This is obviously a software or firmware fault in the Roku device - nothing to do with the TV, which displays normal behavior on all the other HDMI settings that can be selected.
Playing a YouTube video, showing a completely black screen (but with sound), pressing the Back button brings up the YouTube page with everything visible as normal, except for black in the one I'm trying to view.
A system reset has always (so far) fixed the problem for another 24-48 hours, but is a nuisance. And why has it only just started to happen?
i upgraded my old streaming stick to a Roku Express 3960RW and the incompatibility started on day one. Please refer to my reply to Mal4romcal for the whats and how it's now fixed!
p.s. I should have been clearer. I have a Roku Express streaming device, not a Roku smart TV. I am having the problem with what the Roku box is sending to my (vintage Pioneer plasma) TV via HDMI.
Have you tried the Roku on another tv? Also try another device on the HDMI port to make sure that the port isn't the issue. If the Roku doesn't work on other TVs either then try to use a different HDMI cord. Try all of these things and let me know how it goes.
Bear in mind that when I press Back on the Roku remote control, the black screen is replaced with the normal YouTube display. So suddenly the HDMI cable and TV input have come to life? Seems unlikely.
Next time the problem occurs I plan to do the following.
The TV has three HDMI inputs, currently used for two Humax PVRs and the Roku device. I shall unplug the HDMI cable from the Roku device, then unplug one of the PVRs and use its HDMI cable to connect the Roku device. On selecting the new input on the TV, so that it is seeing the Roku device, I confidently predict the black screen will reappear.
Watch this space.
