Hey Man, I have got the same issue with my new RSB-6.
My supplier said, it was because RSB-6 does support 4K but my TV doesn't, which was totally make no sense to me.
I have bought new HDMI cable and try but still doesn't work.
Right now, I am using the digital mode instead, it works fine, but I still need the HDMI to work, because the remote is very low quality and not going to last long.