does the fuse/breaker keep blown:
https://www.tophomeapps.com/ge-microwave-fuse-keeps-blowing/
Door Switch Problem
A door switch probably has a problem when a fuse breaks while the door is being opened or closed.
Microwave ovens often contain three or four door switches that are intended to trip a fuse and turn off power to the microwave if the door is not closed correctly.
Usually, a door switch will stop working because of wear and tear or because it is jammed. The wrong door switches being placed might potentially blow a fuse.
Using a multimeter, door switches may be checked for continuity (a continuous electrical route) to see whether they need to be changed.
Before using the microwave, be sure to heed the safety advice above.
This switch is controlled by the door. When the door is open, this switch is closed (NC, normal closed). When the door is closed, where the button is pushed, this switch should be open.
But the broken switch does not fuction. Either the door open or closed, the switch remains closed. When the button is pushed (the door is closed), it remains closed.
So I think, this closed switch probably makes a short circuit when the ON button on the display panel is pushed (while the door is closed), the fuse/breaker in the basement keeps blown.
The new switch restore the original circuit, when the door is closed, it makes no short circuit, so the fuse/breaker will not be blown.
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