55 Inch Curved LED Samsung Television Model UA55MU7350K Came In Dead Now Repaired.
I received a phone call from a client who wanted his television checked by a technician, he requested for my ping location and I send him via whatsapp.
Within one hour he called me to say that he is around my area, I walked out and ushered him to the shop. I carried the 55-inch television into the shop and we had a small chat. I asked him how he came to know me and said he was referred to me by another client I repaired his television previously.
This info always put a smile on my face, a happy client will always come back and refer more client to your shop. After that little introduction, now it is time to do business and the business was to see his Television back to life.
I asked for a short history about the problem and he told me that they were just watching football and when his favorite team was about to score the television went down! He took it to the nearest technician and the technician told him the power board is faulty and beyond repair and hence needed a new power board.
He gave the technician the amount needed and the tech came back after two weeks with a board and installed it and nothing happens, still dead symptoms. The tech told him maybe the board is not compatible and left in hurry, the owner suspect the board was the same he took and even me I have no reason to doubt him since he was not given the other board, how sad?
Since the Television was brought in the evening I decided to check it out in the morning and therefore closed the shop.
Day two, I opened the television and went straight to main fuse and found it was open circuit. I replaced it with a jumper wire (this was done only for testing purposes) and applied the power via the series bulb current limiter and nothing happened. Noted no input at the AC connector and after testing the television power cable fuse (top plug) and was found open circuit also.
I replaced it and again applied the power and now I noted the series bulb current limiter was as bright as the sun.
Usually if you get this kind of scenario always expect a heavy short ahead. I checked the voltage across the main capacitor and got almost zero volts. I decided to dis-connect the power and do resistance testing looking for the shorted component(s).
I tested across the main capacitor and got a beep, this means there is a component shorted across the line. To isolate the problem, I decided to disconnect the transistors QP801 and QP802 guided by a circuit diagram I got from the net which was not exact but close to what I was looking for as you can below.
I did this by soldering out the two transistors(mosfets) as you can see below.
After soldering the two components out of the circuit, I applied the power again and the bulb went on briefly and off. With this I concluded no more shorted component and therefore I had to go to the shop to buy the two components which were both N-channel mosfet transistors, luckily they are readily in my market.
I came back with my parts and replaced them, applied the power again using the series bulb current limiter and power board was now powering on but power was pulsating. I decided to change the control I.C (ICM801S) which was driving these mosfets, the part number was 6C17106 which was an SMD I.C.
Getting an smd component is my local market is not easy and knew the road ahead will be bumpy. First I decided to check with my local technician to find out if they have the ic from their junk board, I got one and I bought it at 10 dollars (1000 kshs)
I went home happy and before replacing the I.C decided to confirm the part number only to find I was given the wrong part; the tech took advantage I did not have the magnifying lens to check the number. I decided not to go there again but import the part,I got it at aliexpress and within one month the item landed in Kenya.
I replaced the part and applied the power and was happy with the results. I put the power board back to the main television and after applying the power I noted the backlight were on from the back of the television since the television was placed upside down.
I checked the screen and noted it was indicating “no signal”. I re-assembled everything slowly and carefully and after connecting the antenna this is what I saw.
For more information on LCD/LED television troubleshooting and repair guide you can grab this eBook written from the technician workbench point of view.
Thank you friends
Humphrey Kimathi is from Nairobi Kenya and he has just launched his new book “Foundations Electricity & Electronics”
You can also checkout his other ebooks below:
3) CRT Television repair course and
4) Basic Electronics course.
He is also a blogger at Electronicsrepairmadeasy.com
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