Shortly after the initial launch of the 7900GT CO/KO/Superclock series, a trend of hardware instability became more and more prevalent. Some symptoms of the unusually large number of defective cards include: artifacting while rendering graphics in graphics benchmarks such as 3DMark03, 3DMark05, 3DMark06 (all programmed by Futuremark, Inc.) Futuremark and Aquamark3, artifacting while playing games, BSODs (blue screens of death), total system restarts, and blinking screen.
A large batch of the 7900GT XX (note: XX may signify CO/KO/SC variants of the 7900GT) are believed to have defective and/or malfunctioning memory modules, thus causing instability and ultimately, total card failure. Another proposed cause of large-scale instability among the 7900GT XX include undervolting from the factory. That is, the 7900GT XX run at a 1.2 volt GPU core voltage, while their higher end relatives, the 7900GTX, have 1.4 volt GPU voltages, thus permitting higher clock frequencies (GPU/RAM). The 1.2 core volt coupled with factory clocks of up to 520/770 (1540 effective) may suggest that the core voltage is simply too low to allow for higher clock speeds. Another point to note is that the 7900GT XX and the 7900GTX are both based around the exact same core, featuring a 90nm process, allowing for a smaller die size and fewer total transistors within the core itself; it now becomes apparent that the 7900GT XX are actually meant to run at 1.4 volts, much like the 7900GTX, but are factory undervolted to 1.2 volts, for whatever reason nVidia may propose for doing this.
A term dubbed by myself and another fellow, known as the 'Fourth Day Syndrome' is in reference to the fact that many nVidia patrons who have purchased a 7900GT XX from a sub-manufacturer such as eVGA have frequently run into the aforementioned hardware failures synonymous with a significant number of 7900GT XX after the fourth day of using the card itself. The Fourth Day Syndrome itself is very likely a mere coincidence, but it may be a trend within a subset of the defective cards; something triggers massive card failure after four days, for an unknown reason. Recent speculation has determined the this Fourth Day Syndrome is most likely a continuation of the batch of 7900GTs with defective RAM. This batch first apeared with stock clocks of 520/1540, however the current KOs are clocked at 500/1500.
We believe that nVidia decided to downclock the core and RAM so that the problems with the defective RAM would propogate less often in the average user (who leaves their system at stock clock speeds). We are assuming of course that nVidia and its subcontractors are working to resolve this problem, and the future revisions of the card should be free of any defects. Currently, cards containing BIOS revisions up to 05.71.22.14.15 have had confirmed instances of Fourth Day Syndrome. Also note that even though this trend is common in enthusiast groups (such as EOCF), the actual number of defective GPUs makes up somewhere between five and ten precent of total 7900GT sales, based on RMA numbers.
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