Total Loss of Power Inside The House Due To Shorted Microwave Oven
As I entered my parent’s house, my mother approached me with a situation that happened inside the house just a day earlier. As she was using the microwave oven to heat up something, the earth leakage button in the main electrical board was tripped causing total loss of power inside the house.
I bought her this microwave oven about 12 years ago and this is the first time that caused such a problem. My brother was nearby and he was able to help. He unplugged the microwave oven from the main power line and then pushed up the earth leakage button in the main power board and the power was restored.
I took the cover off and this was the first thing that I saw.
It was dirty but keep in mind that this device was not opened for the past 12 years or maybe more.
The first thing to do was to discharge the main capacitor with a two screw drivers. This is a safety steps that has to be done before doing any kind of work on such devices.
To my surprise, the main fuse was not open when I tested it. In fact, when I powered the device in my shop, it was working fine and did not cause any problem. Usually when I encounter such a problem and the fuse was blown, I usually test the magnetron, the safety locks or the main transformer.
To be on the safe side, I preformed the ohm test on the magnetron, tested the safety lock and the logically the main transformer was ok since it powers up fine.
That is the main capacitor that has to be discharged before any repair done on this device. Next to that capacitor is the main bleeder which looks like a diode. Both checked to be working fine and in perfect conditions.
I noticed that the light of the microwave oven was off. I took the light bulb out and guess what? It was open. I have seen it happen before. When the cooking cycle starts in the microwave oven and the light bulb get open, it can cause the main power earth leakage to trip.
As you can see, when I tested the light bulb inside the microwave, it tested open. I did not replace it with another one, because I did not have any at the moment in my shop.
I took it back to my parent’s house and I told her the microwave oven is working fine but there is no light bulb inside. She smiled and said it is ok, do not worry about it.
This was a special mission accomplished for my precious mom. She was happy and I was happy that she was happy. Mission Accomplished.
This article was prepared for you by Waleed Rishmawi, one of our ‘Master Authors’ and currently working in the Bethlehem area of Palestine repairing electrical and electronic equipment.
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Jestine Yong works as an Electronics Repair Lecturer in Kuala Lumpur Malaysia and his training website is http://www.NoahtechElectronicsTraining.com. You can check out his repair blog at http://www.JestineYong.com
8 comments on “Total Loss of Power Inside The House Due To Shorted Microwave Oven”
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Odd that an open light bulb caused the tripping of the earth leakage button. Which is not connected to earth at all. Which could have something to do with leakage caused by building up moisture because of the failing light bulb while the Microwave Oven is active? But it also could be caused by incidentally shorting HV capacitor or other HV parts. Or it is an old earth leakage switch that has become too sensitive? Time will tell I guess?
Albert: the light bulb is not connected to ground and the actual Microwave oven is. I have seen it so many times. when the light bulb get open and it sparks, it can cause the earth leakage to trip. so far, it is working fine and I am happy for that.
Understood Waleed, good to know! I never had a bad Microwave light bulb before. It is the first time I heard about this to happen.
Sir,
Could you kindly offer an explanation for this: “When the cooking cycle starts in the microwave oven and the light bulb get open, it can cause the main power earth leakage to trip.”
Seems to me that the event causes a current/voltage surge, but I do not understand why.
Chad: yes, when the cooking cycle starts, the light get open caused by spark in the actual light caused the earth leakage to trip. I have seen it so many times.
I also didn´t understand. I don´t see how an open lamp could cause the GFCI to trip. Nothing to do with.
Henrique: when I opened the set, the light bulb measured open and that did not cause the earth leakage to trip, what caused the problem was the spark that caused the light bulb to go open is what tripped the earth leakage.
Waleed;
In the next to last photo, It seems to me that the “main bleeder” resistor is actually the HV diode. In most Microwaves – Isn’t the “bleeder” for cap inside the capacitor? The capacitor should have a little paper label stuck to it, showing the capacity / voltage ratings and the internal parallel connection of the internal bleeder resistor across the terminals.
Kyle