Channel exception error with NVIDIA card: Heat and GeForce card replacements

Posted by Pierre Igot in: Macintosh
August 31st, 2009 • 4:07 pm

I experienced my third channel exception error / GPU restart in 10 days last Friday (August 28). The symptoms were the same as with the previous one: The entire UI froze with no apparent reason while I was attempting to drag a message window in Mail in order to move it around. (It used to occur when I was opening PDF files in Preview. I guess the bug figured it was due for a change.)

There was initially a lot of hard drive activity that I could hear, but after a while the activity stopped, and the UI stayed entirely frozen, with the only moving part being the Spinning Beach Ball of Death.

As with the previous occurrence, I was able to log in remotely via ssh from my other Mac Pro and run the “sudo /usr/libexec/stackshot -it” command. I was also above to confirm, via the top command, that all my open processes were still running apparently just fine.

I then ran “sudo shutdown -r now” to force a restart of the frozen machine.

After that, I submitted the new stackshot logs to Apple. They still haven’t responded to my last bug report (the one with the first stackshot logs that I was able to send), so I just added the new information to the existing bug report. Based on what other people have told me, I am not too hopeful that I will ever get a response. It seems that Apple is in strong denial about the whole thing.

The one different aspect this time was that the weather was significantly different. The last two occurrences had taken place in a context of very warm, stuffy weather, which made me suspect that overheating might be playing a part. But this time the temperature had dropped significantly and the weather was pretty dry. So that seems to contradict earlier theories about the problem being possibly due to the graphics card overheating.

On the other hand, early reports on Snow Leopard seem to indicate that the problem has somehow vanished altogether (although that remains to be confirmed). I haven’t installed Snow Leopard on my machine yet, so I cannot yet verify this myself yet. If that were indeed the case, it would probably confirm that this particular bug is some kind of weird issue that involves both hardware and software issues. Maybe there is a flaw in the GeForce 7300 or in certain batches of GeForce 7300s that Snow Leopard is somehow able to work around.

I should also note that, following my last blog post on the topic, I received a tip from a source that I cannot name, saying:

Apple is now replacing NVIDIA GeForce 7300 GT cards in or out of warranty for certain computers that are experiencing video issues. The serial number is in the range of xx738xxxxxx or xx741xxxxxx to xx803xxxxxx, and either capacitor C77 or C79 is protruding. I would highly recommend trying to get the card replaced.

I cannot confirm whether there is such a replacement program in place. Given that my Mac Pro’s serial number starts with G8633, I am not sure how that would fit with the numbering scheme described in this post. In any case, it doesn’t look like I would qualify for that particular program anyway, if it does indeed exist.

I don’t have time to investigate this further at this point, especially since 1) the problem only occurs intermittently on my machine (three times in 14 days now) and 2) Snow Leopard might fix it. The next big test for me will be to install Snow Leopard.

In the mean time, however, in light of this tip indicating that there might be something wrong with a particular batch of GeForce 7300 cards, I did decide to try something else and replace my Mac Pro’s GeForce 7300 card with the one from my other Mac Pro, which I was not using anymore since I got a GeForce 8800 for that other machine. The other Mac Pro is about the same age as my main machine, so I am not sure it will make much difference, but it is worth a try, just in case.

I did the graphics card swap on Saturday morning (August 29) and so far, so good. But of course it’s far too early to draw any conclusions.

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