[mythtvnz] mythtvnz Digest, Vol 178, Issue 3

[Stephen Worthington]

On Mon, 8 Sep 2025 09:35:50 +1200, you wrote:

>One minor issue i've noticed, after some time of not using my MythTV
>machine, the HDMI signal stops (screen blank?  power saving?  don't
>know...).  Problem is, it does not come back when i try to use MythTV - TV
>just says 'no-signal'.  I have to press <ctrl>-<alt>-F3 and then
><ctrl>-<alt>-F2 to get the screen working again.  Oddly, this only seems to
>happen when i run my TV at full 4K resolution.  If i run at 1080, then the
>MythTV screen always appears instantly when i switch back to it...    I'm
>running the nVidia 550 driver.
>
>I wonder if anyone else has noticed this?

If it was screen blanking, then just doing something that indicates
activity should unblank it.  Just tapping the shift key should do it.
But it sounds like what you are getting is the HDMI output in a mode
that is incompatible with your TV.  That might be happening when a
screen blanking is done, or when it tries to recover from blanking.

The first thing to do is to eliminate all the screen blanking methods.
There are three different ones that I know of.  First, in the desktop
settings, there should be a screen blanking option.  In Ubuntu, this
is usually using xscreensaver, but the options in the settings
normally do not mention the name of the program.  Anyway, set that
screen saver to disabled.  And also, if possible, make sure that the
xscreensaver program is not running and never gets started.  This
command will tell you if it is running:

sudo ps -ef | grep xscreensaver

and this one will kill it if it is running:

sudo pkill xscreensaver

Finding where xscreensaver is started from can be difficult - it
depends on what desktop software you are running.  I believe that if
you are using Gnome, disabling the screen saver settings in Gnome will
actually make it so xscreensaver does not get run at all.

The other two screensavers are in X.  One ("DPMS" if I remember
correctly) is disabled by putting this section in your
/etc/X11/xorg.conf file:

Section "ServerFlags"
        Option "BlankTime"              "0"
        Option "StandbyTime"    "0"
        Option "SuspendTime"    "0"
        Option "OffTime"                "0"
EndSection

If that file does not exist, just create it.  The after you have done
that, run these commands to give it the correct permissions and
ownership:

sudo su
cd /etc/X11
chown root:root xorg.conf
chmod u=rw,og=r xorg.conf
exit

Then reboot.

The third screensaver is very difficult to prevent from working.  Once
your system is booted and the desktop is showing, this command should
turn it off:

sudo xset s off

so the best I have come up with to automatically turn it off is to run
that command automatically some time after the desktop is up and
working.  Again, doing that depends on what desktop you are using, so
for now I would just suggest doing that manually while you are trying
to figure out this problem.  I leave this screensaver enabled as I am
using an OLED TV and want the screen to be blanked if I leave it for a
while, to prevent burn in.  The blanking time can be set with this
command:

sudo xset s 30

(for a 30 second blank time).

Other things to try when you have the screen blanked and it does not
recover on activity is to try unplugging the HDMI cable and plugging
it in again, and cycling the power on the TV.  When you do that, you
can look at the /var/log/Xorg.0.log file to see what screen mode
changes are happening.  If it is going into an invalid mode, it is
then possible to configure the valid modes in the xorg.conf file, but
this can be a very difficult thing to do properly.