laptop LVDS screen blanks if external VGA display connected

[Andrej Surkov]

Since I connected external VGA (D-sub) monitor laptop's main LCD display allways blank and black, whatever screen combinations and options I've tried with xrandr or LXrandr GUI.

When executing randr LCD flashes with sublight but show no picture, it's just blank.

In Windows 7 LCD display works well with or without external display.

Unpugging external display make LCD work well.

laptop is netbook Asus X101CH with Ubuntu 14.04 32-bit with latest updates
video is Intel CedarView builtin GMA3600
xrandr output below

$ xrandr
Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 4096 x 4096
VGA-0 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 531mm x 298mm
   1920x1080 60.0*+
   1680x1050 60.0
   1600x900 60.0
   1280x1024 75.0 60.0
   1280x800 59.8
   1152x864 75.0
   1280x720 60.0
   1024x768 75.1 60.0
   832x624 74.6
   800x600 75.0 60.3
   640x480 75.0 60.0
   720x400 70.1
LVDS-0 connected (normal left inverted right x axis y axis)
   1024x600 60.0 +
   960x600 60.0
   960x540 60.0
   800x600 60.0 60.3 56.2
   840x525 60.0 59.9
   800x512 60.2
   700x525 60.0
   640x512 60.0
   720x450 59.9
   640x480 60.0 59.9
   680x384 59.8 60.0
   576x432 60.1
   512x384 60.0
   400x300 60.3 56.3
   320x240 60.1
DVI-0 disconnected (normal left inverted right x axis y axis)
DisplayPort-0 disconnected (normal left inverted right x axis y axis)

But I recall with HDMI external monitor everything was OK

[Igor (sheva)]

Same issue with my laptop. After fresh 16.04 install laptop's display active but blank.

# lshw -c video
  *-display
       description: VGA compatible controller
       product: Trinity [Radeon HD 7640G]
       vendor: Advanced Micro Devices, Inc. [AMD/ATI]
       physical id: 1
       bus info: pci@0000:00:01.0
       version: 00
       width: 32 bits
       clock: 33MHz
       capabilities: pm pciexpress msi vga_controller bus_master cap_list rom
       configuration: driver=radeon latency=0
       resources: irq:39 memory:c0000000-cfffffff ioport:5000(size=256) memory:d6000000-d603ffff

# xrandr
Screen 0: minimum 320 x 200, current 1440 x 900, maximum 16384 x 16384
LVDS connected (normal left inverted right x axis y axis)
   1366x768 59.99 + 40.00
   1280x720 59.86
   1152x768 59.78
   1024x768 59.92
   800x600 59.86
   848x480 59.66
   720x480 59.71
   640x480 59.38
VGA-0 connected primary 1440x900+0+0 (normal left inverted right x axis y axis) 408mm x 255mm
   1440x900 59.89*+ 74.98
   1280x1024 75.02 60.02
   1024x768 75.08 70.07 60.00
   832x624 74.55
   800x600 72.19 75.00 60.32 56.25
   640x480 75.00 72.81 66.67 60.00
   720x400 70.08
HDMI-0 disconnected (normal left inverted right x axis y axis)

I suppose this issue related to radeon driver, because on my previous installation(Ubuntu 14.04, fglrx driver) all worked fine.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Gauransh Kumar (gauranshk)]

I am also facing the same issue.
Currently using Kubuntu 20.04LTS

When I connect VGA monitor in Windows it works perfectly, but when I connect it to Ubuntu it only shows the output on VGA display and the LVDS turns black. If I connect a monitor via HDMI it works perfectly in Ubuntu.

Any solution please !!