Replaced PS Board In Revisited Samsung LED TV Model LA32D451G3
Those of you who have not read my earlier article may kindly do so as I will be focusing only on the problem reported this time and rectification done.
This TV which was attended to in March, 2023 returned in June, 2023 after a gap of only three months. This time the complaint was intermittent on/off and later fully dead. The customer also told me that there was loose contact in the non-standard type three pin plugs, as it was inserted with an adaptor which tends to get loose after sometime because of poor quality.
The Mosfets were found shorted along with SMD components on the LCD driver side and my attempts to revive it by replacing defective components were futile, by which time, the tracks were all in bad condition. After frequent consultations with my techie friends, I opened the back light case and looked for any dark contacts in the LCD holders or dark marks on the LCDs. I could not find any and everything looked quite clean:
I looked for any defective components in the driver board and checked the transformers for any shorts too. I could not find any. I tried using an LCD Driver that I had but did not succeed as it was not having enough power to drive the 32” type load. The external driver was connected to the contact ends for which, I had removed the transformers from the original driver board, to isolate the high voltage output.
The required driver was not available in the market. Hence, the final decision was taken to replace the PS board. When I posted the model and picture in the salvaged working board Whatsup group, I got a response from one in Gujarat and I verified the credentials through my contacts there and found it to be reliable. I placed the order not only for the PS Board but the LCD driver board as well, to avoid a possible mismatch.
We cannot take the risk of burning the LCDs due to some mistake, which then would call for entire backlight replacement with LED type, increasing the repair cost to beyond customer’s budget for this very old TV.
I got the board, which was equivalent, but with slightly different voltage outputs. I wanted BN44-0438A, but got BN44-0438B, in which the Driver Mosfets were not SMD type and were fixed on the top side. The output had one point for providing supply to Audio IC. The LED driver side was however ok. So, I had to remove the pins from the connector and re-insert them in the place where it was required to match the input to mother board.
As you can see from above two pictures, the original board had no 18V outputs, but the replacement received had 18V at pins 5 & 7. That’s why I had to remove these two pins from its sockets. Rest everything was in perfect place. Then I removed the driver board and fixed the replacement received and connected the PS Board to it and applied power. I was glad to see that the backlight was getting on without connecting it to mother board, which was typical to Samsung.
Then switched off power, waited until the developed voltages were drained and then connected the PS to the mother board. When I applied power, the TV was found working very well. I replaced the three pin power plug as desired by the customer to avoid loose contacts in future. I tested the TV for three days before giving delivery to customer. Mission accomplished with satisfaction getting added to collection!
This article was prepared for you by Parasuraman Subramanian from India. He is 74 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.
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You may check on his previous article on Crystal Oscillator Found Defective In LLOYD Air Conditioner Remote Control