ATI Radeon 4850 graphics chipset lockup issue on new iMacs
Apple customers who have recently purchased a new, customized aluminum iMac containing the ATI Radeon HD 4850 graphics chip have been experiencing lockup issues. The issues surrounding the recent reports seem to duplicate reports from nearly two years ago
Apple Support Discussions forum user "Nic T" describes symptoms:
"Mouse does not move, keyboard does not respond to input. Pressed the power button for 5 seconds to shut down. Booted up in single user mode to repair HD, started up fine again, started to install my apps and move the files over from my previous iMac. Played movies on it, and it froze again. Mouse and keyboard do not respond to input, just a short 1 sec sound from the movie that kept looping.This happens a few times a day.
Got fed up, reinstalled the operating system again, zapped NVRAM, PRAM, Disk Utilities check, repaired permissions, started to play COD4. Just a couple of minutes into the game, the iMac froze again. Keyboard and mouse will not respond to input. Sound stutters."
Possible fixes
At this time, there does not seem to be a workaround or fix for this issue. Since this appears to be happening on newer models, we recommend contacting Apple and having the issues checked out by an authorized service technician or making a Genius Bar appointment and taking your machine to your local Apple Store.
From AppleInsider:
"None of the typical troubleshooting steps have an effect on the flaw, including resets for the PRAM or the SMC unit that are often used to diagnose hardware-only problems.Apple may already be aware of the issue. Some of those calling the company's support line have heard from technicians that there are numerous reports and that a fix is in the works, possibly arriving along with the looming Mac OS X 10.5.7 update. Some are being offered replacement systems after unsuccessful troubleshooting."
Resources
Read the AppleInsider Article reporting lock-up issues with new iMacs containing the ATI Radeon HD 4850 graphics chipset.
Read an Apple Support Discussion thread regarding the lock-up issues surrounding the ATI Radeon HD 4850 graphics chipset.
Read another Apple Support Discussion thread regarding the lock-up issues surrounding the ATI Radeon HD 4850 graphics chipset.
Read this Mac Rumors forum thread discussing the ATI Radeon 4850 lock-up issues.
Read this CNET Australia article from 2007 reporting iMac freezing issues caused by the graphics interface.
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Resources