GeForce 8800 GS/GT/GTS Voltmods
GPU Voltage Mod
Locate the chip labeled "Primarion PX3544" on the backside of the card. Solder a wire on the middle pin and another one on one of the outer pins of a 500 Ω variable resistor. I personally like to use those pins that make resistance decrease when the tuning screw of the VR is turned clockwise consequently increasing voltage. Cut or insulate the 3rd, unused pin. Use the resistance measuring mode of your digital multimeter and tune the VR to maximum resistance (very important!). You may want to write down on a piece of paper which way you need to turn the tuning screw in order to decrease resistance. Solder the free ends of the wires on the pads as depicted in the instruction picture above.
Tune down the resistance slowly to increase voltage. Don't be worried if the first few rotations don't seem make any difference, this is normal. The more rotations you turn the faster vGPU increses - so tread carefully.
Always monitor the resulting vGPU with your multimeter while tuning. Red probe to the point marked with a green arrow labeled as "vGPU" (see paragraph: Overview), black probe into a ground (Molex connector, eg.). Default vGPU voltage for the GeForce 8800 GT is ~1.10 V under 3D load. 33% overvolt (1.463 V under load) should be enough for maxing out the GPU under conventional cooling methods. Note that vGPU increases spontaneously by ~0.05 V when entering 3D load.
Higher vGPU voltages can cause the heat output and temperature of the GPU chip and the voltage converter circuit to increase dramatically. Make sure you provide adequate cooling on the whole card when overvolted and overclocked.