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Hello, Sorry you're having problems. A darker band on the screen would generally point to a failing section of LED's in the screen itself, which is not easily repairable. There are however light strips available if you want to replace that section of lighting in the screen. However what I would suggest first, is carefully removing and re-seating all of the connections to the power supply/LED board first (even if these were not touched) just to make sure that all connections are secure and attached tightly between the LED panel and the power board. If that is not the cure, then the LED strips for your screen can be purchased at the link below- but requires complete separation of the screen to access and replace the strips:
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