Top half of screen is dark

Hi Mark, I have a Samsung UE50JU6800 that has just developed the same issue.

Whilst i dont have a definitive answer yet, i found a video from Shivamm Rane on youtube ( a search on Youtube will find it, unsure of iFixits rules on links ) that details replacing either the entire LED light strips or individual LEDs on Samsung TV’s that cause this issue. It will be a few weeks before i attempt my repair but hope this helps you on your way.

The replacement LED strips seems quite readily available on Ebay.

If i am successful in my repair will post a guide.