I will slowly bump this little threda with my attempts of overclocking old and rusty geforce video card.
So here is the patient. It is a Geforce 8600gt with 512 Mbs of video memory. Default clocks are 540 MHz for GPU, 400 MHz for RAM. On attached picture you can see the videocard itself. I outlined most important parts. There is GPU chip, 8 memory chips, two phases of Voltage Regulator Module (VRM) for GPU and one VRM phase for memory as it consumes less power than GPU. And the voltage controller which is most important for us.
I have already tried overlocking it from OS with default voltage and failed horribly. All I got was 600 MHz for GPU and 430 MHz for memory which isn't enough for me. As I read this card can achieve 1000 MHz! after voltmod, so I grabbed my soldering iron and started looking into datasheets of voltage controller which can be seen on second picture. It is a RT9259A. This is controller responsible for regulating voltage to GPU. Memory's voltage controller is on other side of videocard, we will comeback to it later. Now we have to find two important legs(pins) of this controller which will help us to control output voltage to GPU. First leg is FB which means FeedBack. What does it do?
Here is quote from datasheet.
>Buck converter feedback voltage. This pin is the inverting input of the PWM error amplifier. FB senses the switcher output through an external resistor divider network.
Basically it senses resistance and outputs necessary voltage based on this resistance. How do we change resistance? As we know from school classes, adding more resistance won't do anything cause electricity looking for easiest path. So we lower it. How do we lower it? We solder resistor with less resistance(Ohms) between FB and GROUND ( which is our second leg) so now electricity will find even easier way to flow!