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  How to Volt-mod your GeForce 4 videocard

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How to Volt-mod your GF4 - Part #1

Not too thrilled with this overclock I bought some Thermaltake copper plated aluminum RAM sinks from 1CoolPC, after I had cut them to the right dimensions with a hacksaw and attached them with Arctic Silver Thermal Adhesive I could take the memory up to 607,5mhz without artefacts…

This is when I reached the card’s limits without voltmodding, which I will now describe in detail how it’s done.

Just because I’m using a Gainward for overclocking it doesn’t mean that you should sell your Ti4200 and get the same brand, however it will need to have a Semtech SC1102 Synchronous Voltage Mode Controller IC otherwise this article will not apply 100% for you (I will however explain for you how to do this mod even if you don’t have a SC1102 IC).

Pictured below is my card with the cables attached, the yellow wire will control memory voltage (v-mem) and the red wire will control GPU voltage (v-gpu)

 

Counting from the dot on the SC1102 IC counter clockwise 11pins we come to the pin “sense” (for in-depth details take a look at the SC1102 PDF.)

This is how it works; when you start your computer the GPU is given 1,65volts of current, the GPU then continuously sends back this 1,65v signal to “sense” on the SC1102 IC so it knows that it’s giving out the correct amount of power, should the signal fluctuate the SC1102 IC tries to compensate for this…

What we will do is connect a wire from “sense” on SC1102 to ground, this will make the signal weaken and thus more voltage will be given to the GPU. (Since the SC1102 doesn’t believe the GPU is getting enough current.)

Though we don’t want to send the whole signal to ground because then an infinite amount of power will be sent to the GPU and it will be fried within a second, therefore we will attach a variable resistance on the wire called a potentiometer (pot), this will allow us to adjust the voltage sent to the GPU “on the fly”.

 

I’m using a high-quality pot that I bought from www.elfa.se its product number is 64-745-63, and it costs $2.5. This is a 5k ohm pot that has 20 turns until you reach zero, making fine adjustments very easy. A one turn pot will do but you will have to be much more careful, if you apply too much voltage you could fry the core.

Now we need somewhere to measure how much voltage we are giving the card, a multimeter will be required for this, set it to measure volts : : 20 and then connect it to the underside of the capacitor that is located below the SC1102 IC and first memory, the pictures below might also help:

But what if I don’t have the SC1102 IC you say? Well then the following formula will help you to find out what kind of pot and startup resistance you should use:

First thing you will need to know how much base resistance, or 1/R1 your card has, thus you will need to find the “sense” leg on your IC, a search on google with it’s product number almost always will give you a hit.

Note: these measurements must be made when the computer is off and the card removed from the PC, the volt mod must also not be attached.

For our SC1102 the base resistance for v-gpu was 104ohm from the sense leg 11 to ground, 124ohm was the resistance for v-mem…

1/R = 1/R1 + 1/R2

And since we want to start with a small increase in voltage we multiply the resistance by 20 (104/20=5.2% and 124/20=6.2% increases in percentage gained if starting with a x 20 resistance)

Thus since we had a base voltage of 1.65 and 3.47v, our start-up voltage will be 1.74 and 3.69 volts, respectively.

What this means is that if you don't have the same card as mine and your capacitors are not located at the same place you can measure them all before and after the mod and thus find which one is the right one to measure from.

The resistance of the pot will thus be 1/R2*20, or 104*20 and 124*20, which is 2080ohm and 2480ohm respectively, so a 3k ohm pot would be enough but they are very hard to find thus we choose a 5k ohm.

 



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