[ltp] no brightness adjustment on t42 with/without linux

Henrique de Moraes Holschuh linux-thinkpad@linux-thinkpad.org
Sat, 26 Apr 2014 19:33:39 -0300

On Mon, 10 Mar 2014, Raider Sail wrote:
> I figure I've touched something in the embedded controller and there's no
> way to reset this through conventional means.

There is no such thing in the T4x.  The EC is easily powered down on the
T4x...  Any persistence is done through the NVRAM, by the BIOS... I don't
think IBM was crazy enough to use the "vital product data" eeprom to store
anything related to brightness control.

Unfortunately I cannot help you with the T42 NVRAM dump, but it might be
worth it to ask in the ThinkPad Forums.

Brightness in the T42 should be controlled by the EC, so either you got a
hardware defect somewhere in the planar, cables to the inverter or the
inverter itself, or the commands are not getting sent to the EC.

Enable backlight control in vendor mode for thinkpad-acpi, and check if it
can change the backlight.  Place it in EC mode if the default mode doesn't
work.  If it won't work no matter what, chances are high you have a hardware
defect.  Details at:


look for "LCD brightness control".

  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh