I’ve been fighting memory-related lockups and random wonkiness on a Dual 2.7 PowerMac G5 for the past few days. I first noticed random weirdness on this machine occuring soon after it began capturing HDV footage, this computer had previously only been used for DV editing.

I guess that the HDV capture was using more of the 2.5GB of installed memory than normal, and one of the not-oft-used DIMM’s had some issues. To make matters all the more lovely, one of these DRAM-related unscheduled SUDDEN reboots also caused some hard disk corruption on the System drive. Joy.

Hopefully the steps that I went through to resolve the issues will prove helpful to some poor Apple-based editor. Read on…

I wasn’t sure if the System hard disk errors were the real cause of the lockups, so I decided to tackle them first. Disk Utility would not complete a “Repair Disk” function, even after booting from the Install Disk. It kept reporting “The underlying task reported failure on exit”. Not the most helpful error message, but what do I know…

So after some digging, I discovered a solution that worked. Per Apple’s fsck instructions, I booted into single user mode and ran the “/sbin/fsck/ -fy” command a few times (till fsck reported no errors).

With the hard drive successfully repaired, I then used Rember to check the G5 memory DIMMs for errors, and then narrowed down which physical DIMM it was with the Apple Hardware Test. Rember is a handy gui frontend to memtest, and it detects the bad DIMM(s) very quickly. The only snag is, it won’t tell you which one it is though. At least I couldn’t figure it out by reading the log…

The good news is that the Apple Hardware Test will tell you the DIMM number that fails the test (DIMM5 in my case). FYI, the DIMMS are numbered in pairs, from top to bottom, counting from the inside out. It’s simple, but sounds hard, here’s a ASCII diagram that will hopefully confuse you thoroughly:

7 =———-= 4
5 =———-= 3
3 =———-= 2
1 =———-= 1

2 =———-= 1
4 =———-= 2
6 =———-= 3
8 =———-= 4

The numbers on the left are the actual DIMM numbers as reported by the Hardware Test. The numbers on the right side of each DIMM are what you can physically see printed on the motherboard (when looking at the motherboard with the front of the case pointing to your left). The numbers on the right side don’t seem to mean much of anything except perhaps serving as a reminder to install matched pairs of memory.

The happy ending is that OWC (macsales.com) is going to replace the faulty memory DIMM, thanks to that handy lifetime warranty. Their warranty RMA process is quick and painless, and customer service is professional and responsive.

Notes:
FYI the Mac startup keyboard shortcuts I can never seem to remember are (after the “ding”):
*Hold down SHIFT to boot in Safe Mode.
*Hold down OPTION with the OSX Install DVD in the drive to choose a startup disk or run the Apple Hardware Test.
*Hold down COMMAND+S to boot in single user mode or COMMAND+V for verbose boot mode.