iMac A1224 video display issue

[austinringding]

I've got an Early 2008 iMac; model A1224 EMC 2210.

I was surfing the web the other night, and the system hung. When i forced a power down, and then restarted it, it came up with a messed up display. See the photos:

This comes up everytime i reboot now. I can't even see anything unless i go into safe mode, and then I can at least (sort of) see the menus etc.

I've tried resetting PRAM, i've reseated / replaced RAM, tried a different hard drive with fresh install of OSX, set up an external monitor and connected to iMac remotely from another Mac via VNC application and I still get the weird display no matter what.

I am determined to fix this but need some direction on what needs to be done.

I'm thinking it's the video card, not the motherboard. Thoughts?

What is my next troubleshooting step?

Thanks in advance!!

 

[Intell]

That is very likely a failed GPU. What video card does it have in it right now? Does the problem persist when using an external screen?

 

[austinringding]

Yes, i hooked up an external LCD and the issue was still there.

It only extended my desktop to the external LCD, but the lines etc were still there.

It has the original video card, and according to EveryMac.com, it is an ATI Radeon HD 2600 PRO graphics processor -- using PCI Express -- with 256 MB of GDDR3 video memory.

I haven't removed it so I can't get the exact part number off of it, but i think it's
661-4426

 

[Intell]

Are you sure that iMac has the ATI card and not the Nvidia 8600? The Nvidia cards in this iMac fail because of the Nvidia 8600/8800 GPU flaw. You can replace the card with either the ATI 2400, ATI 2600, or a fixed Nvidia 8600.

 

[austinringding]

I do not know for sure.

How can one tell?

If we are over 90% sure that replacing the GPU / video card will resolve the issue, then i i will continue my dis-assembly and find out exactly what card is in there, and purchase a replacement.

Are we sure that it's GPU?

 

[Intell]

I'm about 90% sure that's a failed GPU. Boot it up in Safe Boot and click on the Apple menu and go to About this Mac, then More Info... In the Displays section, it'll tell you which GPU you have.

 

[austinringding]

if you have a minute, could you take a look at this ebay auction:
http://tinyurl.com/dxbpjsv

and tell me if that video card will work for my imac?

 

[Intell]

If your iMac is a 24" model, that will work.

 

[austinringding]

Mine is not 24"; rather 20". I see in the title that it says 24", but yet the part number seems to be the same as what i've seen for the 20".

I'd like to find a replacement part soon, but am having trouble pulling the trigger as i'm not positive on the part number.

Any other input on this issue?

 

[Intell]

The heatsink for the 20" and 24" models is different. And it is different for ATI and Nvidia cards. Thus, there is a total of four heatsinks. You can get just the card if you know which GPU your iMac currently has in it and use your current heatsink.

 

[austinringding]

OK, that makes sense.

I'll get into it a little more this evening or tomorrow or later this week depending on when i have the time.

Then i can be sure of which card i have before i order.

Thanks a bunch!

 

[Nathan1]

Hey Austin & Intell,

I've very recently been experiencing the same problem with my iMac and came across your forum. I see your last post was on 6/6/13, have you had any luck diagnosing the problem? I loathe to go to the Apple store but at this point it's looking like my only option. Please Help!

Thanks in Advance!