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Old 04-04-2008, 01:29 PM   #1
Clock Killer
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Join Date: Dec 2007
Location: Ga
Posts: 679
XFX 8600gt vmods

Well I have the UDF3 version of XFX's 8600gt. It has 256mb DDR3 ram and it overclocks quite well out of the box from 540/700 to 700/900 (core/mem)

In my never ending quest for more performance I have found a vmod guide for this card, yet it is somewhat inaccurate. Here is the guide I found for this card. It is actually not an 8600gt in the picture but an XFX 7600gt vmod. They do infact have the exact same PCB. There are only a few different transistors and such but the vmod for both cards are the same.

In the 8600gt picture, the ohm readings are way off. I will post the actuals later but both are about 100ohms more. The Vmem and Vgpu reading probes in the 7600gt picture are actually compatible with the 8600gt too, IDK y they blacked them out. Instead of it being a hole that you probe, it is a capacitor leg.

Just thought I'd share my findings with the community.

Additional Comment:

Well after the pencil mods and my voltages at 1.45v core and 1.95v RAM I got my clocks right up to 775/975 (core/mem)

They got there very easily. I'm sure they can go higher and now this card plays crysis on medium settings at 60fps. Im happy with that.

Additional Comment:

I'm still looking for the stock vgpu on this card.

You guys can use the info below to find out what your stock Vmem should be.

If the serial number on the RAM chips starts with "H", NOT HY:
Look at the 5th character:

V: VDD =3.3V & VDDQ = 3.3V
A: VDD =3.3V & VDDQ = 2.5V
Y: VDD =3.0V & VDDQ = 3.0V
U: VDD =2.5V & VDDQ = 2.5V
W: VDD =2.5V & VDDQ = 1.8V
S: VDD =1.8V & VDDQ = 1.8V
Q: VDD =1.5V & VDDQ = 1.5V
R: VDD =1.2V & VDDQ = 1.2V

If the serial number on the RAM chips starts with HY:

V: VDD=3.3V & VDDQ=2.5V
U: VDD=2.5V & VDDQ=2.5V
W: VDD=2.5V & VDDQ=1.8V
S: VDD=1.8V & VDDQ=1.8V
C: VDD=1.5V & VDDQ=1.5V

Additional Comment:

With 610ohms on vmem that yeilds about 1.95v
With 585ohms on vgpu that yeilds about 1.46v

Watch your voltages carefully though. I have two of these cards in SLI and my secondary card seems to need less resistance to gain that same voltages, which leads me to believe that not all cards are the same.

Additional Comment:

Heres the locations of the pins that you need for a variable resistor mod. Solder those pins to a leg of a VRm then the middle pin of the VR to ground.

Additional Comment:

Let it be known that the Mem voltages are VERY finicky. I killed two cards because of it. I would only step up the voltage to 1.9 if I were you. The gpu voltage has alot more leaway.

Last edited by D-Rock; 04-04-2008 at 01:29 PM. Reason: Automerged Doublepost
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