[Bug 69082] Re: Screen goes blank regardless

[Bryce Harrington]

It sounds like this may be your power management kicking in.

Note that your screensaver and your power management can each cause the
monitor to blank.  The screensaver usually displays something (flying
toasters, etc.) but one setting allows it to simply blank the screen.
Power management always just results in a black blank screen; sometimes
you can also tell it is on because the monitor's power button switches
from green to off or amber.

You can adjust this setting via System->Preferences->Power Management,
and then adjusting the settings for the display inactivity timeouts.

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Screen goes blank regardless
https://launchpad.net/bugs/69082