I have an iMac 27" mid-2011 with a semi-dead 6970M, 1gb GPU - I only got the system to boot by disabling the GPU kernel extensions(moving /System/Library/Extensions/AMD* to a backup location = weird and slow graphics, but better than just a gray screen) and Apple has refused to fix the problem because it's more than four years old - even though it's a recognized issue.
"I used one of the Dell / Alienware 2GB cards. These can still be got for under $200 on eBay. The Apple card is identical in every way except for the firmware.
This is the Dell / Alienware card here
Grab the Apple ROM file from here: https://www.techpowerup.com/vgabios/?arc... Pay attention to the VRAM size and get the correct file
Prepare the card by removing the Dell metal bracket that the heatsink screws into on the back of the card. You will need to transfer the bracket from the Apple card. Transfer anything else that might be needed.
On the card, with the MXM connector facing downwards and the ATI chip facing you. There are 2 small black chips to the top left of the ATI chip. (one above the other) You need to flash the top one as shown
You will need a way to interface with the chip on the card. I used a Raspberry Pi with a SOIC 8 clip.
Install Flashrom on the rPi. Use the guide here.
https://tomvanveen.eu/flashing-bios-chip...
Connect the rPi, the clip and plug it in. I have my Pi setup as an access point with its own Wifi network. This way, It is portable and can be run of a power bank
scp the file onto the pi. ""scp filename pi@ipaddress:/home/pi""
Backup the existing ROM first,
Flash the card and the card works perfectly as a genuine Apple card. I flashed the 1GB VBIOS version first before realising that I had the 2 GB card and had to dismantle the iMac again to reflash the card with the correct ROM. (I repeat, CHECK YOU HAVE THE CORRECT FILE)
After flashing the correct file it should look like this
You will get proper boot screen. No Kext hacking etc. The card works with full acceleration and passes Apple Service Diagnostics
Good luck and save yourselves a few quid.
Note, As this guide is now over 3 years old, time has marched on and not been kind to our 2009-2011 iMacs, The main issue we are all facing is the lack of Metal support with the AMD cards (If they haven’t failed already) As most of you are probably all aware, there are some great developers on the scene that have devoted a lot of time into keeping our old unsupported Macs on the road. Special credits must do to DosDude who created the Mojave and Catalina Patcher tools to allow people to run these operating systems on their older unsupported Macs.
Unfortunalty with these iMacs, It can be done but requires a more up to date graphics card. There are 2 cards that I have found which offer boot screen and Metal support. There is a size “B” card for the 27” iMacs and a size “A” card for the 21.5” Macs. The size “A” will work in both.
These of course need to be flashed before they will work correctly. If there is enough demand for this I may setup a store to sell pre flashed MXM cards for these systems. A guide will also be provided for those that wish to flash the cards themselves. I will edit the original post to bring it into the 20’s"
iMac (27-inch): AMD Radeon 6970M Video Card Replacement Program
Apple has determined that some AMD Radeon HD 6970M video cards used in 27-inch iMac computers with 3.1GHz quad-core Intel Core i5 or 3.4GHz quad-core Intel Core i7 processors may fail, causing the computer’s display to appear distorted, white or blue with vertical lines, or to turn black. iMac computers with affected video cards were sold between May 2011 and October 2012."
"Adding my experience here. I had a 2011 27 iMac’s GPU go bad with the pink vertical lines. I’m in rural South Korea, so there weren’t a lot of options.
I considered baking, but longevity was an issue. This discussion and others like it helped me along. I got this Dell/Alienware GPU from Ebay (below, Apple on the left; new card on the right, note the two silver squares that have “R22” printed on them … those are too high for the heatsink and it’s not a perfect fit) and installed that with iFixit instructions (although there are no instructions specifically for a GPU swap on this model, the dual-drive install instructions got me where I needed to go.
The card is the correct size, but two parts on the card were too tall and left a big gap when the heatsink was put back on (below).
I salvaged two copper squares from the heatsink of an Apple laptop and used them as spacers with a generous helpings of Arctic Silver between each layer.
After that, I screwed the heatsink on tightly. It sits a degree or two off-straight, but works fine (below).
I got everything back together and booted to a black screen and waited (remember, this is the result of no Apple ROM). It all worked perfectly once the iMac reached the login screen. I installed Brightness Slider to adjust the display brightness and it works well enough.
After about 3 hours, the iMac went to sleep and when I woke it back up, the right half of the screen was about 50% darker. On a dead cold boot (e.g. after the weekend), the screen was normal, but then after a short period, the right half of the screen would darken.
I could still see things and get work done, so I put up with this for a few weeks until I had time to deal with it. The iMac itself was running just fine. When I had time to open it and lift the LED, my diagnosis was confirmed: the display data cable was getting too hot. There is tape to prevent, but it was worn/melted slightly (below).
I used more parts salvaged from the laptop to raise the display data cable up more than it had been. You can see in Step 10 of these instructions how the foam is strong and probably does the job right, but mine computer wasn’t like that, it was smushed down quite a bit.
I salvaged tape and the foam from the laptop. I didn’t need it to do much other than keep the heat off of the cable. I assume that because the heatsink didn’t fit properly and I didn’t pack all the chips with thermal compound (I didn’t have any), that excess heat is coming off of the wrong side of the GPU. This is something to deal with later.
The cable got the height needed when I lowered the screen back down.
The iMac works flawlessly now. I’m running High Sierra with the CUDA and web drivers suggested in this post. I did not need to have the drivers installed before swapping the GPU cards. YMMV."
"Same $@$* here in Hungary. Apple don't care about customers even they paid a lot to buy the flagship of Apple. It's a shame, in this big company. VW, Toyota etc... called back all the cars, which they put wrong spares. Apple just give 4 extra years, even they proudly says, they know they put wrong sparepart to their most expensive product.
I don't know even why any lawyer doesn't see the business in this easy possibility to get a lot of money from Apple??? :) They &&^&@@ up us easily with a lot of money...
Is there anybody, who bought used Video board to fix it? I sent mine to repair to a specialist company to greece to reballing, but it wasn't help. They tried two times, but finally sent it back with the money. I found lot of used cards on different market sites, but i don't know, how will they work, how long... I don't trust Apple anymore. Now I have an 27"" Imac I7 8Gb Ram and cant't use. The complete, used, same, working Imac is 6-7-800 Euros, and used card is 300 euros..
"I've repaired a couple of Mac's by removing the videocard, stripping it from all thermal-fluid, plastic etc. Put in in the oven for 8-10 minutes at 200 degrees Celsius , and putting it back (using new thermal pasta). This will let the soldier melt a little bit so any short-circuits don't appear anymore causing the GPU to work again.
it's difficult and time-consuming but it beats replacing a GPU for a lot of $ (or € in my case :)
And some PC laptops have the exact same problems with the GPU. Sometimes the thermal pasta or copper heatsink won't be doing it's job right causing the GPU to get real hot and fail eventually. A lose connection with one of the chips is mostly the case (also from using environmental friendly soldier).."
