Mirroring 4K content using a cat 6 cable and a balun.

Are you set up in a "mirror" situation (same content on two screens) or just a single? That looks more like an extender.

What troubleshooting have you done?
Try with a short (ie: <10') network cable.
Try it with multiple HDMI sources (Receiver, Laptop, DVD player).

Once you get it to work with a certain source and a certain length cable, then change one OR the other, never both at the same time.
 
Dont you also need a HDMI splitter? One for the TV and another going to the extender?
 
I found the solution to the problem. And the answer is weird. Initially, I purchased a square cat 7 cable (75') and it didn't work. I read on Amazon it only works with a round cat 6 cable. And it does. I don't understand the difference but its working like a champ. A simple HDMI splitter doesn't work for more than 15' in 4K. That's why a balin was the best choice. It has a IR blaster so the remotes works on the 2nd TV location.
 
I found the solution to the problem. And the answer is weird. Initially, I purchased a square cat 7 cable (75') and it didn't work. I read on Amazon it only works with a round cat 6 cable. And it does. I don't understand the difference but its working like a champ. A simple HDMI splitter doesn't work for more than 15' in 4K. That's why a balin was the best choice. It has a IR blaster so the remotes works on the 2nd TV location.
A "square" cable? Network cable works by each pair being twisted a certain number of times, then the four pairs being twisted around them. Maybe over that distance the twisting wasn't right to support the signal.
 
Was it one of those cheapo flat cables that toute nonsense on Amazon? If that’s the case, it wasn’t truly Cat7. The Cat7 specification needs shielding and a drain wire in the cable, then even more shielding on each individual cable pair. If it’s the type of cable I’m thinking of, it’s cat5e at best (cat6 does not need to be shielded but can’t easily be accomplished in a flat cable).