Input/Output circuitry (VDDQ) is powered by another regulator, based on ISL6225CA chip, which was specifically designed for memory voltage regulators. The output voltage for each channel of this dual-channel regulator is determined by the ratio of resistances in the feedback circuit. This is a simplified scheme of the chip:

The output voltage is determined by the formula: V=0.9*(1+R1/R2). We can increase it by reducing R2 resistance (marked with a red circle in the scheme above). Having found the necessary resistor on the PCB, I attached an additional 4.7kOhm resistor in parallel to it:

As a result, the voltage of the I/O circuitry increased from 2.53V to 2.88V. Now that the microsurgery has been done, I can start overclocking the thing.

We had more luck with this graphics card: 600MHz graphics core and 1010MHz memory frequencies are good, since without volt-modding the GPU was only stable at 515MHz. Memory frequency gain was only 10MHz, but this fact has a simple explanation – the memory chips reached their frequency ceiling.

Testbed Configuration and Methods

The testbed was configured as follows:

• AMD Athlon XP 3200+ CPU (2.20GHz, 400MHz FSB, 512KB L2 cache);
• ABIT NF7-S mainboard v.2.0;
• 2x256MB Corsair XMS PC3200 (2-3-3-6 timings);
• Seagate Barracuda 7200.7 HDD (Serial ATA-150 interface);
• NVIDIA MCP-T audio;
• Microsoft Windows XP SP1, DirectX 9.0b;
• Drivers: nForce Unified Driver Pack 3.13, ATI Catalyst 3.9, NVIDIA ForceWare 52.16.

We tested the graphics cards in the following operational modes:

• Regular frequencies;
• Overdrive (for the RADEON 9800 XT only);
• Ordinary overclocking (without volt-modding);
• Extreme overclocking (with volt-modding).

We used the following benchmarking games and applications:

First-person 3D shooter:

• Return to Castle Wolfenstein: Enemy Territory;
• Star Trek Elite Force 2;
• Unreal Tournament 2003;
• Halo: Combat Evolved;
• Tron 2.0.

Third-person 3D shooter:

• Tom Clancy’s Splinter Cell;
• Tomb Raider: Angel of Darkness.

Simulators:

• F1 Challenge 99-2002;
• IL-2 Sturmovik: Forgotten Battles.

Real-time strategy games:

• Command & Conquer: Generals – Zero Hour.

Semi-synthetic benchmarks:

• AquaMark3;
• Final Fantasy XI Official Benchmark 2;
• X2 – The Threat Rolling Demo.

Synthetic benchmarks:

• Futuremark 3DMark03 build 340.