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[Erwin <erwin.gaubitzer@xxxxxxxxx>]

I also have the NP770Z5E. What helped me was to change the grub kernel
boot parameter to

acpi_osi=linux acpi_backlight=video

in /etc/default/grub (line GRUB_CMDLINE_LINUX_DEFAULT=) (I have Debian Linux). Hint was found at
https://wiki.archlinux.org/index.php/Backlight#Kernel_command-line_options

After command "update-grub" and reboot changing brightness was possible
again.

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https://bugs.launchpad.net/bugs/1485246

Title:
  Backlight issue - Samsung Chronos 7 (model - NP770Z5E)

Status in linux package in Ubuntu:
  Confirmed

Bug description:
  Control of screen backlight is broken with a default clean install of
  Ubuntu 15.04 on my Samsung Series 7 Laptop (NP770Z5E). Setting kernel
  parameter 'acpi_backlight=vendor' fixes the issue after two reboots.
  Debugging information attached as per -
  https://wiki.ubuntu.com/Kernel/Debugging/Backlight

  ProblemType: Bug
  DistroRelease: Ubuntu 15.04
  Package: linux-image-3.19.0-25-generic 3.19.0-25.26
  ProcVersionSignature: Ubuntu 3.19.0-25.26-generic 3.19.8-ckt2
  Uname: Linux 3.19.0-25-generic x86_64
  ApportVersion: 2.17.2-0ubuntu1.2
  Architecture: amd64
  AudioDevicesInUse:
   USER        PID ACCESS COMMAND
   /dev/snd/controlC0:  mark       1699 F.... pulseaudio
  Date: Sat Aug 15 21:36:20 2015
  HibernationDevice: RESUME=UUID=c4899b44-3e19-4e62-921d-cf0a1cef97ec
  InstallationDate: Installed on 2015-08-12 (3 days ago)
  InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422)
  MachineType: SAMSUNG ELECTRONICS CO., LTD. 770Z5E/780Z5E
  ProcFB:
   0 inteldrmfb
   1 radeondrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.19.0-25-generic root=UUID=5a02817b-1f9b-4abc-93a3-b10d5d9278ed ro quiet splash acpi_backlight=vendor vt.handoff=7
  PulseList:
   Error: command ['pacmd', 'list'] failed with exit code 1: Home directory not accessible: Permission denied
   No PulseAudio daemon running, or not running as session daemon.
  RelatedPackageVersions:
   linux-restricted-modules-3.19.0-25-generic N/A
   linux-backports-modules-3.19.0-25-generic  N/A
   linux-firmware                             1.143.3
  SourcePackage: linux
  UdevLog: Error: [Errno 2] No such file or directory: '/var/log/udev'
  UpgradeStatus: No upgrade log present (probably fresh install)
  dmi.bios.date: 09/05/2013
  dmi.bios.vendor: American Megatrends Inc.
  dmi.bios.version: P05ABU.142.130905.SK
  dmi.board.asset.tag: No Asset Tag
  dmi.board.name: NP770Z5E-S02UK
  dmi.board.vendor: SAMSUNG ELECTRONICS CO., LTD.
  dmi.board.version: SEC_SW_REVISION_1234567890ABCD
  dmi.chassis.asset.tag: No Asset Tag
  dmi.chassis.type: 9
  dmi.chassis.vendor: SAMSUNG ELECTRONICS CO., LTD.
  dmi.chassis.version: N/A
  dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrP05ABU.142.130905.SK:bd09/05/2013:svnSAMSUNGELECTRONICSCO.,LTD.:pn770Z5E/780Z5E:pvrP05ABU:rvnSAMSUNGELECTRONICSCO.,LTD.:rnNP770Z5E-S02UK:rvrSEC_SW_REVISION_1234567890ABCD:cvnSAMSUNGELECTRONICSCO.,LTD.:ct9:cvrN/A:
  dmi.product.name: 770Z5E/780Z5E
  dmi.product.version: P05ABU
  dmi.sys.vendor: SAMSUNG ELECTRONICS CO., LTD.

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