Graphics Memory Voltage Regulator Modification

After examining the memory voltage regulators, I raised the voltage of the internal circuitry and I/O buffers (VDD and VDDQ) by 0.2V. But overclocking was a complete disappointment. The maximum memory frequency the card could give out remained at the same: 950MHz (475MHz DDR).

Increasing the voltage by 0.2V more, I had a second try. It was the same: 950MHz.

I did everything I could think of – increased and decreased the voltage around the nominal, tried to vary VDD and VDDQ independently, then took the experiments over into the heat chamber and below-zero temperatures. Everything was in vain; the maximum frequency remained 950MHz.

At last, I gave up the idea of increasing the graphics memory voltage. It looks like 950MHz is the limit for the NVIDIA GeForce FX 5900 Ultra reference design and Hynix memory chips.

So, the card is ready for the tests:

We only have to replace the graphics chip and memory cooling solution with a more efficient one.

Redesigning the Cooling System for GeForce FX 5900 Ultra

The NVIDIA GeForce FX 5900 Ultra graphics chip has a copper casing. It is mounted on the die and protects it from chipping as well as distributes the heat along the surface of the heatsink. However, to get the best from overclocking, we’d better put off everything that’s in between the chip and the heatsink. So, I took the GPU casing off:

This operation was performed with a sharp paper knife. Those, who venture upon such an experiment despite the warranty, should better be VERY careful. The multi-layer wafer of the chip has “fragile” current-conducting paths that are too easily damaged with an unsteady hand.

So, here is the naked NVIDIA GeForce FX 5900 Ultra in person:

The white smudge in the screenshot is the thermal interface (KTP-8 paste) between the die and the water-unit. To take the heat off the GPU, I decided to use Thermaltake Aquarius II water-cooling solution. Because of the water-unit, I had to abandon the standard cooler, which had covered the memory chips, too. For the memory chips, I used heatsinks from an NVIDIA GeForce FX 5900 Ultra based card designed according to the reference.

The assembled system with the MSI card installed looked like this:

In order to push up the overclocking potential of the card, I took the system to a heat chamber that maintained a constant temperature of -15^oC throughout the tests.

So, MSI’s card featuring the NVIDIA GeForce FX 5900 Ultra GPU is ready for the tests. Now, we will try to make up a good competitor to it by modding a RADEON 9800 Pro based graphics card.