How To Repair Samsung LCD TV With Vertical Lines
I received this defective Samsung model: LA40A650AIRXX which has vertical lines superimposed on to the video signal. The intensity of the vertical lines changes with the RGB signals and very prominent on white video signal as shown below:
Since the vertical lines are not in the static location and always changing with the video display so, it is unlikely the LCD panel is at fault. The possible cause could be the main board, T-con board or both. I performed a grey scale test with the same procedure as in my earlier article on gamma distortion.
There is no gamma distortion or noise on the grey scale but RGB vertical lines are being superimposed on it (see photo 1). The intensity of the vertical lines changes with the contrast level as well.
I suspected the gamma IC is faulty although it displayed no gamma distortion. The gamma IC on the T-con board is IC18 with part no. ISL24005. After changing the this IC there is a remarkable improvement on the video quality except for some fine vertical lines still visible only at high contrast level. As I have suspected earlier the main board is also contributing to the problem. Changing the main board will be ideal but may not be worthwhile as the main board is not cheap. By reducing the sub-contrast level and the RGB gain by a certain value in the service mode, the vertical lines are not visible and the reduction in gain and contrast level have not change the video quality significantly as shown below. The customer is very happy and satisfied with the end result as the repair cost does not burnt a hole in his pocket.
Tips: Reworking manually on IC18 is not an easy task due to the QFP packaging being small, thin and leadless. The back of the IC is soldered to the board as well which make it more difficult to remove . After carefully removed the IC without damaging the board, I have a hard time trying to re-align the position of the new IC as the solder pads are underneath and difficult to view from the edges. After a few soldering attempts I managed to re-soldered it.
This article was prepared for you by SK Wong from Malaysia and he graduated from London with a degree in Electronics and Electrical Engineering. He has more than 40 years of experience in the consumer product manufacturing. With the passion to repair electronic products from young , he has been doing it part time until now.
Currently, he can provide turnkey solutions for consumer products including services from idea or concept to design , prototyping , finished products (including electronic,mechanical and plastic parts) and manufacturing.
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Note: You can check his previous repair articles below: