Laptop screen brightness stuck

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:

[email protected]:/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.

2022-07-25 20:41:40
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Answers: 0