2008 iMac display flickers and thefn freezes[video inside]

[andywallin]

So my 2008 iMac has for at least a year acted somewhat strange. It from time to time flickers and changes in light intensity for a couple of seconds.
Today, things escalated quite a bit. It just blacked out initially, but the music continued playing for maybe half a minute, then it froze completely. Upon reboot, the whole screen started to flicker as seen in the video, and eventually the system froze again. The longer it's turned of, the longer it runs before the screen flickers and disintegrates leading to the total stop of the system.

Any ideas? GPU? Logic board? Fixable? Thanks for any input!

Videos:
http://www.youtube.com/watch?v=TTlzz7UmwFo

http://www.youtube.com/watch?v=lgwvyl8wC-g

 

[Brian Y]

100% GPU I'd say.

Problem is, some of the 2008 ones had integrated GPUs, whilst some had dedicated. If it's a dedicated GPU, it's a fairly inexpensive swap if you can source one (from another dead iMac, eBay, or worst case scenario, iFixit).

If you don't have an dedicated graphics card, you'll be looking at a new MLB.

 

[Intell]

What GPU does your iMac have in it? What version of Mac OS X is it running? Does it still do this when you have started up from the reinstallation disc or a Snow Leopard retail disc?

100% GPU I'd say.

Problem is, some of the 2008 ones had integrated GPUs, whilst some had dedicated. If it's a dedicated GPU, it's a fairly inexpensive swap if you can source one (from another dead iMac, eBay, or worst case scenario, iFixit).

If you don't have an dedicated graphics card, you'll be looking at a new MLB.

None of the 2008 iMacs had an integrated GPU. They all had a GPU on a separate removable video card. It's the 2009 models with the Nvidia 9400M that have a GPU on the logicboard that requires a logicboard swap.

 

[andywallin]

Thanks for your input!

It's an 2.8GHZ INTEL CORE 2 DUO, and has an NVIDIA GEFORCE 8800 GS W/512MB. I use snow-leopard, of course . Yes, it still happens even though I boot it with the startup-disc. Are there other better gpu's that would be suitable or does it have to be the same model?

Again, thanks!

And by the way, is this diagnosable by apple hardware test? Couldn't get it to run holding the 'd'-key during startup.

 

[Intell]

Your GPU is likely failing. That particular GPU is known for having faults. The D at startup only works if the Mac is running its original OS or had its OS reinstalled from its reinstallation discs. If it did work, it would have only been able to test the Mac's ram. You'll need to take it to an Apple store to have it checked.