What causes a wide horizontal faded area on tv screen?

@hamidmarko that is NOT a backlight issue, nor is it a T-con board or main board error. What you have here, is a failed/failing source driver. You need to dig deep into your TV. Check the "long, skinny" boards, that are attached to the display via some ribbon cables. Those DO NOT come off. Handle those boards carefully. Check the cable that enters the panel exactly where your defect is. Then apply some gentle pressure on it, to see if you can get it to make contact. Inspect the ribbon cable for any burns or even minute signs of burns or tears. You will have to do all of this while the TV is on, so be careful do not touch the power board. It'll bite :-)

If you need to find something, or get stuck, or need more of an explanation, post some good pictures of your boards etc. with your Question. That way we can see what you see.

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@tanveerzubair you do never change a display because of a bad backlight. We are not here to increase eWaste. We are here to avoid it.

A failed backlight will always be black, not translucent. It will not be in straight lines because of the way a backlight is made.

Don't just advise people to replace panels. Those are expensive and hard to come by. A lot of times they are not even available. Try to narrow it down to what may be causing it.