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My laptop screen is (almost) black while my secondary screen is fine. I believe it to be backlight / brightness related.

Problem description

  • it starts when I start the laptop
  • system loads and works fine, just screen has problems
  • I can see the screen though very faintly / dimly - it's hard to see anything which ain't very white e.g. starting screen has big Thinkpad logo in white, large font - I can see it, though very dimly
  • second screen works very well

Official backligtht debugging:

  • using acpi setting as prescribed there for Thinkpads didn't help
  • I can see an entry in /sys/class/backlight/ and it changes when I press hotkeys for brightness (current backlight power for instance goes up or down)
  • acpi-off didn't helpm neither did acpi_backlight=vendor

Hardware data

Laptop is Thinkpad Edge with glossy screen. 4 processors, 2 cores, exemplary CPU data from cat /proc/cpuinfo reports Genuine Intel i5 (M 480 @ 2.67GHz).

OS is Ubuntu Lucid, 10.04 LTS, 64-bit, with Linux generic kernel (2.6.32-44) and GNOME 2.32.2 (though I doubt there lies the problem).

$ lspci | grep VGA
01:00.0 VGA compatible controller: ATI Technologies Inc M92 [Mobility Radeon HD 4500 Series]

$ lshw -C display
   description: VGA compatible controller
   product: M92 [Mobility Radeon HD 4500 Series]
   vendor: ATI Technologies Inc
   physical id: 0
   bus info: pci@0000:01:00.0
   version: 00
   width: 32 bits
   clock: 33MHz
   capabilities: pm pciexpress msi bus_master cap_list rom
   configuration: driver=radeon latency=0
   resources: irq:33 memory:c0000000-dfffffff(prefetchable) ioport:2000(size=256) memory:f0300000-f030ffff memory:f0320000-f033ffff(prefetchable)


I was NOT running any proprietary drivers, just checked with "Hardware drivers". There is one for ATI that is suggested there, though I didn't need it so far.

UPDATE: changing the driver to proprietary one (ATI/AMD FGLRX) didn't help.

Tried and failed

Resetting / running on power or battery / charging / getting rid of static electricity / warming up *doesn't help*

This is NOT a blank-screen problem, at least it isn't following official Ubuntu black-screen diagnostics - I can see my screen, though barely.

What I will try next: - check last updates I've made - IIRC I am running on nomodeset already, but will verify this

Any ideas how to proceed best? What is most probable cause?

share|improve this question
What happens if you disconnect the secondary screen ? – Suhaib Oct 21 '12 at 1:51
Thanks, Suhaib. Unfortunately - nothing. I just lose a screen that displays things well. No change on laptop screen - it stays near-black as it was. I plugged other monitor to see if it's a graphics problem or just my laptop screen problem - originally I worked only on my laptop, without secondary monitor. – LIttle Ancient Forest Kami Oct 21 '12 at 9:56
please provide some details on your system: platform type (desktop / laptop), computer model, graphics card and drivers installed etc., in addition, it may help to see the output of lshw -C display. – Eliran Malka Oct 21 '12 at 10:57
Thanks Eliran for spotting this. Certainly. I've edited my question with both hardware/driver data and with my new findings. – LIttle Ancient Forest Kami Oct 21 '12 at 19:39
up vote 0 down vote accepted

In the end it was a backlight problem. What led me to it, was that if I had a strong light source pointed at the screen - I could see well what was on it.

I took the laptop to service and it was fixed - backlight connection was loose.

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