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Strange system behavior in G5s tied to bad RAM System
I just purchased two PowerMac G5 2.0 GHz DP machines, each with the default 512 MB of RAM. I purchased aftermarket RAM to save some money over Apple's prices. Hopefully this story will save someone some hours of OS X troubleshooting work...

One of the machines has 5 GB and the other 8 GB. As part of a burn-in process, I ran two setiathome jobs on each machine. One machine was fine, but the other (8 GB) machine would hang after a while (5 - 30 minutes) under load. Worse yet, one or more sets of fans would go into "turbo mode" (very loud) and would need to be unplugged to stop. No system / console log entries were made regarding the problem.

All sticks of RAM were registered properly in System Profiler, and when idling or under light load there was no problem.

I had two brands of RAM (Edge and OWC) and initially thought that the combination might be a problem (it was not). I then went through an extensive troubleshooting effort and isolated the bad RAM to a single pair. The funny thing was that once I got down to a single bad pair the machine would finally panic before it hung. It did not panic when there were multiple pair of RAM.

Read the rest of the hint for more on the troubleshooting and repair process...

The AppleCare people seemed unaware of this type of problem. The seemed especially disinterested when I mentioned the "setiathome stress test" (although we routinely use this to burn-in equipment and it often finds problems).

The other thing that I found caused the fans to go into turbo mode was if the processor fans were not completely seated (this happened once on the 5 GB machine). The plate that the fans slide into is somewhat flimsy. The machine started fine but there was a red light visible at the front of the machine (near the power switch) and the fans were again very loud. And again, no system / console log entries were made and the machine ran fine for the few minutes that I was troubleshooting it. After reseating the fan it was fine.

Hopefully this information will save someone time (or a trip to the Genius Bar).

If anyone cares, the G5 processes a setiathome work unit in roughly 60-65 minutes per work unit (per processor, I run 2 jobs at once). My P4 1.9 GHz machine averages around 1.5 hours. Not bad.
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Strange system behavior in G5s tied to bad RAM
Authored by: jervidalo on Dec 03, '03 11:19:03AM

Ehh... 1.9 GHz G4??? That's new :)



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Strange system behavior in G5s tied to bad RAM
Authored by: jervidalo on Dec 03, '03 11:20:24AM

Ohh... My fault... P4... Not G4... Me being stupid here...



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Strange system behavior in G5s tied to bad RAM
Authored by: hadrienlc on Dec 03, '03 12:28:55PM

Make sure your RAM serial numbers are not HYMD232646-A8J-D43-AA-A

I had a similar problem due to apple's ram on a g5 1.8Ghz. They replaced it within a week and said that this problem only occurs if you install more RAM (512Mo for me).

My G5 runs now very well with 1G of RAM.



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Forget seti@home... use Folding@home
Authored by: Lectrick on Dec 03, '03 03:36:49PM
Use folding@home. Help find a cure for cancer. Chances are, the aliens are probably already here, so you're wasting your CPU on something frivolous. ;) A cure for cancer is a more humanistic goal.

(I had a good friend and two people with him see something very very odd, and close, in the sky, when he was 12. I had to drag the story out of him. He drew pictures at the time and showed them to me a couple of years ago. It certainly biased me a little in these matters, I guess... but look at it this way- if "they" are thousands of light years away, we can't do anything about it, and if "they" are already here, we can't do anything about it either. BUT we CAN maybe do something about cancer. Think about it.)

---
In /dev/null, no one can hear you scream

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Strange system behavior in G5s tied to bad RAM
Authored by: artychim on Dec 03, '03 05:07:38PM

Got the same story with our brand new PowerMac G5 2.0 GHz DP filled with 2 Go extra ram. It took a while to understand panics or supersonic behaviors before I had the idea to test memory with the provided DVD. Everything went OK with a new 512 Mo stick. Not obvious either to locate the guilty one !



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Strange system behavior in G5s tied to bad RAM
Authored by: ghlbtsk on Dec 04, '03 07:57:35AM

I have a 1.25 Ghz DP G4, and I ordered two gigs of OWC RAM when I got the machine. None of it worked anywhere other than the first slot, and none of it worked when there was more than one stick installed. This happened with two separate sets of four modules each (they replaced the first four with a new batch). It wasn't until they sent me TechWorks stuff that all was well. I still don't know what's going on with that company's RAM, but OWC doesn't seem to have a good track record here.



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Reliable tool to test RAM?
Authored by: elmimmo on Dec 05, '03 11:14:03AM

Does anyone know any reliable tool to test RAM in Macs, like what Memtest86 is for PCs?



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