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This Polytron LED TV came in with the complaint of no power. I retested the TV by connecting the AC input and yes indeed it was no power. After the removal of the TV cover I saw three circuit boards.
The circuit boards are the power supply board, main board and the T-con board-see the photo below:
Since the complaint was no power so the first thing to check was the main fuse. From visual inspection it was very clear that the main fuse was severely blown-see the white arrow in the photo below. This indicated a direct short circuit in component that had caused a large current drawn that had blown the fuse.
I proceeded to check on the bridge rectifier and found all the four diodes were shorted.
Next, I checked on the main power FET and it was shorted too- see the two photos below:
Further testing of components corresponding to the power FET did not yield any bad components. I then replaced the bad components with new one (except the main fuse) and soldered a light bulb across the fuse holder to check and make sure no more shorted components. The power LED lighted up and I knew now I can put in the main fuse and power On.
The result was a perfect picture -see the photo below:
Conclusion- It was a quite straight forward solution and if you would like to troubleshoot and repair power supplies like a professional I suggest that you check out Jestine Yong’s ebook HERE.
This article was prepared for you by Suranga Bandara who owns an Electronics repair shop in Anuradapura, Sri Lanka.
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