Important article directly from G5 users forum


Are you experiencing intermittent freezes and/or kernel panics? Well, below we have put together a 12-step diagnostic program to help you isolate your problem. It's modeled after the Alcoholics Anonymous 12-step program, only when you get done with ours and your G5 still does not work, you have our permission to start drinking. Nyuk, Nyuk, Nyuk.   Smile  

Serious though folks, intermittent problems can be very difficult and time consuming to pinpoint. You need to be very patient. It may take you days or even a few weeks to find the root of the problem. The key is to methodically attack the problem step-by-step and then run the computer for an extended period of time after each step.  

Before you start, we suggest you use Carbon Copy Cloner or CloneX and clone your hard drive to another drive for backup. Now, grab a beverage and let's get started.

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Troubleshooting Intermittent Freezes and/or Kernel Panics  

Step 1: Do simple maintenance first. Run Disk First Aid from your install CD to check drive and repair permissions. Use a utility like Xupport , Cocktail or Onyx to clean user/system cache, logs, memory swap files, etc. We would also suggest using DiskWarrior or Tech Tool Pro 4 to rebuild directories.

Step 2: Disconnect any external devices except mouse and keyboard. Try a different keyboard and/or mouse if you have one. Also, you might try hooking up another monitor if you have one.

Step 3: Pull your stock RAM out and reseat it. Remove any third-party RAM you installed. Just use the RAM that came with computer or install new "known good" RAM.

Step 4: Pull your video card out and reseat it.

Step 5: Run your hardware tester that came with your computer on extended mode. If all checks ok, proceed to next step.

Step 6: Reset your PMU and NVRAM.

Step 7: Create another User account and run computer under that user. This will help determine if the problem is software related and localized to your Home (Library) folder or your root System.

Step 8: Start and run computer in Safe Mode . This is equivalent to running OS 9 with extensions turned off.

Step 9: Do an Archive and Install. Run the computer for an extended period of time without adding anything back from your Previous System folder.

Step 10: Reformat your drive using "Zero all data" option with your Disk Utility and install a fresh OS X off your install disk.

Step 11: Reinstall your applications one at a time.

Step 12: If you're still experiencing problems after going through the steps above, at this point, your video card, logic board and/or processor(s) may need to be replaced. Take unit to an Apple Service Center. NOTE: You can contact Apple and see if they will send you a video card to try. It's a user serviceable part.

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UPDATE: Apple engineers have reported that some freezes may be caused by Quartz Extreme and suggest disabling it s a temporary fix.

To disable Quartz Extreme, enter the following command in Terminal:
defaults write /Library/Preferences/com.apple.windowserver GLCompositor -dict tileHeight -int 0 tileWidth -int 0

To re-enable Quartz Extreme, enter the following command in Terminal:
defaults delete /Library/Preferences/com.apple.windowserver GLCompositor

You can also downlaod this app to disable Quartz Extreme.

http://developer.apple.com/qa/qa2001/downloads/qa1236_1.tar.gz