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).
