27-inch iMac Graphics Firmware Update 1.0
Apple has released a much-needed firmware update for the 27-inch iMac that aims to address that model’s widespread display problems. The update is for the ATI Radeon HD 4670 and 4850 graphics cards, and corrects issues causing “image corruption or display flickering.” Those issues have been widely discussed in Apple’s Support Discussion forums (see “New iMac Screens Cracking and Flickering,” 10 December 2009) in conjunction with instances of shipped iMacs arriving with cracked screens – still no word on that latter problem. Finally, take heed of this important warning in Apple’s release notes, “Do not disturb or shut off the power on your
iMac during this update. Loss of power could result in your iMac failing to start up.” The update is available via Software Update and the Apple Support Downloads page. (Free, 683 KB)
Well, it doesn't seem to have worked perfectly. I got my new 27" iMac with the high-end graphics card, and mostly it works fine, with a stunning screen image. However, a couple of times I've had the dreaded flicker effect...although I'd liken it more to a full-blown seizure, with big lightning-like zaps across the screen, followed by the bottom inch of the image flipping up to the top of the screen, and full blackouts for a second or two. It's only happened twice in two weeks, both times when either viewing or having just viewed a Flash movie or Flash Facebook animation in Safari (possibly coincidental, of course, but that's what I was doing both times). I suppose if it happens again I'll have to haul the machine to the Apple Store...a pain, since it's all nicely configured and all.
I've had my 27in with the HD4850 card too for about one week now with the same symptoms. Except mine happens every day. Once I reboot, the issue is fine...until the next day. Going to take it to the Apple Store but not confident a replacement won't have the same problem.