Backlight can't be turn on in Acer Aspire 4736

Solution 1:

Here is a solution that worked for me on Ubuntu 11.10 based on http://lare-india.blogspot.com/2011/09/ubuntu-upgrade-caused-blank-screen-on.html

Boot your laptop into Ubuntu.

Connect an external monitor or sit with your back towards a sunny window so the sunlight helps to illuminate the screen (a flashlight can help too).

Press Ctrl+Alt+T to open a terminal and type:
sudo nano /etc/rc.local

You will be prompted for your root password, which was set when you performed the install. Type it in and hit Enter.

Press your down arrow key to move the cursor to the last line and hit Enter

Press your up arrow key once and type:
setpci -s 00:02.0 F4.b=00

Press Ctrl+O to save and Ctrl+X to exit.

Now back in the terminal type:
sudo nano /etc/default/grub

Find the line
GRUB_CMDLINE_LINUX_DEFAULT = "quiet splash"
and edit it to
GRUB_CMDLINE_LINUX_DEFAULT = "quiet splash acpi_osi = Linux"

Press Ctrl+O to save and Ctrl+X to exit.

Back in the terminal enter:
sudo update-grub2

Once it completes, enter:
sudo reboot

Your computer will reboot and when Ubuntu boots back up, you should be able to see the screen with no problems.

Solution 2:

I've experienced similar issues with another Acer notebook which was running Ubuntu from a Kubuntu 10.04 32b Live CD (for testing purposes). Before starting up, the backlight was fine. In a later stage, the backlight suddenly turned off.

Luckily, I can remember the commands from my head, so I pressed Ctrl + Alt + F1 to switch to a virtual console. Since I am already logged in on a Live CD I ran:

cat /sys/class/backlight/acpi_video0/max_brightness | sudo tee cat /sys/class/backlight/acpi_video0/brightness

Unfortunately, the backlight turned off again after switching back to the GUI using Ctrl + Alt + F7, so I created a script that should be run in the GUI:

echo 'cat /sys/class/backlight/acpi_video0/max_brightness | sudo tee cat /sys/class/backlight/acpi_video0/brightness' > lite

When switching back to the GUI, I pressed Ctrl + Alt + T to open a Terminal and run:

. lite

Now as long as I stayed in this GUI without switching to a virtual console and back, the backlight would be OK.

Configuring the backlight through /sys/class/backlight/acpi_video0/brightness is a workaround, perhaps there is already a bug report on Launchpad. Otherwise, you could put the above cat .... brightness command in a startup script which will workaround the problem for now.