VR-Zone's resident hardcore overclocker, Shamino. has thrown up a new Guide to Modding your GeForce 6800 Ultra voltage through resistor or a humble pencil to improve overclockability!
Look for the chip at the back of the card as shown. You can measure the voltage of your 6800 ultra from the point shown below. Without drivers loaded it should be around 1.13v with drivers loaded it should be 1.43v. To increase voltage, you can solder a 100K variable resistor to the point shown. Set the VR to the max 100k ohms first. Ground the other end of the VR. This will give you around 0.24v more, so 1.37v without drivers and 1.67v with drivers. There is overvoltage protection on the card so that as you turn down the VR, there will be a point whereby it will drop voltage and throttle with lines on screen. My card is insulated at the moment so I have no chance to check for any workarounds.
NVIDIA GeForce 6800 Ultra Voltage Mod with Pencil
Look for the chip at the back of the card as shown. You can measure the voltage of your 6800 ultra from the point shown below. Without drivers loaded it should be around 1.13v with drivers loaded it should be 1.43v. To increase voltage, you can solder a 100K variable resistor to the point shown. Set the VR to the max 100k ohms first. Ground the other end of the VR. This will give you around 0.24v more, so 1.37v without drivers and 1.67v with drivers. There is overvoltage protection on the card so that as you turn down the VR, there will be a point whereby it will drop voltage and throttle with lines on screen. My card is insulated at the moment so I have no chance to check for any workarounds.
NVIDIA GeForce 6800 Ultra Voltage Mod with Pencil
