How to Volt-mod your ATI Radeon videocard


Volt Modding (continued)

Now we have come to the first interesting mod, the “VGPU” mod, this mod will make it possible to increase your GPU/VPU/Processor voltage. The first thing you will want to do however is to see what your current VGPU voltage is

Use a multimeter to measure the voltage; you won’t be able to do this mod without one. Set it to measure volts in the 2v range and put the positive end on the point above shown (yellow circle) and the ground cable to a ground point in your case (the case itself will do). The red cable and the yellow circle on the left side control VGPU voltage, the blue cable and yellow circle on the right side control VDDR voltage. The black cable is ground.

My card had a default of 1,70 volts, however we will also need to know the base resistance of the card before doing anything. To measure this you will need to remove the card from the computer (after grounding yourself with an antistatic wrist strap) so it does not interfere with the resistance. If you do not know what I refer with “grounding”, please stop working on this mod now and read this before continuing, “About ESD Control”.

Set your multimeter to measure ohms in the 200ohm range and measure the resistance from the sense leg, on VGPU this is either leg 18 on the “Semtech 1175” IC or solder pad C88 where my red cable is attached. Leg 20 is ground. For VDDR it is leg 5 on the “Intersil 6522” IC or the solder pad that the blue cable is attached too. The leftmost pin with number 7 is ground.

For both, measure these to ground (the face plate on the card), record these values on a piece of paper along with the voltage and go find a calculator and bring back the memories of school mathematics. If you can’t make sense of this don’t just skip this part because if you calculate this wrong you will end up with a very expensive doorstop.

My base voltage was: 1,70v
My base resistance was: 220ohm

This is the formula: Vgpumodded = VGPU * [1+ (base resistance/VR resistance)]

A good resistance value to start calculating from is around 10k ohm:

1.7 X [1+ (220/10000)] = 1.73V

Thus when you do the mod, the new minimum voltage i.e. when the pot is set to its maximum resistance of 10k ohm will be 1,73v with a 10k ohm pot. This is safe, only a 0,03v increase.

The voltage modification for the memory “VDDR” is very similar, the only difference being that it has another base resistance and base voltage, a good starting point for a resistor will be around 20k ohm. When you have come this far you are probably wondering what to do next, you have understood the formula and have calculated what sort of resistance will be good for your card.

This brings us to the Voltage Controllers on the graphics card, my card uses a “Semtech 1175” IC for controlling the voltage sent to the GPU, if you download its PDF file you will see that pin 18 comes labelled as –IN1 “Inputs of close loop error amplifiers. Works as a feedback input” That describes it pretty well, this pin is responsible for receiving a power signal from the processor, in our case it’s a 1,70v signal. This tells the Semtech 1175 controller that it is providing the correct amount of output voltage based on a reference resistance. What we will do is leak a small amount of this 1,70v signal to ground, thus the “Semtech 1175” IC will be fooled to thinking that it is not supplying the GPU with enough voltage and thus it will try to make up for this lost voltage.

The same applies for the Intersil 6522 IC that controls VDDR, only here pin 5 is sense and pin 7 is ground. You will locate these PDF files using Google, both of these Integrated Circuits (IC) will come up on top when you do a search for their part numbers on Google (SC1175 and ISL6522).


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