ATI x1600 problem almost fixed!

Question

Hello there,
As you already know, there are frequent display artifact problems and in general GPU stability problems with iMac (and macbook pro!) models featuring the notorious ATI x1600.
My last attempt at fixing this problem was to check the GPU diode temperature, which was around 59 degrees Celcius. The video card stability tests that I made showed beyond doubt that graphics chip stability was compromised at this temperature. One program showed random video RAM errors suggesting GPU bus instability, and the other program found artifacts in under 10 seconds.
Therefore, I downloaded the wonderful freeware program called smcFanControl and adjusted the minimum fan speed to about first 2000 rpm and then 1500 rpm, yes there is more noise, but the GPU Diode temperature is about 44 degrees now and there haven't been any nasty crashes for a while, and on the boot camp the video card stability surpassed the one minute mark. And I haven't seen any crashes since then, let's see how far it will go, it's past one day and there is no sign of a storm yet. I also keep the LCD brightness as low as possible (around median) to avoid excessive heat and do not use graphics intensive screensavers just to be on the safe side.
Hope this helps somebody around here!
Regards,
Eray Ozkural
Researcher, Erendiz Superbilgisayar Ltd.
PS: The Apple Hardware Test cannot find any fault when the GPU is malfunctioning....

Answer 1

The only difference is that people with problems tend to post on forums to state that they have problems. People who do not have problems generally do not have any reason to post that everything is perfectly fine. Therefore, such anecdotal evidence is heavy skewed to the negative.
Also, when I do a Google search on "ati x1600 mac," most of the hits are about people over-clocking their X1600 and how to do it (not about problems). Because they are able to over-clock from the stock settings, that tells me Apple designed a fairly large safety margin into the design, since any over-clocking will increase heat and decrease reliability. I have not personally over-clocked anything, since I am happy with the stock performance.
(I see no evidence to justify calling it "notorious.")
So my guess would be that I am not particularly lucky, but you may be unlucky. Or perhaps your iMac's cooling system is not working as well as it should, since you say that increasing the fan speed improves reliability; maybe airflow is being blocked or hindered internally or one of the fans is not working properly. Or your iMac's power supply is becoming faulty. Or you are plugging it into an old surge suppressor (power strip) or one with too many other devices connected (overloaded).