It sounds like you’ve damaged the LCD chip when repairing the screen, the fact that you can’t see the display even in bright light such as a flashlight eradicates the backlight filter out of the problem. I’d say you’ve accidentally damaged the LCD chip on the logic board when replacing the screen.
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Also, check all connections from the flex cable to the LCD are tight.
Unfortunately, you’d have to replace the logic board to replace the LCD Chip.
It sounds like you’ve damaged the LCD chip when repairing the screen, the fact that you can’t see the display even in bright light such as a flashlight eradicates the backlight filter out of the problem. I’d say you’ve accidentally damaged the LCD chip on the logic board when replacing the screen.
Unfortunately, you’d have to replace the logic board to replace the LCD Chip.
Hope I could solve your problem.