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From: Thomas McCullough on 19 Dec 2009 12:30
Hi all,
I am not sure who this should be addressed to, so here it is. I have
checked all the bugs I could find online and I don't think this one is
documented yet. I am experiencing a seemingly random backlight problem with
my installation (squeeze, constantly updated on an ACER Aspire 7720 laptop
with two SATA hard drives; the original vista on the first 160 Gb drive and
linux on the second identical 160 Gb drive with grub2 fully installed). I
have no brightness control using the keyboard (fn+left/right arrows) and no
OSD. Most of the other hotkeys seem to work; fn+f4 for sleep, volume is
controllable (more or less) with the side wheel and mute fn+f8, wireless
button, etc. If I put the computer to sleep then wake it up it (usually?)
comes back with very reduced backlight brightness. When the problem
appears, I get either very low backlighting or no backlighting at all. Once
it has happened, it won't even turn on during bios boot. It can be restored
by removing the battery, by booting into vista, which is done blindly, or...
by installing ubuntu live 9.10 cd. when I insert the cd and reboot the
computer, the backlight does not come on until the X server starts. I am
thinking there is a bios bug, since even the acer splash screen is dark, but
apparently the ubuntu team has found a workaround that restores whatever has
been changed in persistent memory. I would be glad to send all data from my
system that can help. I am fairly well versed in linux and am comfortable
using the command line. This is a very annoying bug that completely
disables the computer until one of the above resets is accomplished. Please
let me know what I can do to help resolve this issue.

thanks in advance,
tom mccullough
From: Thierry Chatelet on 19 Dec 2009 13:20
On Saturday 19 December 2009 18:07:11 Thomas McCullough wrote:
> Hi all,
<SNIP>

Hi,
Same problem with Acer Aspire 5712Z. I posted here some time ago about it, but
got no answer solving the problem. And then it want away with a kernel
upgrade, and came back with a new upgrade. I found 2 others ways to get out of
it when it happen: I have created a second user, and logging back and forth to
the second user brings back the backlight to full strength. No way to set it
using the function, but it's work. The second way is to go to console,
CTRL+ALT+ F1, try to change the brightness, it will show an error, then go
back to the regular user, problem is fixed!
At least, I dont have to go back to vista!!!!!


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From: Camaleón on 19 Dec 2009 14:00
On Sat, 19 Dec 2009 19:16:07 +0100, Thierry Chatelet wrote:

> On Saturday 19 December 2009 18:07:11 Thomas McCullough wrote:
>> Hi all,

> Same problem with Acer Aspire 5712Z. I posted here some time ago about
> it, but got no answer solving the problem. And then it want away with a
> kernel upgrade, and came back with a new upgrade. I found 2 others ways
> to get out of it when it happen: I have created a second user, and
> logging back and forth to the second user brings back the backlight to
> full strength. No way to set it using the function, but it's work. The
> second way is to go to console, CTRL+ALT+ F1, try to change the
> brightness, it will show an error, then go back to the regular user,
> problem is fixed! At least, I dont have to go back to vista!!!!!

Can you both please run "dmesg | grep brightness" and copy/paste the
output after you press the function key to change the brightness of the
screen?

BTW, it seems to be related to this kernel bug:

Buggy _BCM - acer aspire 5720G, 5710Z, 5315
http://bugzilla.kernel.org/show_bug.cgi?id=13121

(see comment #28 for other possible affected Acer laptop models)

Greetings,

--
Camaleón


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From: Thierry Chatelet on 19 Dec 2009 14:20
On Saturday 19 December 2009 19:56:10 Camaleón wrote:
>
> Can you both please run "dmesg | grep brightness" and copy/paste the
> output after you press the function key to change the brightness of the
> screen?
>
> BTW, it seems to be related to this kernel bug:
>
> Buggy _BCM - acer aspire 5720G, 5710Z, 5315
> http://bugzilla.kernel.org/show_bug.cgi?id=13121
>
> (see comment #28 for other possible affected Acer laptop models)
>
> Greetings,
>
Here it is:
ACPI: Failed to switch the brightness

but when the backligth is really dim and I press the function key for
brightness, I get a message saying somethng about wrong value for it. I will
write it when it happen. ( I don't want to stop/start the laptop until it goes
wrong. Every forth, fifth time).
Thanks
Thierry


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From: Camaleón on 19 Dec 2009 16:40
On Sat, 19 Dec 2009 20:13:26 +0100, Thierry Chatelet wrote:

> On Saturday 19 December 2009 19:56:10 Camaleón wrote:
>>
>> Can you both please run "dmesg | grep brightness" and copy/paste the
>> output after you press the function key to change the brightness of the
>> screen?
>>
>> BTW, it seems to be related to this kernel bug:
>>
>> Buggy _BCM - acer aspire 5720G, 5710Z, 5315
>> http://bugzilla.kernel.org/show_bug.cgi?id=13121
>>
>> (see comment #28 for other possible affected Acer laptop models)
>>
> Here it is:
> ACPI: Failed to switch the brightness
>
> but when the backligth is really dim and I press the function key for
> brightness, I get a message saying somethng about wrong value for it. I
> will write it when it happen. ( I don't want to stop/start the laptop
> until it goes wrong. Every forth, fifth time).

It seems many other people is experiencing that same issue:

***
Unable to set brightness
http://bbs.archlinux.org/viewtopic.php?id=76799
***

And they also point-out to the kernel bug.

Carefully review the messages posted on that forum and look for any
possible bypass mentioned, if any :-?

Greetings,

--
Camaleón


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