How To Repair No Power Symptom In LED TV
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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Note: You may check out his previous post in the below links:
https://jestineyong.com/burnt-coil-in-fan-motor-winding/
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Parasuraman
February 19, 2018 at 2:21 pm
As usual a fool proof troubleshooting! Good job!
Albert van Bemmelen
February 19, 2018 at 4:57 pm
Indeed a quite straight forward repair solution! Always interesting to know what caused this. Probably the shorting diodes and defect power Fet were caused by a power mains lightning strike? or if the Fet caused this after it was shorting the input current, it also would explain the shorting diodes and blown fuse.
Joshua oloo
February 19, 2018 at 7:29 pm
Thanks for the Article.
Andrew F. Ali
February 19, 2018 at 8:52 pm
Nice repair. Sometimes the PWM IC also goes bad when the FET goes short cct. Good work.
Thierry Rouviere
February 20, 2018 at 3:08 am
Bravo et merci
============
Congratulations and thank you
Humberto
February 21, 2018 at 3:25 am
Hi Suranga, nice repair. But I think like Albert, what caused that short?
Moniem
February 21, 2018 at 9:55 pm
Good job
Amir Mukhtar Ashrafi
February 23, 2018 at 12:27 pm
thank you Mr. Suranga Bandara for Sharing such a nice Expertise article.
you are doing best and share knowledge to Learn beginners and Students Like me.
Thanks you Again.
Keep Sharing.
Amir Mukhtar AShrafi
A Student of Electronics
karachi. PK.
Yogesh Panchal
February 26, 2018 at 1:50 am
Suranga, Good Job!
Akbar Hazara
February 28, 2018 at 2:13 am
This sort of damage might have been caused by bad weather and lightning. The best way to avoid this, in my opinion, is to use a voltage guard such as a voltage stabilizer in between the tv power cord and mains socket,
angelo
March 8, 2018 at 2:49 am
I noticed that u used a 40w bulb
can I use it with a 21" CRT color tv?
thank u sir
Patrick
April 15, 2018 at 1:36 am
Very simple and educative article. Thanks for sharing I have really learnt alot