This microwave oven was brought to my shop for repair and the problem was, it does not heat up. While the customer awaits in my shop, I did a small test. I put some water inside the microwave oven and tried to see if it heats the water or not. When turning on the oven, I could hear a loud noise coming from inside the microwave oven and it did not heat up the water.
From experience, when the microwave oven does not heat up, there is three possibilities:
1- The 220 volts is not reaching the main power transformer
2- The magnetron is shorted out
3- The .70 amp/5000 volts fuse between the 220 volts power transformer and the main capacitor is open causing the magnetron not to work due to the absence of power there.
By testing, I could read 220 volts reaching the main power transformer. The magnetron is not shorted out; This testing is done by testing the ohm reading between the metal body of the magnetron and the two terminals of the magnetron. If you get any reading between the terminals and the magnetron metal body, it is shorted and needed to be replaced. Usually the two terminals are connected together from the inside. It you test these two terminals with a continuity test setting, you will hear a beep. That is very normal.
I checked the fuse that is connecting the transformer to the main capacitor and it was open. this is a common problem in microwaves oven to find an open fuse there. Many repair technicians replace the fuse with higher amp rating causing the magnetron to blown or shorted it on the long run. It is very important to replace it with the same fuse specification to avoid any kind of problem in the microwave oven.
I replaced the fuse and turned the machine on. It worked and the water I put in the microwave oven started to get hot. One more problem remained; that is the loud noise of the oven. It was not suppose to have this loud noise. Usually, this is a problem with the main capacitor in the microwave and I think that is the main reason why the fuse was blown in the first place.
It is a very easy process to replace the capacitors but it is very important to make sure that the old capacitor in the microwave oven is discharged before replacing it. Even if the capacitor is bad, just make sure, it was discharged before replacing it with a new one. Upon replacing the old capacitor with a new one, the noise was gone.
The microwave ovens are very easy to fix and it can generated good income if you know how to do it. Just be careful when dealing with capacitors and magnetrons. Enjoy your repair and be safe.


10 years of practical electronics. owner and operator. I service the Bethlehem area in Palestine. I repair Xbox 360 and all play stations and modify their power supplies. also repair lcd and Plasma tv sets, and lcd computer monitors. I have a degree from Bob Jones University in general business and one year degree in Industrial electronics. a intensive course in Media. I also work as a camera and audio man as a free lancer. Also great experience in video editing and installing surround systems for home and movie theaters.

One comment on “LG microwave oven that does not heat up. LG MS-204H

  1. Sanan says:

    Hi Waleed. Nice article! Very informative and a number of useful methods described in depth. It seems no one except you is going to make his contribution to this site as it was in the early stages of its creation. Could you please explain briefly short detection method described above. Should we use analog or digital multimeter for such purposes? One meter probe goes to metal body and the other one to one of the terminals separately or … and finally can we use this method generally in recpect to all metal body appliances? Thank you in advance!

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