I got my iMac G5 almost six months ago, and it worked perfectly until two days ago. It started occasionally hanging for 2-3 seconds with “snowy” video, and would then go back to normal. A complete reformat/reinstall didn’t solve the problem, and I started seeing a lot of these in the system.log:
Feb 28 04:11:05 coldshot kernel: Graphics chip error! Restarted.
Feb 28 04:13:54 coldshot kernel: Graphics chip error! Restarted.
Feb 28 04:49:46 coldshot kernel: Graphics chip error! Restarted.
Feb 28 05:03:22 coldshot kernel: Graphics chip error! Restarted.
Feb 28 05:12:38 coldshot kernel: Graphics chip error! Restarted.
Running the Apple Hardware Test CD resulted in a diagnosis of bad VRAM (built into the system board). This morning I called AppleCare, and I should have a replacement “midplane” (motherboard) here within five days, along with installation instructions.