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Old 08-04-2006, 08:44 AM   #1 (permalink)
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Default 7900/7950 GT Voltmod Guide

7900/7950 GT Voltmod Guide

Voltmodding a 7900/7950 GT can be done to increase the overclock you can achieve. If your 7900/7950 GT has a reference PCB, this mod can be done. There are a few 7900/7950 GT’s that don’t use the reference PCB (I think this includes most of the 512MB versions, I could be wrong)

Disclaimer: Nobody on Tech-Forums.net are responsible if you kill your card. Do this at your own risk.

I recommend that you read this guide carefully, and understand what you are doing before going ahead.

the biggest risk is soldering resistors. If you decide to do the resistor mods, be really careful. If you are not comfortable with soldering, I do not recommend you attempt the resistor mods.

The conductive pen mod is not very risky; however I still advise you be careful.
If you only have stock cooling, I recommend a maximum of about 1.4V
Make sure you have drawn the right traces, and they are not touching any other contacts.

What you need to voltmod:
  • Conductive Pen (highly recommended)
  • Soldering Iron (optional, to increase voltage past 1.55V)
  • Solder – preferably very thin (to be used with soldering iron)
  • Resistors (optional)
  • Pencil

The areas in the red boxes are the areas you need to look for when voltmodding your card

Conductive Pen mod:

The above picture shows three possible sets of routes you can use to increase voltage (in the pink boxes)
I recommend using the lower set, because it is the easiest to do. But remember to only use one set.

This is another set you can use. I'd recommend it after the set in the bottom pink box.

Green trace: gives +0.05V increase
Blue trace: gives 0.10V increase
Red trace: gives +0.20V increase

You can combine the colours to make different voltages:
7900 GT
1.2V = none (stock)
1.25V = green
1.3V = blue
1.35V = blue + green
1.4V = red
1.45V = red + green
1.5V = red + blue
1.55V = red + green + blue

7950 GT
1.4V = none (stock)
1.45V = green
1.5V = blue
1.55V = blue + green
1.6V = red
1.65V = red + green
1.7V = red + blue
1.75V = red + green + blue

Resistor Mod:
Note: I recommend you use the same style of resistors used on the card in the first place, like I’ve done. They are kinda hard to find, but worth it.
If you cannot find that style of resistor, you can do what I did and steal resistors from old parts you don’t use anymore (Preferably dead. I have several dead Pentium 3 motherboards which I took the resistors from)

Another side note, that style of resistors is very easy to lose. So be careful.

To increase voltage over 1.55V (1.75V for 7950's - though I don't recommend that), you need 1 x 50Kohm resistor (47Kohm will be fine)

In this picture, the highlighted resistors you see are not the ones that came with my card. I’ve already replaced them, but I don’t feel like swapping them back just for the picture

When you get your card, The red resistor measures 5Kohm. By replacing this with a 50Kohm resistor, you increase the voltage by +0.3V (I used a 47Kohm resistor, which I calculated to give a +0.28V increase)
Replacing this resistor alone increases the voltage from 1.2V to 1.5V (or if you use a 47Kohm resistor, 1.48V)

Do this in conjunction with a conductive pen mod to increase the voltage further.
7900 GT
1.5V = resistor
1.55V = resistor + green
1.6V = resistor + blue
1.65V = resistor + blue + green
1.7V = resistor + red
1.75V = resistor + red + green
1.8V = resistor + red + blue
1.85V = resistor + red + green + blue

7950 GT
1.7V = resistor
1.75V = resistor + green
1.8V = resistor + blue
1.85V = resistor + blue + green
1.9V = resistor + red
1.95V = resistor + red + green
2.0V = resistor + red + blue
2.05V = resistor + red + green + blue

I do not recommend going further than about 1.7V. This is with aftermarket cooling.
so for 7950 GT's, I would recommend choosing either the resistor mod, or the conductive pen mod
these cards can get quite hot if you put the voltage high.

