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Voltage is monitored in a not very-easy-to-access point – on one of the “barrels” on the card’s face side. I recommend you solder a wire to the measurement point and hang the multimeter on this wire – this is much handier than grope for the necessary spot each time.

It is a distinguishing trait of many graphics cards of the NVIDIA GeForce FX series that they can dynamically control the core frequency. The graphics memory always works at the same clock rate, while the graphics chip has two basic operational modes: its frequency is 300MHz in 2D applications and increases in 3D applications (in our case, the frequency of the 5900XT GPU goes up to 390MHz). Besides that, the graphics core works at 250MHz only when the power connector is empty and at 376MHz when the auto-brake is applied (see the FAQ on NVIDIA GeForce FX 5900XT).

I don’t say it to impress you with my extensive knowledge of graphics cards, but only to lead you to another peculiarity of the 5900XT (and other GeForce FX chips as well).

The core voltage changes along with the frequency!

The values follow:

  • Starting voltage: 1.13V
  • 2D-mode voltage: 1.2V
  • Throttling voltage: 1.3V
  • 3D-mode voltage: 1.4V

This is very important when tweaking Vgpu. If you adjust the voltage in the 2D mode, always add 0.2v to the value on the multimeter! That is, if 1.85v is set in the 2D mode, the core switches to 2.05v on the start of any 3D application, which is not going to end well. Ok, you have had another warning, let’s move on…

As you must have noticed, the standard Vgpu of 5900XT graphics cards is 1.4v in the 3D mode, while the same voltage is 1.6v for the 5950 Ultra. Considering that the two cores have much in common, I’d say that 1.6v is the optimal point for people who don’t want to run any risks. In fact, the 5900XT core is supposed to work at 1.6v, but works at a reduced voltage. The average frequency gain above the standard Vgpu is 50MHz and this is quite enough for everyday work.

But of course we don’t stop at that. We increased the voltage to 1.95v, raising the chip frequency to 645MHz (as you remember, 390MHz is the nominal clock rate). The maximum frequency was 615MHz with 1.9v and 617MHz with 1.8v voltage.

The state of the graphics card:

  • Cooling – Koolance EXOS
  • Chip’s lid is removed

As you see, the card enjoys the growth of Vgpu till the limit, increasing the overclockability of the core. Why do I start talking about limits? You’ll learn closer to the end of the article. You should definitely read it through if you’re about to make the Vgpu volt-mod!

 
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