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MSI NX6600GT TD128E vCore Mod

post #1 of 22
Thread Starter 
I finally found a pic of the volt mod that I did to my MSI 6600GT card.

Replacing the standard cooling system with something more efficient, for example with a water-cooling solution, and pulling up the voltages are the traditional means of increasing the overclockability of a graphics card.

The graphics card under question has GDDR3 memory chips from Samsung, known for their low overclockability which doesn’t grow much even after a voltage increase. So I didn’t tamper with the memory voltage on the reference card at all – it wasn’t worth the trouble.

The overclockability of the graphics processor is another matter, as we deal with NVIDIA’s first GPU made with the 0.11-micron tech process. The thinner tech process and the smaller transistor count in comparison to the GeForce 6800 series should render this chip capable of working at higher clock rates.

Let’s check it out. The core voltage regulator is based on the ISL6534 chip from Intersil. It is a dual-channel pulse-width controller capable of driving a line regulator. One of the channels supplies power to the GPU. Unlike the regulators on GeForce FX 5950 Ultra or FX 5900 Ultra cards, which have digital inputs for setting the output voltage level and capable of adjusting the output voltage “on the flyâ€, this chip uses a resistor devisor for setting the output voltage.

Curiously enough, the NVIDIA engineers made this regulator change the output voltage “on the flyâ€, too. Receiving the control signals from the GPU’s registers, two transistors attach resistors with preset resistances to the devisor, thus adjusting the voltage value. Voltage regulators on NVIDIA GeForce 5900 XT cards employ the same idea, by the way.

In order to lift the voltage of the graphics processor, you only must reduce the resistance of one of the divisor’s resistors. That’s exactly what I did:



You can see the controller chip of the voltage regulator in the top left corner of the snapshot, while the output voltage control scheme and the two resistors of the devisor are in the center. The arrows point to the spots I soldered an additional variable resistor to. If you want to test the vmod before you make it permanent, just scribble a little #2 pencil lead (graphite) over the resistor. This will lower the resistance and basically do the same thing that the potentiometer is dong. However, it's not nearly as easy to controll the voltage that way.

This pic shows where you check the core voltage:



In doing this, I was able to increase my core speed up to 680 Mhz!

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post #2 of 22
Where do the wires go that soldered to the resistors? Also, if I wanted to do this to my card how do I find out which resistor I need to use?
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post #3 of 22
Thread Starter 
The other ends of the wires go to a 10k ohm potentiometer. I suggest you do the "scribble" method first, to see how much further your core can go with more voltage before you spend the time making it permanent by soldering. Scribble graphite from a #2 pencil over that resistor to test your core. More graphite (a harder scribble) the less resistance, and therefore the higher the voltage will go. I think the max is 1.8 volts, or at least that's as high as I could go on my card.
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post #4 of 22
What cooling do you have on the card?
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post #5 of 22
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Actually, I was running a modified PIII heatsink, but when I pulled it off to put my water block on, I snapped a resistor off so I no longer have the card. At first I was running the Zalman 700 and it cooled it well enough. With the heat these cores can take, the Zalman will get you pretty far. I traded my Zalman for the waterblock, and when I was waiting for my block in the mail I was running the PIII heatsink. When I finally got the waterblock in I got in a hurry, and now my card is a really expensive paperweight...

BUT I was running air when I did the benchmarks (nVidia benchmark section) so you can see what a little voltage can do.
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post #6 of 22
I just volt modded my 6600GT on both the gpu and memory, and the volt mod that I did is quite a bit different than yours. I will post up pics and a guide in the next couple days.
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post #7 of 22
pretty mcuh every manufacturer has a different PCB layout than all the others, thats what makes it a bit hard whe ntrying todo it on another 6600 / gt
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post #8 of 22
Humm there is hope for my 6600GT! (err. calling lando)
    
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post #9 of 22
Quote:
Originally Posted by Lucid
pretty mcuh every manufacturer has a different PCB layout than all the others, thats what makes it a bit hard whe ntrying todo it on another 6600 / gt
Actually, most PCI-E 6600GT's follow the reference pcb desing, so they are the same. I looked at about 4 different 6600GT's, and they were all exactly the same. The agp 6600GT is a different story, however.
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post #10 of 22
Quote:
Originally Posted by wowza
Humm there is hope for my 6600GT! (err. calling lando)
yantronic, Shamino & viperjohn know their stuff too, though VJ has never worked with a 6600, let alone see one hah.
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