I have just got a roku express and it's plugged in to HDMI port 2, I have the PS4 in HDMI port 1.
The issue is that when I have been on port 2 the roku box displays fine, and then when I switch back to port 1 for the PS4 the picture is gone, switching back to the roku box the picture is OK it's only knocking the picture out on the PS4 and only comes back by turning the TV off and on. It's extremely frustrating.
Re: New device causing other HDMI input to blackout
What happens if you swap which HDMI ports the two devices are connected to?
Does the problem:
Follow the PS4 to HDMI 2?
Stay with HDMI 1 which now has the Roku?
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