Before we started on the voltage modification, we picked out a the measuring points for the GPU voltage. In this case, Vgpu can be read off the highlighted end of the inductor in the “SMPS A676-00 TILE” area. The reading is taken with respect to ground.

vrmgpu Voltage Modification Guide For Sapphire X1600PRO 256MB

The default Vgpu hovers around 1.38V.

Flip to the back of the card where the voltage modification is carried out. You will see a PWM Buck Regulator going by the part number of RT9232.

 Voltage Modification Guide For Sapphire X1600PRO 256MB

Hook a 10kOHM variable resistor between pin 5 and ground. Starting with the resistance set at maximum, decrease the resistance slowly for Vgpu to rise.