In the picture above, the green resistor controls the switching frequency. It measures 86Kohm
By reducing the resistance to 46Kohm, you will increase the switching frequency, and hence the overclockability of your card.

This can be done by doing one of the following:
  • drawing over it with pencil, and measuring the resistance using a multimeter (if you are not comfortable with soldering, you may want to try this)
  • soldering a 100Kohm resistor in parallel with it
  • replacing the resistor entirely with a 45-47Kohm resistor

Note: this resistor can even be taken down to about 30Kohm if your overclocks are not going as high as you’d like

Heatsinking IC’s:
If voltmodding your video card, it is recommended that you use aftermarket cooling for your GPU. Also some of the IC’s will run hotter with a voltmod.

These 3 IC’s in particular can get hot if you go above about 1.55V

If you go to 1.65V and above, the capacitors at the back of the card can also get hot. You might want to sink them too:

I haven't made a memory voltmod section. at least not yet.
though if anybody else wants to make one and post it here, you're more than welcome to do so

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Old 08-04-2006, 10:12 AM   #2 (permalink)
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Very nice guide!

Also if you didnt add it [I didnt read it thoroughly], I suggest using masking-tape for drawing the conductive ink, so the lines will be nice and smooth.... conductive pen ink flow tends to mess up straight lines no matter how hard you try .

Also, would be awsome if you make another part of the guide showing HOW to solder new resistors not many knows how, me in detial, haha.


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Old 08-06-2006, 04:25 AM   #3 (permalink)
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yes im 16 and havnt had the chance to soder much ( I will practice on a radio or a toy car first , lol) it would help if u did thanks
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Old 08-07-2006, 01:42 AM   #4 (permalink)
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So, how did you figure this out exactly?
E6300 w/ AF7 Pro 3.11ghz
Gigabyte DS3
2GB G.Skill DDR2 800
7900GT w/ Zalman vf900 650/800
Z-5500 Digital Speakers
22" Chimei + 19" BENQ
XClio 3060
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Old 08-07-2006, 07:37 AM   #5 (permalink)
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the knowledge would have originally come from Nvidia employees I'd say. I got the info by reading a lot of stuff, using google.

I'd say xtremesystems and anandtech are worth mentioning, but I did look at a fair few sites.

what I did was collect all the necesary information, and put it all together in this guide.

something I did create was a possible formula for the 50Kohm resistor mod (I'm not sure exactly how accurate it is, because I haven't tested it):
V = kR + C (voltage = V, resistance = R, in Kohm)
1.2 = 5k + c (1)
1.5 = 50k + c (2)

(2) - (1)
0.3 = 45k
k = 0.3/45 = 1/150

1.5 = 50/150 + C
C = 1.5 - 1/3 = 7/6

V = R/150 + 7/6
150(V - 7/6) = R
where V is the desired voltage, and R is the resistance in Kohms required to get this voltage.

again, I'm not sure how accurate it is, so I didn't include it in the actual guide. but that's what I used to calculate that I got 1.48V using the 47Kohm resistor.

one other thing, I haven't seen anyone else sink their capacitors. that was my idea.
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Old 08-07-2006, 07:40 AM   #6 (permalink)
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as long as its your card in the pictures, and you're the one shooting the pictures, you legaly don't own anyone any sort of credit.

what about the rest of the stuff I asked about? ^_^;

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Old 08-07-2006, 07:49 AM   #7 (permalink)
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I might make a soldering guide if I have time, but it's something I don't always have right now, this being my final year of school and all.
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Old 08-07-2006, 07:53 AM   #8 (permalink)
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same here lol..

Well thanks anyway this guide is pretty nice as it is .

I wonder if X1900XT's has any physicall mods..

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Old 08-07-2006, 08:03 AM   #9 (permalink)
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not that I know of.
the ability to voltmod was part of the reason I got my 7900 GT though. that, and it cost a fair bit less than a GTX or any X1900.
I've made it faster than a GTX anyway.
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Old 08-11-2006, 12:32 PM   #10 (permalink)
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