I purchased a UN65KS9800 in 2016 and just last week my screen went dark. Everything seemed to work. The volume still worked, and I could hear the Smart Hub pop up when I hit the button. I tried to call Samsung support and they told me it would have to be serviced. They also let me know that it was no longer under warranty and it would be at my cost. I wasn't happy, but I was fine with that. He looked up my location and told me that they didn't have anybody to service it in my area which is Northwest Indiana. Basically I was on my own to find a place to repair this TV. I decided to do a little research and found out this is happening quite often on these Samsung TV's. It usually occurs around 3 years old. Did I mentinon this TV cost several thousand dollars. This was the flagship of the Samsung fleet, and is the full backlit array (QLED) series that they still sell today. I took it to a repair shop that used to be a Samsung certified repair shop. He is still looking into it, but believes it's the screen that actually failed. I am now stuck with looking for a new TV if this is truely the case. I really enjoyed everything about my Samsung TV, but am now uncertain that I will ever own one again. I have had zero help from Samsung on this issue even though I'm willing to pay since it's not under warranty. It sounds like this is a known issue on Samsung's part but they are not willing to step up and help a loyal Samsung customer out.
Did you ever figure out what caused this? I am having the same issue myself. I can hear sound and the screen seems to be dark with sporadic light shadows in the background. After doing some research on YouTube, I was certain it was the TCON board.. so decided to purchase a bunch of parts from EBay .. tcon board , led driver board, power board and hdmi board.. basically every component visible when you take the back off. Unfortunately.. changing everything out.. nothing worked .. seems like this issue is with the Internal screen panel.. there is no way I can get in there without a pro and probably expensive. It's sad I purchase their 2016 flagship and a little over 4 years this went bad. I am really curious what is the issue with the un65ks9800 model. Samsung needs to do something about this. Why is this failing 4 years later. I went out and got your 65ts900 .. I really do hope this don't fail in 4 years .