by Oleg Golubovich
10/17/2006 | 08:21 PM
Games and benchmarks, maximum frame rates, display resolutions, full-screen antialiasing and anisotropic filtering are all those things that don’t let inveterate gamers and PC enthusiasts sleep well. There are at least two reasons for the race for a higher numerical expression of the power of the computer at large and of the graphics card in particular: 1) hardware requirements to new games are growing at a very fast rate, 2) getting the maximum out of PC hardware has become something like a new kind of sport.
<%BANNER[article]%>Our today’s review has been written for people who take overclocking seriously and have access to the newest and best computer hardware. Not many of us can afford a GeForce 7950 GX2, let alone to dare to volt-mod this $600-700 product. Yet it is really exciting to experiment with such an extraordinary graphics card.
So, I am going to deal with EVGA’s GeForce 7950 GX2, although the brand doesn’t matter at all. All graphics cards of that family are manufactured by Nvidia and are distributed among other companies who are eager to put their stickers on the cooler and sell the card under their own brands. The volt modification for the GeForce 7950 GX2 can be applied to every such graphics card regardless of the manufacturer who acts as an intermediate in this case.
Before getting to the point of the review, I want to give you a couple of descriptive lines and photographs.
The EVGA e-GeForce 7950 GX2 consists of two PCBs that are united into one graphics card to enable SLI mode and to provide an opportunity to build a Quad SLI subsystem. Here are photos of the top…
…and bottom parts of that sandwich:
I can give you a few interesting photos you can’t see in every review because I have to dismantle the graphics card anyway. To do that, I have to unfasten the four screws on the reverse side of the card. Then I carefully take the whole thing apart. Do not forget that the PCBs are additionally connected with a special adapter, a SLI terminator of a special design:
Now I can remove the coolers to take a closer look at the PCBs. The top PCB comes first. It is powered fully from the power supply’s 12V line.
And this is the bottom PCB:
Take note of the small chip that resembles a HSI bridge:
This chip is responsible for the communication between the PCBs and that they work together as a whole.
Samsung’s 1.4ns chips are installed on GeForce 7950 GX2 cards:
Now we can take a look at the cooling system such graphics cards come with. Here’s the native sticker from Nvidia:
The plastic casing that covers the cooler’s ribs is secured with two screws you can find right under the sticker. Generally speaking, the cooling system they install on the GeForce 7950 GX2 is very bad. Here’s a photo of its back side:
The copper sole and the good thermal interface are all right, but won’t help much when the heat dissipation area is so small. Just count up the number of the ribs:
This is in fact a folded sheet of, hopefully, copper.
So, we’ve got a cooler made of an aluminum alloy, with a copper insert in the base and a few ribs. It cools the GPU and, through thick thermal pads, the memory chips. On the bottom PCB it also cools the chip that combines the two GPUs into a SLI tandem. And this is the cooler of a top-end product! The cooling quality is poor, to put it mildly. Even in idle mode, the driver and RivaTuner RC 20 reported a temperature of 50°C – prior to any modifications. The level of noise in 3D application is a different issue. Two fans are louder than one, you know.
Let’s leave it to Nvidia’s engineers to work on those issues, though. Before attempting to volt-mod one of the most expensive graphics card available today, read the following disclaimer and think again if you indeed want to do that.
The modifications described in this article have been successfully made in practice. Each mod was tested by us and helped achieve the desired result. We don’t accept any claims concerning damage to your graphics card or any other PC component after the modification because such problems imply your own mistakes. The author and X-bit Labs are not responsible for any damage inflicted by repeating anything of what is described in this article. We also cannot promise you that your final result will be as good as ours due to the variation in the potential of particular samples of graphics cards.
Warning! Volt-modding, if recognized, makes all warranty obligations void.
You should take up volt-modding if all the following items are true:
Before doing any volt-modding, make sure the graphics card is properly cooled (sometimes the standard cooler may be insufficient even for ordinary overclocking).
To modify a GeForce 7950 GX2, you need:
Before doing the volt-mod, I want you to be aware of the pitfalls you may encounter while modifying the graphics card.
The volt-mod is the same for both PCBs despite the certain differences in their design.
First, I will tell you how to modify the core power circuit. This circuit is based around an ISL6568 regulator from Intersil in a rather awkward packaging. It’s good we don’t have to solder anything to its pins.
I will change this voltage discretely with a step of 0.05V. What’s curious about the modifications you can apply to your GeForce 7950 GX2, in most cases you can do them with a simple lead pencil (but remember that the lead from the pencil isn’t long-lasting, is unreliable and may crumble away from the card) or any current-conductive lacquer or glue. A rear window defroster repair kit is recommended by users, too.
There are two ways to volt-mod the core. The first way is rather simple and easy. The second calls for more solid skills in soldering rather than in drawing with a pencil but allows to reach a higher voltage.
The voltages must be monitored somehow. So, find out the following point on your graphics card first:
By default, the core voltage is 1.3V.
To increase it to 1.5V, you have to close the two contacts near the voltage regulator:
Next you can increase the voltage to 1.55V by closing the other pair of contacts. Do not forget that you have to close the first pair before closing the second one. And never turn a PCB on independently! First, make the mod on both PCBs, then put the graphics card together again, and then test the modification in practice.
There is another volt-mod method to increase the voltage to a higher level. In this case, you should remove the 1.5-1.55V modifications. To perform it, you should unsolder the resistor marked in the picture and replace it with a 50,000Ohm resistor.
The original resistance is lower than necessary, and there is no other way to change the resistor ratio that determines the resulting voltage on the graphics chip. You can take a variable resistor instead of a constant one and set it at the necessary resistance as I did. I set 47-50,000Ohms before soldering the resistor in. This increased the core voltage to 1.61V.
To increase the voltage further to 1.65V, you need to close the contacts shown in the picture (the resistor you’ve soldered in to get 1.61V must remain in its place).
I didn’t test the graphics card to find the highest stable core frequency due to its very high temperature with the native cooler. I only made sure the described modifications really worked.
First, I want to show you the points where you can monitor this voltage:
These points are convenient for the bottom PCB, but what to do with the top one? You should go right to the regulators: the voltage is monitored on the outputs of the filtering coils:
By default, the GDDR3 memory works at 1.9V on this graphics card.
To increase the voltage, you should solder a 10,000Ohm variable resistor in parallel to the resistor marked in the picture and reduce its resistance.
The resistor can be replaced with a pencil mod: the reduction of the resistance from the original 585Ohms to 525Ohms helped increase the voltage to 2.05V. Before the modification, the memory on my sample of the graphics card was stable at 830MHz at best. After the voltage increase, it worked at 880MHz. I think this is not the limit because the chips were under very harsh thermal conditions.
The graphics card wasn’t benchmarked before or after the modification due to the reasons explained above.
Despite the relative simplicity of the described volt-modifications as they are, there are a number of unpleasant surprises awaiting those who dare to volt-mod the GeForce 7950 GX2. It is going to be a daunting task even for an experienced volt-modder.
Particularly, it is difficult to improve the card’s native cooling system (but it must be replaced because the card finds itself under very harsh thermal conditions even at the default frequencies). Do not forget that you have to modify both the PCBs in the same way so that one of them didn’t become a bottleneck.
And finally, you need to have a good processor capable of keeping pace with an overclocked GeForce 7950 GX2.