Getting garbled screen when lowering the brightness on Ubuntu 12.04

Asked by Tejas Jammihal on 2012-05-10

Whenever I try to reduce the brightness of my laptop running Ubuntu 12.04, after lowering 2-3 steps the sreen becomes garbled with huge pixels of random colours and some of are flashing.
I tried with the hardware key as well as using the Brightness applet, but the error persists.

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Ubuntu xserver-xorg-video-ati Edit question
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actionparsnip
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actionparsnip (andrew-woodhead666) said :
#1

Any chance of a make and model of the system....probably the MOST important piece of information you could give?

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Tejas Jammihal (tejjammy) said :
#2

Sorry for that.

Dell Studio 1558

Processor: Intel i5 M 430
Memory: 4GB
Graphics: ATI Mobility Radeon HD5470

If anything else needs to be given please tell.

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actionparsnip (andrew-woodhead666) said :
#3
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Best actionparsnip (andrew-woodhead666) said :
#4

Seems you need the boot option:

acpi_backlight=vendor

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Tejas Jammihal (tejjammy) said :
#5

Thanks actionparsnip, that solved my question.

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actionparsnip (andrew-woodhead666) said :
#6

Why could I find that and you couldn't when we connect to the same internet......

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Tejas Jammihal (tejjammy) said :
#7

Probably because I'm still a new user and don't know where to look at. Also I dont trust solutions posted at random sites because I could potentially end up screwing my PC.

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actionparsnip (andrew-woodhead666) said :
#8