Hi @theotheroracle ,
Things to try to resolve the problem:
i). Check if the display stays on when the phone is in recovery mode
If it does then try wiping the cache partition and then check if it stays on.
To do this, enter recovery mode as shown above and the scroll down to wipe cache partition using the Volume buttons and then select it by pressing the Power button and then follow the prompts.
ii). Try starting the phone in safe mode and check if it works OK.
If it does then a downloaded app is the cause of the problem. You will need to uninstall each downloaded app, one by one and test the phone in normal mode between each uninstall to see if it now works OK. When it does then the last downloaded app that was uninstalled was the problem. A downloaded app was one that you downloaded and installed on the phone and wasn’t already pre-installed when you got it.
iii). With the phone turned on try shining a torch at an angle close to the screen and check if you can see any images at all. They will be very faint if they are there, so trying this in a darkened room may help to see them.
If you can see images then there is a backlight problem (or even if you can’t but at least you know what it might be if you can see images) then the problem could either be in the systemboard or the display. As a DIY repair all you can try is to replace the display and check. If the new replacement is also faulty then the problem is on the systemboard.
Was the battery disconnected from the systemboard when the display was replaced? I don’t know the phone but with some mobile phones there is a backlight power fuse mounted on the systemboard close to the display flex cable connector on the board. It may be worthwhile checking to see if it is OK or not if there is also one in your phone, that is.