iMac 24" 2008 Problem

It appears that we have the same, or almost the same, iMac. Mine is an A1225 "iMac8,1", 24-inch Early 2008 with 2.8 GHz Core2Duo. Mine has ATI Radeon HD 2600 Pro graphics, but some Early 2008's had some NVIDIA card that was (I think) more prone to failure.

Which graphics card does your have?

Unfortunately, I don't think I can help much. It seems you've tried everything I can think of. I would be cautious about assuming that the video card is the problem, because I thought the logic board LEDs were supposed to indicate video card problems, and you say your LEDs are all OK. Of course I might be wrong and maybe some video card problems don't show on the LEDs...

If yours has the NVIDIA card, what I've read about it would make me not bother getting it repaired. Instead, I'd look for the Radeon HD 2600 Pro like mine has. I think I've seen them on eBay, but not cheap.

What you really need is someone you can borrow a compatible card from -- to verify that yours is actually the problem. (Sorry, I can't lend you mine -- I need to use it!)

If you have the original OS X installation DVDs (should be OS X 10.5 Leopard) -- does the machine fail to boot from them, too? I see you've installed Yosemite, and that should work. (I haven't tried Yosemite yet -- currently running 10.8.5 Mountain Lion.)

If you can't borrow a graphics card, I guess you'll have to take a chance or give up.

Found this in an old iFixit web page I saved to my drive, but you probably know this info already:

LED 1 - Indicates that the trickle voltage from the power supply is detected by the main logic board. This LED will remain ON while the iMac is connected to the AC power. The LED will remain on even when the computer has been shut down or put to sleep. The LED will turn off only if the AC power is disconnected or the power supply is faulty.

LED 2 - Indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly.

LED 3 - Indicates that the computer and the video card are communicating. This LED will be ON when the computer is communicating properly with the video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the video card might be installed incorrectly or need replacement.

LED 4 - Indicates that the computer and the LCD display panel are communicating. This LED will be ON when the computer is turned on and video signal is being generated. If the LED is ON and there is no image on the LCD display panel, the LCD display panel or inverter might be installed incorrectly or need replacement.

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Hey, that's great! You are very resourceful.

Hope you'll like it as much as I like mine, which I still use a lot every day. I highly recommend installing an SSD if you haven't already!

Definitely a bad NVIDIA GeForce 8800 GS. They are known to have issues along with most any other Nvidia based Mac (or PC) from 2007-2008, especially the 8600m in the MBP of that era. Bad solder was used that cracks over time from heating and cooling.

As you've discovered, you can "fix" it for a while by reflowing the solder (melting it and getting rid of the cracks basically). I hate to say this though, but it's only a temporary fix and the issue will crop back up later. The only way to completely fix it is to put a different video card in it such as the ATI 2600 Pro, or another 8800 GS that will ultimately fail like the rest.

It's great as long as it's working, and there are places out there that will actually go through the card and completely re solder it with better solder. It's not cheap, but it's a fix that should last.

Personally I'd try and stay away from Nvidia based Macs from that era, but seeing as you already have it. You can keep baking or using a heat gun on the video card for a while without loosing much, other than time. Or find a replacement. I'd go for replacing the card or getting a newer Mac with a good one. 2009+ Macs are pretty good, with the exception being anything made in 2011 using ATI cards. They have the same issue. 15" MBP and 27" iMac mostly.

uneo said:

Thanks alot for your reply, i have solved the problem. I baked the videocard for 10 mins and cleaned heatsink and fans which was the most dirtiest ive seen. That was all i did and it works very nice #

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Hello,
I have the exact same problem as you, and I'm planning on baking it sometime this week, can you please tell me if your mac is still working fine and that you didn't have to repeat the process since?
Also any tips on doing this??
Thanks,
Lucas