I solved the issue and this is how.
After lot of research and dozens of suggestions I decided to try something simple first.
My Samsung UE39F5500 was connected directly to the Internet, no cables apart from the power.
I opened the back of the TV and made sure everything was properly connected especially the highlighted part on the image. (shows how technical I am).
Thanks for your post re this dark band issue. You said "made sure everything was properly connected" but not that you found that a connection was lose or disconnected. Was there a lose connection? I had the same issue with my Samsung T27H390 It cleared it's self yesterday just by switching off and on again but today that didn't work. I read something about disconnecting hdmi cables and separate devices but the only connections mine has is LV power and terrestrial ariel so I pulled them out and plugged them back in and the dark band was gone. Hopefully this sorts the problem long term or at least doesn't have to be repeated too often.
any response to your post? I am having the same issue. It happened for the first time just a couple weeks ago and I had to do a manual software update but the same problem is back. dark screen on top of the picture, not software update available online.
my TV still works perfectly well after my expert (not) work on it.
from what i gathered from reading about the issue and watching lot of people offering solutions, the TV sometomes just needs "shaking" (not literal) and some TLC.
before buying anything or taking it to someone and pay for the repears, just have a go yourself.
i was very nervous opening its guts, but i had to try it.
not that i found anything loose, even if it was, there was no obvious way of spotting it. I just opened anything that can be opened and re-fix it again exactly how ot was, just made sure it was properly tight.
especially the area at the bottom (see image in previous post). tat is the part that most people suggest to replace. i didn't.
let me know what happened ...
please read the response i just gave to Salz51
there was nothing obviously loose, it would have been hard to spot anyway. but i still opened everything (almost everything) and re-connected it and made sure they are tight.
i am no expert but as they say "I did it my was".
i don't think it is HDMI issue.
good luck, let me know if it worked