Extreme Overclocking of GeForce 9800 GTX: Methods and Results
It is simple to modify the GPU power circuit on the GeForce 9800 GTX. It uses the same controller as the GeForce 8800 GT/GTS, i.e. the Primarion PX3544 chip. What makes it even easier is that the components are placed in the same way. So, the modification is performed by connecting Pin 19 of the PX3544 chip with the ground via a trimming 1,000Ohm resistor.
A multiturn precision resistor is desired for accurate adjustment of the GPU voltage. The PX3544 has very small leads you can hardly solder anything to, so the most convenient point for connecting the resistor is marked with a red dot in the photo below. The best way to read the current voltage is from the row of ceramic capacitors located in the GPU zone on the reverse side of the PCB. You can use any of them. Here, the C666 capacitor, marked with a red dot, is employed.
We did not disable the overvoltage and overcurrent protection of the GPU because this would have increased the risk of damaging the card in the process of overclocking. We didn’t volt-mod the memory circuitry because the Anpec APW7066-based circuit required separate modifications for VDD and VDDQ voltages. It just didn’t seem worth the trouble as we didn’t expect high results from memory overclocking. The goal of this review is to pit the modified GeForce 9800 GTX against ATI’s new solutions but the memory frequency of the Radeon HD 4850 is a modest 2GHz whereas the Radeon HD 4870 with its 3.6GHz GDDR5 memory is obviously unrivalled in this respect. Moreover, the accelerated version of GeForce 9800 GTX (with the plus sign in its name) doesn’t use overclocked memory. It comes with a memory frequency of 1100 (2200) MHz in both versions.
When the driver is loaded, the default GPU frequency is 1.22V in 3D mode. Having increased it to 1.528V we watched the card pass all of our tests at GPU frequencies of 875/2188MHz (879/2214MHz as reported by RivaTuner). This is an achievement: a frequency growth of 200MHz for the main domain of the G92 core and 500MHz for the shader domain The protection system woke up when we tried to increase the GPU voltage further, so we stopped at that. We didn’t want to ruin the card after all – we wanted to benchmark it.
For the card not to overheat we set its cooler’s fan at maximum speed. That was not easy for the ears, of course. Surprisingly, the temperature of the overclocked card’s core was only 50°C in idle mode and 85-87°C under load. The developer should be given credit for creating what is perhaps the best reference cooler for modern graphics cards.