I bought a 2010 27 inch iMac with an i3 CPU a few months ago at a reasonably good price on Craigslist, intending to add an SSD and upgrade the CPU to an i7. I went to a local computer shop looking for an i7, and while I was standing in line someone brought out from the back a 27 inch iMac, presumably in for repairs, and handed it over the counter to the iMac owner, telling him that they couldn't fix the iMac. I asked the iMac owner what was the problem, and he said, unhappily, that the video card had failed. [Note that the computer store had already removed the internal hard drive, so his data--he was a video developer--was safe and secure in his hands.]
I told the iMac owner I was in the store right now looking for a used i7 for a 2010 iMac, and asked him if his iMac was a 2010, and if it had an i7. He said yes, and I asked him if he wanted to sell it. He said sure, it's no good to me now. Neither of us knew what it was worth, so I said, Look, I only need the CPU, and offered him $20 (Canadian). He said OK, and asked me if I wanted to buy the RAM also, 4x4GB=16GB. I asked him how much, he didn't know, but the computer store employee said $80 for the RAM was reasonable. I didn't have the cash on me, so we walked to my bank and I paid him $100.
I got home, the 2010 iMac was already apart, waiting for me to install the SSD. I disassembled the new iMac I had just bought, intending to take out the i7. After I got it apart, I realized that the new iMac was not a 2010 Mac at all, but rather a 2011. "Damn" I thought, now I have an iMac with a fried video card. But at least I bought the 16GB RAM at a reasonable price for used RAM.
Then I got to thinking, wondering how much it would cost to replace the fried video card. I checked eBay, and WOW!!! it was $900 Canadian for a new video card for a 2010 iMac. Unfortunately that was at least ten times more than I wanted to pay. I started scrolling through eBay, looking at prices for video cards and came upon an ad claiming to fix a video card for a 2010 iMac for $119, 3-5 days turnaround, 90 day guarantee. (You had to remove the video card yourself, and mail it to the vendor). That seemed like a pretty good deal, so I emailed the eBay vendor to see if this also applied to a 2011 iMac. "Sure, no problem with a 2011 iMac", the vendor said.
An hour or so later I started thinking again, how could someone "fix" a fried video card, guaranteed, with a turnaround of less than a week? How can you "fix" a video card, with ten zillion connections?
All of a sudden, some neglected, long forgotten sectors in the back of my brain fired, and then it struck me; I googled "iMac 27 inch video card oven".
The following video turned up:
It's a long video, but essentially a really nice, believable guy named Evan, from Greece I think, explains in some detail how he fixed a failed video card on his 2011 iMac by putting it in the oven for 8 minutes at 200 degrees Celsius (405 degrees F.). It seemed ridiculous, but since I had both iMacs apart, I thought WTF, I've got nothing to lose, why not give it a try?
So I got started. I must admit though, after a lot of painstaking work disassembling the logic board, and then extracting the video card, I felt pretty stupid for a few minutes when I got to the point of actually putting the video card in the oven.
After installing an SSD I had lying around and completely re-assembling the 2011 iMac (nearly a full and very gruelling day!), and starting it up, I waited for twenty or thirty seconds...
And then, I couldn't believe it. The friggin' iMac started right up and the video card was, magically, no longer fried!!!
That was like two months ago, and it's still going. I'm writing this on my salvaged 2011 iMac right now. I have since then installed a 250GB SSD with velcro tape under the optical drive, replaced the original internal hard drive with a 2TB drive, attached a 30 inch Cinema Display monitor, upgraded the RAM to 24GB, and installed macOS High Sierra 10.13.1. I have a bunch of Mac Pros, MacBook Pros, MacBook Airs, iMacs, etc., of various vintages, plus more than a couple of older PCs, and according to Geekbench 4, this is the fastest computer I currently own, even beating both of my 8 core Mac Pros with dual Xeon processors.
Except that the GPU diode runs quite hot (according to Macs Fan Control nearly 80 degrees Ceisius, yikes!!!), my new $20 2011 27 inch iMac seems to be performing admirably.
Oh yeah, and I eventually found and upgraded the i3 to a compatible i7 ($119 from a local used computer dealer) in my first 2010 iMac, installed an SSD and a 2TB internal drive. The 2010 iMac was also successfully tested with 24GB of RAM.
I'm kind of delighted with all this. As you can probably tell.