I have a Samsung 22 inch 1080 HDMI input television that I use for experimentation with my Raspberry Pi and other SBCs.
I noticed something interesting - On my Pi Zero, when the default Raspbian screensaver is triggered, the monitors backlight shuts down indicating that it is properly going into low power standby.
On my Raspberry Pi 3b, when the same thing happens, the screen blanks to dark grey, but the backlight is still on, which would seem to indicate that the Pi 3b is not properly triggering the screen to go into low power standby.
Tried this with both an older Jessi, and the current Stretch release, and I just can't get HDMI standby to work.
With the EXACT SAME microSD in the Pi Zero, and Pi 3, on the Pi Zero, the screen blanks and shuts down properly, where that same microSD in the Pi 3b gives a dark grey screen, with the backlight still enabled.
The hack of using tvcontrol to just KILL the HDMI output completly is not an option for me because the Samsung handles this by stupidly displaying a "No Input" message for about 15 or 20 minutes before shutting down.
I tried to force the HDMI blanking output to standby using: xset dpms force standby, and xset dpms force off, but the tv output still just blanks to a dark grey with the backlight still enabled on the Pi 3b.
Does anyone have any idea how to get the HDMI power save mode working on the Pi 3 ???