Power manager does not blank the screen

Submitted by Grigory

Link to original bug (#14716)

Description

I have linux mint tara with xfce. I have enabled option "Blank After X" minutes. I use LG display with HDMI with integrated intel core i7 graphics card.

What I expect: black screen that makes my display go in power save mode that turns off the light completely but keeps wait the any non zero pixel. What I see: after X minutes on the my display I see bright image and caption "check you cable".

Also I have tried almost all combintations, 4 simplest of them:

1. just blank after 1 minutes, Pot to sleep - never, Switch off - never
2. Blank - never, Pot to sleep - 1 minutes, Switch off - never
3. Blank - never, Pot to sleep - never, Switch off - 1 minutes
4. Blank - 1 minute, Pot to sleep - 10 minute, Switch off - 1 minutes the result is the same - "check cable"

`xfconf-query -c xfce4-power-manager -lv`
/xfce4-power-manager/blank-on-ac                    1
/xfce4-power-manager/dpms-enabled                   true
/xfce4-power-manager/dpms-on-ac-off                 0
/xfce4-power-manager/dpms-on-ac-sleep               0
/xfce4-power-manager/lid-action-on-battery          1
/xfce4-power-manager/lock-screen-suspend-hibernate  false
/xfce4-power-manager/logind-handle-lid-switch       true
/xfce4-power-manager/power-button-action            3
/xfce4-power-manager/show-panel-label               0

Version: 1.6.1