GPU Voltage Regulator Modification

As it turns out, it is only necessary to change a part of the driver’s code to increase the voltage in the 3D mode, or program the regulator itself. I guess we will soon see utilities that allow adjusting the voltage of GeForce FX 5900/5900 Ultra based cards. For now, I have to look for a hardware way: I’m not too much into writing drivers to make such a utility myself. :)

The card’s voltage regulator suits perfectly for an external intervention: the ISL6569 chip has a special OFS input, connected to the current source and a divisor. By connecting a resistor between the OFS input and the common wire, it is possible to increase the output voltage of the regulator above what is set by the binary code at the DAC input:

The voltage offset value when a resistor with resistance of R is connected equals (100µA*R)/10.

The OFS output of the ISL6569 chip is connected in the MSI card with the common wire through a chain of resistors with zero resistance. Thus, it is easy to increase the voltage by simply substituting one of the links with a resistor with the desired resistance. I soldered wires instead of the resistor for better convenience:

And then soldered a variable resistor (with 33kOhm nominal) to the ends of the wires:

During extreme overclocking experiments, I found acceptable a resistance of 30kOhm. Thus, the GPU voltage in the 3D mode was 1.69V, that is, it grew 0.29V higher.

You should keep in mind that the voltage offset doesn’t depend on the input data sent to the DAC of ISL6569. That is, the GPU voltage is increased in all operational modes. Accordingly, the heat dissipation increases calling for better cooling of the graphics processor.

We will deal with cooling and overclocking a bit later. Right now, let me complain to you about my memory overclocking experience.