Upgrade iMac 27" late 2009 video card?

Actually, the posts that state it can't be done are WRONG! And it does NOT require

any soldering or chip removal for the 27" iMacs.

I have the exact same late 2009 27" iMac, and upgraded it to the part from

OWC the you pointed out previously, this one:

http://eshop.macsales.com/item/Apple/6615578/

You'll be voiding your warranty certainly, but unless you have Apple care you're already

past Apple's 1yr anyway...

It is absolutely possible, and works great. You do not need to touch any firmware, and OS X

already has the drivers for this board. It's entirely a hardware process to upgrade it, i.e. open

the iMac and replace the board and you're done.

The process of upgrading it isn't particularly trivial, but it is absolutely possible, I've been using

the upgraded 5750 1GB board since last Fall (~October) without a single problem in my 27"

High level summary of steps, (there are better more detailed instructions a few places online like iFixit)

(1) remove display cover panel

(2) remove display itself, look online for the details this part can be dicey

(3) disconnect all cables from logic board, tape back near where they came from to get them out of the way and make them easy to reconnect

(4) remove RAM (makes it easier to remove logic board from housing)

(5) unscrew and remove logic board (which has MXM slotted video board attached to it)

(6) set logic board flat on a static safe area

(7) unscrew MXM video board heat sink screws that connect it to logic board, and disconnect it from the logic board

(8) plug in the upgrade/replacement video board

(9) put everything back together

(10) enjoy your faster video card

If you haven't taken your iMac apart before, expect to spend ~90min if you're careful about everything.

If you have, it can be done in ~30-45min.

A couple additional tips, one above was the removing RAM makes it easier to remove the logic board, another

is that when you reinsert the logic board, have a USB cable or similar handy to plug into the back to help

align the logic board when you re-seat it. The last tip is the one about taping the wires back just above where

they get plugged in. I didn't do this the first time through, and one fell down and didn't get plugged back in on

re-assembly. I had to disassemble the whole thing again to dig it out and plug it back in...

Cheers