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Nvidia 7950 GX2 reference PCB


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Nvidia 7950 GX2 reference PCB








Vgpu Volt-Mod


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).






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.

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