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the external display works fine but my main display is just black i know it works beacuse it works fine in windows but it wont work in linux D: my laptop is a acer-aspire 5734z ive tryed reinstalling ubuntu and it still dosent work. help???

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There's a kernel bug that affects Acer laptops. Basically, the backlight isn't being turned on. You can read the bug report here.

The bug hasn't been fixed, but there's a workaround:

In short, the answer that worked for me was two-fold: first, place the following in /etc/rc.local:

setpci -s 00:02.0 F4.B=0

That should make the backlight turn on. You can run the command from the command line to test it, but from the command line, be sure to put sudo in front.

Then, if the backlight doesn't come on after the computer goes into power-saving mode, put the command into root's crontab. Run sudo crontab -eu root and insert the following line:

*/1 * * * /usr/bin/setpci -s 00:02.0 F4.B=0

This will cause the backlight to turn on no more than one minute after the computer resumes.

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