Since the iMac design changed to just having one big flat screen, the machines suffered from a problem, that owners of all similar designed computers hat to face: overheating. The first tell tale signs on an iMac are that the fans are becoming noticeably louder and the back of the machine, especially the heat exaust, is getting darker and darker. If you look closely you might even notice, that the upper edges of your display got tinted by the heat and you experience problems with your harddrive and dvd drive or even a failing power supply. Where the tinting is only a cosmetical problem and the harddrive, dvd drive and power supply are pretty cheap (but not easy) do-it-yourself repairs, there is one damaging effect from heat that is rather expensive: a deformation of the logic board. When you hear of this for the first time you might not believe it, but investigating it a bit more it seems that this problem is not only quite common among all-in-one devices but also among notebooks and game consoles. The effect from a deformation of the logic board is mainly that the connections between the little pins of the chips that are soldered on it become faulty, comparable to a broken cable on your headphone. The effect from this can be, that you not only get stripes on your screen but also your whole machine freeses, when using Mac OS.
A permanent fix is called "reballing". To get a better idea of this process you might want to watch this video. Nevertheless this fix is permanent and not that expensive, it is rather annoying to get the logic board out of your iMac and on top of it, it might not even solve your problem because it is not 100% sure, whether it is not the graphic chip itself, that is faulty. Anyhow if you're willing to experiment a bit and give Ubuntu a try you can still make use of your machine by applying a little trick that uses the graphic card in a less demanding way, what is to my knowledge not possible with Mac OS. You might still see some strange points on your screen, but trust me, this is much less annoying (comparable to dead pixels) and you at least get a stable computer again. If you want to install Ubuntu on an iMac you might want to read this article first.
The Solution to graphic problems with Ubuntu on an iMac: Disable KMS
You can only do this at boottime, c.f. ubuntu must boot with this option everytime it starts up. To achieve this you have to edit only one file and execute one command after you see the Ubuntu desktop the first time, here is how it goes:
- Press ALT and F2, enter sudo gedit and hit enter: after entering the administrator password a text editor should apear
- Open the file /etc/default/grub, look for this line
and change it to
- save the file and close the window
- to now make this change permanent, again hit ALT + F2 and enter gnome-terminal
- here enter sudo update-grub and hit enter, after again entering the administrator password Ubuntu will make the changes permanent
- reboot to apply the changes
- if everything went well you now should have a stable computer again, running even faster then with Mac OS
Some more notes concerning graphic problems when using Ubuntu on an imac:
No Proprietary Drivers for Intel Imac's (former G5) ATI-Graphics Card anymore
Unfortunately ATI no longer updates the drivers for a lot of older but then not that old products, as written here. This means that you might not be able to get the full power of your graphic chip anymore, since you can only use the legacy open source drivers You can still use all the desktop effects with ubuntu, but everything might not be as fast as possible. With everyday tasks, you might not even notice the difference, since you have all the desktop effects, can watch movies and dvds and even youtube works in full screen.
Problems with Ubuntu 10.04 and newer versions (maybe only with damaged grafic chips)
With a fresh install or an upgrade to Ubuntu 10.04 you might experience some annoying problems with the behaviour of your graphics card. When using Flash in a Browser or using wine with a program, that doesn't ask for a lot of performance, you might actually freeze your system. Actually you don't really freeze the system, since the cpu load stays the same, but you freeze your graphical user interface. With Mplayer or any other player using xvideo, you also experience a wierd group of stripes sorrounding rapid movements. It reminds you a bit on what you see, when you have to activate deinterlacing, but than it's still different. Anyhow: it's pretty annoying. Funny part here is, when you enable compiz (and haven't enabled "Undirect Fullscreen Windows" in CompizConfig") you don't see this error.
After looking into that problem a bit I set my bets on KMS (Kernel Mode Setting) beeing responsible for the problems with Ubuntu 10.04 since I understood, that KMS was introduced to the ATI graphic cards (Imacs also use theses cards) with version 10.04. As I read it, the biggest advantage is that the kernel (the basic piece of software linux/ubuntu runs on) can now directly access the graphic card, without having to use a driver in between. One of the biggest "advantages" is, that you can now have a more shiny startup animation while booting and for the sake of this experience a lot of problems. The above trick disables KMS.