X-bit labs

PowerColor RADEON X800 PRO Graphics Card: Modification, Extreme Overclocking and a Duel against Leadtek GeForce 6800 GT (page 2)

Category: Video

by Tim Tscheblockov

[ 07/15/2004 | 12:55 PM ]

In spite of the original packaging, the graphics card itself is a very ordinary RADEON X800 Pro, designed according to the reference etalon; they only glued another sticker on the cooler, on top of ATI’s own picture:

The cooler’s heatsink consists of two parts: a thick copper base that takes heat away from the GPU, and a copper “accordion” that’s attached to this base with heat-conductive glue. The whole contraption is covered with a plastic casing, which directs the air stream along the heatsink ribs. The memory chips, like on ATI’s reference boards, have no special cooling. The PowerColor card is equipped with 256MB of GDDR3 – the 2ns chips are manufactured by Samsung.

The regular frequencies of the PowerColor RADEON X800 Pro are 475/900MHz. The heart of the card is the RADEON X800 Pro GPU from ATI:

Note that the bridge that had been cut with a laser is soldered up in the snapshot. That was a simple operation, but it didn’t help me convert this RADEON X800 Pro into an X800 XT, i.e. turn all the 16 pipelines on. I’ve already met a number of off-the-shelf graphics cards on the RADEON X800 Pro, but none of them allowed turning on all the 16 pipelines by any means. So I have come to this disappointing conclusion: there’s no way to do this modification on off-the-shelf RADEON X800 Pro graphics cards, at least at the moment.

So, we have only overclocking left. Let’s get to it right now!

Increasing the Core Voltage

The GPU power regulator on RADEON X800 Pro graphics cards is based on the FAN5240 chip from Fairchild Semiconductor. The output voltage of the regulator is determined by a digital code, applied to the chip’s VID0-VID4 inputs.

Unlike graphics cards on GPUs from NVIDIA, RADEON X800 Pro cards don’t control the GPU voltage during work: the core voltage is always 1.4v. Curiously, the digital code on the inputs of the controller chip corresponds to an output voltage of 1.0v. This discrepancy arises as the graphics card uses resistances, deviating from the typical connection scheme. For example, the resistance of the R6 resistor (the numeration according to the typical connection scheme) is not 1,000 Ohms, as indicated in the chip’s documentation, but 576 Ohms, as my measurements say.

This resistance should be changed to increase the core voltage. Here, we must increase this resistance, rather then otherwise. So, instead of just soldering up an additional resistor to shunt the R6, I had first to unsolder the R6 resistor and replace it with another. I used a 1,000 Ohms variable resistor as a replacement, soldering it instead of the R6 on wires:

The maximum output voltage of the power regulator is achieved at the maximum resistance of the variable resistor. It is about 1.7v if you use a 1,000 Ohms resistor.