How to: Vmod your 8800 GS/GT/GTS /9600 GS/GSO/GT - - An Overclocking Community
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How to: Vmod your 8800 GS/GT/GTS /9600 GS/GSO/GT

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post #1 of 632 (permalink) Old 09-28-2008, 02:11 PM - Thread Starter
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I have been getting a lot of inquiries lately on how to volt mod the 8800GS and 9600GSO for GPUv.. these being such stellar deals for folding farm additions and monster OC'ers both make them great choices for a cheap GPU.

The 9600GSO is the same re-branded GPU as the 8800GS..both feature similar if not the same PCB types, and Primarion control IC. Both have the same number of SP's and run 192bit memory buss'.

For starters, I thought that I would mention the easier alternative to the "hard-mod", which would be a BIOS flash. Just flash a standard GS or GSO with the BIOS from a GS/SC edition, and you will be able to enjoy 650mhz startup core speeds as well as increased shader clock of 1620mhz. This ^^^ is not were we are going today though!!


For starters.. the Vmod candidate. A standard PCB rev, GS/GSO/GT/GTS all have this similar layout..and this mod works for all of them.

Above is the standard rev. PCB for: ..EVGA and a few others


Above is the non-standard PCB for: ..Palit, XFX

Attachment 86853
Attachment 86854

Above is the standard PCB for: ..XFX

Zotac 9600GT

EVGA Dual-slot 9600GSO

GPUv: 100k ohm VR -> ground
*stock resistance value ~3.92k ohms

tuning VR for ~72k ohms will get you close to 1.1v..


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post #2 of 632 (permalink) Old 09-28-2008, 02:12 PM
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Things you will need:

1. 500 Ohm Variable Resistor [for EVGA], or 5k Ohm for XFX and 20k for Palit
2. DMM [Digital MultiMeter] both for voltage measurement and tuning the VR's before installation.
3. 15-25W solder gun
4. Solder [of course ] the smaller diameter and least amount of lead FTW.
5. Electrical tape
6. Super Glue
7. An extra IDE cable
8. Small flat-tip screw driver for adjusting the VR


9. Coffee [what? Its morning here!]
10. Steady hand. [If you dont have one, substitute yours for someone else's]

Let's see...

Ok, we got everything together, now for some fun!
For my victim, I choose to start with a 8800GS/SC [after rebates, it was ~45$ ] It is generally a good idea to clean the mod area, with a Q-tip and some alcohol before starting. If you need pics of should stop here!


First, you will want to tape off the mod area, as carefully as you can, using the electrical tape. Cut short 1-2" pieces and place them around the resistor to prevent damaging other components on the PCB. Making sure to leave a small opening in the center, for us to solder our VR in-line.


Now that that is done, lets have a look at the VR's. Remove one of the outer legs on the VR [either one is fine], leaving only one outer leg and the center leg, still attached. Using your DMM, set to Ohms, and clip the ground lead to your VR, the posistive lead to the outer leg on the VR. We are now reading resistance through the VR..and need to set it for its max value of ~500 Ohms. You must do this step NOW, before connecting the VR to the you will not be able to read the resistance level, once the VR is soldered into the circuit. Since the resistance level directly corresponds to the new voltage risk blowing your GPU if you do not tune the VR before soldering it in-line.

VR, *out of box*- Attachment 83880
VR, ready for installation- Attachment 83881
Measuring resistance on the VR-

*** A very important detail-> Make sure you have identified which way increases resistance for your VR. This is a crucial part..mark your VR, with a pen to indicate which direction you should turn to raise Resistance [which will lower GPUv]
Before we start up the 'guns'..I thought I would mention a useful tidbit..


I like to start with an old IDE ribbon cable. By cutting a few of the wires, at the back of the connectors, you can strip off a few together.

IDE cable..cut-
Stripped pair for modding-

* These small wires are ideal for IC connections [as these mods usually are] also useful for mobo mods as well. They are easy to strip w/ a good thumb nail, easy to cut and bend..and take solder at a very low temp.
..Lets move on.

Solder !

I prefer to solder my wires up to the VR first, as the connections to the IC chip are very fragile and can break off easily if moved too much. After you have soldered your connections to the VR, use some of the super glue to mount the VR an exposed edge of the GPU's PCB.

Connections to VR complete-Attachment 83879
VR mounted-Attachment 83878

Now to solder the connection from the middle leg of the VR [Ground] to one of the many ground positions on the PCB. I chose a ground point close to the GPUv measure point.

Soldered Ground connection-

Making the next connection takes patience and some skill...practice before hand, you will want to get this right within the first 2 attempts, are it is likely, you will burn the 'pad' and not be able to mod after that. Since we are not landing directly to an IC or a resistor, there is little risk in damaging the card from burning this solder pad...there is a risk you can burn or solder a surrounding tape off the area WELL before proceeding.

