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I can no longer adjust the brightness of my laptop screen, it's stuck at the lowest.

In Linux, the brightness adjustment keys (Fn + F4/F5) still work, since a brightness popup shows and the meter bar changes, but it does this in a strange way. Starting at 100%, each successive press of the "lower brightness" button moves the bar to:

  • 67%
  • 50%
  • 0%
  • 26%
  • 12%

Or another random pattern like that. The problem is not Linux however, since I can't change the brightness from Windows (7) either.

Where do I even begin to look? Since the problem does not seem be OS-specific, I've searched in the BIOS, but it has no option like that. I've also removed the power from my PC (including removing the battery) for about a minute but that changed nothing.

How did this happen? I think it's been this way since when I lowered the brightness to 0%, then pressed the "lower brightness" key again. Not sure about that though.


In response to the file in proc: The file exists. If I read it, it shows:

root@bart-laptop:/home/bart# cat /proc/acpi/video/VGA/LCD/brightness 
levels:  70 50 20 30 40 60 80 90 100
current: 100

If I echo a different level to it it changes the value in the current: field above, but there's no actual change. Also the numbers behind levels: are in a strange order.


For thoroughness' sake I've disconnected the CMOS battery to reset the BIOS settings. The settings were reset but the problem remains.

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Let us know how attempting to change the brightness via software goes. In windows 7, there should be a slider that allows you to change the brightness via software controls (left-click on the battery icon in the system tray, then left-click on the "adjust screen brightness" link. In linux, there are bios-level controls buried somewhere in /proc, depending on the version of the kernel you're using. –  Babu May 23 '10 at 17:13
1  
I've tried that in Windows, doesn't work. This is what led me to conclude that it's not the OS. How would I go about using those things you mention in Linux? –  Bart van Heukelom May 23 '10 at 17:47
    
Which model of laptop do you have, for information? –  Gnoupi May 23 '10 at 19:28
    
It's a custom one but the base is an MSI MS-1651, with a GeForce 9800M GS (if the graphics card has anything to do with it) –  Bart van Heukelom May 23 '10 at 20:15
    
I was thinking something along the lines of 'echo -n 100 > /proc/acpi/video/VGA/LCD/brightness', but I'm unsure whether or not the brightness file is still in the same location. The /proc directory, from what I've read, does get rearranged from time to time. The integer should be any number from 0 to 100, according to linuxscrew.com/2007/10/25/… –  Babu May 24 '10 at 0:19
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1 Answer

up vote 1 down vote accepted

A possibility would be that the specific laptop keys for this setting is faulty, hardware speaking.

I base this possibility on something which happened to me with my previous laptop. With time of using it, the plastic eventually moved a bit so that the "volume down" (placed just over the keyboard, under the screen) was all the time in contact.

For information, I fixed this by opening the top plastic part, and putting a piece of paper between the button and its contact. Then I used only the Fn shortcut.

I don't know if you have the same problem (nor if it's even possible, not knowing which model is your laptop), but the fact that this is happening for all OS tend to show that it could be a simple hardware problem like that.

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In my question: "In Linux, the brightness adjustment keys (Fn + F4/F5) still work" So thanks, but that's not it ;) –  Bart van Heukelom May 23 '10 at 17:46
    
@Bart - If there is for example the "brightness down" key pressed all the time, then it could be that in Windows it's like pressing non stop, and preventing you from increasing, even with another key, and that in Linux it would work differently (maybe take care of the pressed key only once you press another "brightness related" one). I don't really know, it's just a wild guess. –  Gnoupi May 23 '10 at 19:27
1  
@Bart: Gnoupi's explanation of a stuck key is possible. One OS may act upon key-down and the other upon key-up, or their behavior may vary when two keys are pressed at the same time. –  harrymc May 26 '10 at 6:06
    
Well it was indeed a hardware fault, but in the display cable. –  Bart van Heukelom Jun 8 '12 at 9:43
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