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I just replaced the broken screen on my Thinkpad Edge 13". Now the brightness-adjustments via the FN keys don't work anymore (the brightness indicator bar goes from Low - Full, but nothing actually changes).

ls /sys/class/backlight/*/brightness
/sys/class/backlight/intel_backlight/brightness
/sys/class/backlight/thinkpad_screen/brightness

Both have very different values for max_brightness (7 (thinkpad) and 4422465 (intel), but nothing changes "echoing" a smaller.

I changed

GRUB_CMDLINE_LINUX_DEFAULT="quiet, acpi_backlight=vendor"

and ran update-grub.

What else can I try?

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1 Answer 1

This looks to me like a hardware problem. Did you change the backlight as well, or the display only? If you changed backlight as well, it may be incompatible. Or maybe you have damaged one of the wires which go through the hinges while (dis-)assembling parts.

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With the thinkpad edge, if I'm not wrong, Backlight&Display are a single unit, and I changed the whole unit. I replaced it with original hardware, but used this time a ratt screen instead of a reflective one. –  rer Jan 13 '13 at 18:58
    
There are different versions of backlight control in thinkpads used. Some thinkpads have standard ACPI backlight control, some have issues with their ACPI-tables and some use other way of controlling backlight. First you should make absolutely sure you have no compatibility problem, even with "original" parts. Then you can try the appropriate method for your thinkpad-model described here: thinkwiki.org/wiki/LCD_Brightness And finally it is possible you need a BIOS update after switching to a newer version of backlight, if this is supported for your model. –  diamy27 Jan 14 '13 at 5:38
    
And then read this: wiki.ubuntuusers.de/Thinkpad_ACPI –  diamy27 Jan 14 '13 at 5:51
    
Thank you very much for your replies. I carefully worked through the thinkwiki and the Thinkpad_ACPI text. I tried all possible solutions listed there; in fact my Thinkpad ACPI is working perfectly, it's just not controlling the display brightness correctly. At this point I think there might in fact be a compatibility problem. I updated the BIOS to the newest version, but still /sys/class/backlight/intel_backlight/brightness has a confusigly high value "max_brightness" of 4422465 and doesn't respond to my input. Can you suggest me how to verify or rule out a compatibility problem? –  rer Jan 14 '13 at 13:04
    
Sorry, but this is the point I can't give further advice, since I am not an expert but a technically interested layman only. Well, you could ask the manufacturer of your notebook, he should know about possible compatibility issues of his backlights. If this is no way for some reason you could try to plug your old broken display (at least the connectors for the backlight) on the fly (without actually mounting the parts) for testing, and see if the old backlight works correctly.If so, you could try to get datasheets of the two backlights to find the differences in the electrical properties. –  diamy27 Jan 15 '13 at 0:50
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