Finished result, after removing tape-

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post #3 of 632 (permalink) Old 09-28-2008, 02:12 PM
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Double-Check -

With you DMM, set to continuity [*beeps* when you touch the [+] to the [-] ] Check for the *beep, by measuring across both legs of the VR..if you have tone, your VR is hooked up and in-line... if not, you need to re-solder one of your connections. After you have verified the connections are good, you 'seal' them up with a small dot of superglue, to make sure they dont break off, moving the GPU around.

Assuming all is well..Lets move on...

1. Secure any loose wires with some more super-glue, or a piece of electrical tape. Then re-insert your GPU, back into the mobo..DO NOT TURN ON YET!!!

2. Set your DMM to Volts DC and get ready to measure GPUv as we start up.
*Find bare metal in your case, for the [-] lead, and place [+] lead on one of the GPUv measure points in the first photo.

3. Fire up the rig, as you monitor GPUv..if you see volts in excess of ~1.28-1.3v..shut down and increase the resistance on your VR. *Using the 500 Ohm VR set at ~max, you should have a slight increase in GPUv over stock..this will prevent not having enough voltage to start the GPU upon Boot-up.

4. With a stock GPUv of ~1.08v under load, I decided to start with 1.18v ..and see how the GPU responded to core increases and to monitor temps.

Measuring stock voltage-

Tuning GPUv after completed mod-Attachment 86855

Testing and Verification-

After monitoring my temps and a few back-to-back 3D runs of 06' and 05'..I ended up with the following results:

Stock 8800GS/SC: 650mhz core / 1620mhz shader / 950mhz vmem
1.08v under load, ~1.06v idle

Vmod'd 8800GS/SC: 804mhz core / 1944mhz shader strap / 950mhz vmem
1.25v under load, ~1.21v idle

3D Mark 06' score- 14,487 points
FutureMark verification- on Air

1st Place 3D '06: 16,503 points @ 1028mhz core/ 2217mhz shaders/ 1028mhz memory- Slushbox WC'ing @ -52c

2nd Place: 3D Mark 06' SLI Record-18,649 points

2nd Place: 3D Mark 05' SLI Record-23,557 points

2nd Place: 3D Mark 03' SLI Record-61,723 points

Hardware Hall of Fame 3x 2nd place hardware rank for 8800GS 320mb SLI, 3D Mark and 1st place for single GPU in 3D Mark '06


For my OC I use RivaTuner..I feel it is the best GPU related OC program ever also features monitoring functions, which accurately detect core/shader and mem speed changes, as well as strap resets [which cannot be visibly seen by any other program [exception for Precision Tuner]!!]
**Keep in mind, all this was accomplished with stock cooling!!

Increasing GPUv to ~1.28v idle/ 1.31v load, I was able to bench again at 828mhz core/ 1998mhz shader strap/ 977mhz mem...bumping the shaders up to the next strap setting at 2052mhz, required modding RivaTuner's slider tables, for more speed adjustment in the program..and raising the GPUv to 1.30v idle.. 1.339v load

Good luck to those who will be modding... I have a feeling my record won't be around for too much

Good luck to you, and good modding!!


Updated pics of completed mods/GPU's

EVGA 9800GT: GPUv and voltage measure point installed : for Jarble of OCN

GPUv and vMEM mods completed, with vmeasure

Dual-slot 9600GSO: GPUv and vMEM completed : measuring set GPUv

1x of my EVGA8800GS: GPUv and vMEM + 4x secondary cap's

close-up of vMEM, completed

close-up of 2ndary capacitors on 8800/9800: 2x SMD type and 2x 'cans'


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post #4 of 632 (permalink) Old 09-28-2008, 02:24 PM
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A lot of people will be happy with this guide! Thank you.

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post #5 of 632 (permalink) Old 09-28-2008, 02:30 PM
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update completed.

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post #6 of 632 (permalink) Old 09-28-2008, 02:42 PM
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looks like a trip to radioshack is in order. +rep

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post #7 of 632 (permalink) Old 10-01-2008, 09:31 PM
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where did you get the VR's @

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post #8 of 632 (permalink) Old 10-01-2008, 09:39 PM
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I bought mine at radio shack too! They have a lot of them.. or a Fry's!

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post #9 of 632 (permalink) Old 10-03-2008, 05:03 PM
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Just got back from RadioShack and they had everything I needed but the VR.....Damn... where to get them?

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post #10 of 632 (permalink) Old 10-03-2008, 05:28 PM
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So, I've only a soldered a few times in the past, is this something I can safely undertake. Also, I have the standard xfx version flashed to XXX BIOS. Do you think the PCB will be different then what you have posted here?
Also, have you benchmarked any games running this card at those clocks?

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