My iPhone 6 screen is super dark, you can only see it in pitch black after your eyes have adjusted?

So I got this iPhone 6 from my cousin, and I replaced the screen because it was shattered. It worked well for a while, and then after several months the screen went black. I noticed that I could barely see the screen in pitch black, so I replaced the screen again, and it didn't fix it. So I was wondering if anyone knows what the problem would be. Something wrong on the motherboard? Maybe a broken backlight chip? I just need to know what to fix so I can fix it and give it to a friend as a birthday gift.

Yes

Most likely the backlight driver circuit has blown could be a faulty diode or the driver chip. Unless you have access to schematics, replacement parts, a hot air station, and an operating microscope trying to fix it yourself is a non starter. Take it to a mobile/cell phone repair shop. If you take it to an Apple store they would simply sell you a refurbished iphone with 3m warranty

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