Sorry I havent replied to this thread but I'd probably be happy to jump on that offer and buy your old Card.
Would you email me at firstname.lastname@example.org to arrange details? (I dont see any kind of private messaging on this forum)
My 4850 fried (Green lines at apple grey screen, then checkered pattern when booting) so I took the opportunity to upgrade to a 6770.
The 6770 does not have the same size as the 4850 and the PCB holes for screws do not align with the motherboard, so only the heatsink screws are keeping everything in place.
Long story short, I rebooted, heard a chime, and ... black screen
I might have damaged the LED sync ribbon cable, but I have to report utter failure. Gutted, as I already performed the optibay/SSD hack with success 6 months ago.
Any tips on troubleshooting a blank screen?
Can I run the iMac headless and try to connect through SSH?
I think it should not be mixed with radiators MXM cards, each radiator is designed for its own PCB.
If you must replace the graphics card, then you must buy the complete PCB heatsink already brand-mounted, like this : http://applecomponents.com/items/661-5967_card-video-amd-radeon-hd-6770m-512mb/0 000005111?pn=1&s=661-5967&per_page=30
You should be sure that the model of the card are compatible with your 27" model.
Finally, it is very easy to "bad-pluging" the V-sync cable, it is very fine, it's best to have a one in rescue !!
Try to plug again correctly ...
Last time I had the same as you, gray screen boot => it was the V-sync cable.
If you want my HD4850 in good condition, i can sell you?
I live in France.
A very interesting thread…
Question, how it looks with a video card upgrade at early 2009 24” iMacs? According to my information they have also a second generation MXM slot, - so physically it should be possible. But I don’t know if there exist any version issues with EFI / vbios. Such an EFI version conflict was the reason for the incompatibility of the Radeon HD 2x00 series in polycarbonate 24” iMacs. (Physically they will fit perfectly because they have the same first generation MXM slot.)
However, if that all will work, - an other problem will be the heatsink. There was optional only available a radeon HD 4850 card, - is it possible to use a heatsink of that with a recent Radeon HD 6xxx card?
This is a very interesting topic, a nice piece of information indeed! Thank you everyone. I would like to ask you a question. Now I have an iMac 27" late 2009 intel core 2 duo(low end) with a 256Gb SSD and ATI HD4670 with 256 Mb. I am having slow and choppy animations with Mission Control since I updated to ML, so after checking everything (clean install and so all) I suppose upgrading my video card to an 512 Mb such as the ATI HD5670 (mid 2010) will do the trick.
Would I have any problem upgrading to this card? I suppose the shape of the card will be more similar to the 4670 than the 6970, isn't it? Would it be a noticeable difference in performance between the 5670 and the 4850? Does anyone want to sell me their 4850? I am from Spain.
Depends where you live. In USA there are plenty of sources, in Europe not so many.
I bought it here as I am in Europe:
Hello Teut, i'd seen your guide in the ifixit web and i'd found it very interesting. I'm thinking in doing the same with my Imac late 2009, but i'm worried about overheating. After a couple of months, is your system working well? No problem with that? Another question: you buy the video card at ThebookYard. Does it was a recycled piece? Thank you for your help.
No the card was brand new. And no heating issues IF you don't ruin the heat sensor cables in any way (which I did). If you experience loud fan noise which doesnt go away then you ripped of the heat sensor cable of the display. It can be fixed, but simply be careful when lifting up the display and disconnecting the cables.
As I said: no issues at all.