i have a 15+ year old Marantz SR 5004 receiver and a Panasonic DP UB820 4k player.

I barely use the 4k player as mostly just use an old PC via HDMI to the Marantz with the HDMI out from the Marantz to HDMI on the TV

Anyway I went to play a Blu Ray DVD and it would not work. The timer is counting on the Panasonic but there is no signal to the TV. 

First thought was swap the HDMI cable but this didnt help

What is really odd is, while keeping everything exactly the same, I can play my old DVD's and the one 4k DVD I have (Alien Convenant) ie I get video and sound (Dolby Digital True HD) for the 4k DVD. But none of the Blu-Rays play

How on earth could that be? I have a dozen blu-rays they cant all be faulty.

Made no difference if I changed sound settings on the Panasonic from Bitstream to PCM

If I connect the Panasonic directly to the TV all discs work including the Blu-rays so obviously it is not an issue with the player. (I use the video out HDMI on the Panasonic)

I guess it might be a HDCP issue as the Marantz only has HDMI 1.4 but then why does the 4K disc play? This also rules out if being an issue with the cable?

I guess I should try putting the video out from the player directly to the TV and use the audio out NDMI on the player to the Marantz although I prefer not to do that as at present the cables are all routed in the wall to the tv to keep things clean