Chosen Solution
My iPhone 8 plus’s screen randomly turns black, while using. It isn’t turning off but rather the screen just goes to a black color. While in this state I can still click things and was even able to swipe up and start playing music. I powered the phone down completely and powered it back up but the issue persists. I recorded time intervals it took to go to this and it varies dramatically. The lock screen will come on and stay on until it times out and other times only last milliseconds before going to this “black” but still turned on mode. Also my home button does not work but this is an unrelated issue ( the ribbon cable broke during a screen replacement about 7 months ago), but keep that in mind when a fix is suggested. —UPDATE: I have opened up the phone and check internal connections to the motherboard and everything is connected just fine. Then about an hour later the screen stopped producing the black screen and now produces no light at all. However, the touch pad still works (I can hear when a pass code is being typed in, but there screen appears to be off.)
Its most likely that the connector is incorrectly attached. There is a 99% chance of that being the issue. 1% chance that you have a bad part. It is most likely that you incorrectly plugged something in on the inside.
This might Be a mother board issue or connector as most people put on a different generation screen and then the mother board connector gets fried but you are still able to use the screen. Are you sure this is not a 7 plus screen?
First insure that the display connector is good.If you insert iPhone 7 LCD on 8 plus the maxium chances is that the connector might be loose that causes may that issues. If the connector is looking good in a condition check the Gnd resistance on LCD connector or might be the problem of Chestnut IC and light IC too.I also faced that same problem like you and i solved it by this ways replacing chestnut,and two light IC.
