8800 gs pencil mod

First off…Disclaimer: I wouldn’t recommend trying anything of this. If you do and you damage your card, I am in no way responsible.

Ok….now that that’s over with…

I recently built a budget gaming rig and went with the XFX 8800gs (hard to beat $100 AR).

My first attempt at overclocking I maxed out at 740/1674/950 (at 1728 shaders, I was unstable over 680 core). I tried bumping up the core voltage with a bios flash, but it didn’t make my card any more stable. The one thing I did find was that after the bios flash, I was able to overclock the memory to 1020 (probably because I used memory timingset #0).

After doing some searching for a physical voltage mod, I found this picture.



This is the PCB for the XFX 8800GT, but the layout is exactly the same as my 8800gs. I couldn’t find a data sheet for that chip (BN-9G), so I just took it for what it was and hoped the picture was right.

First thing I did, was measure the resistance of the resistor (circled in green). Turned out to be 135.7 Ohms. With a 5K resistor in parallel…the final resistance would be about 132 .1 Ohms. Rather than get out the soldering iron, I got out a pencil and decided to see if I could lower the resistance that way. After lightly shading it, the resistance dropped to 134.1 Ohms.

Now, the only problem I have is that I don’t know where I can put a probe to measure the core voltage. Despite this, I still plugged the card in and booted it up. Opened up speedfan and my VGA temps were only at 35C. I started overclocking and was able to get my card stable at 770/1728/1020. I bumped the core up to 775, but my screen locked up and the motherboard started beeping. Im guessing this was caused by an OCP circuit because everything was fine after I rebooted.

After some more testing, I settled on 756/1728/1020. I got it up to 720/1782/1020, but I artifact in atitool after about 3 minutes. At these settings, my temps never went over 55C in speedfan. I’m using a Zalman VF900-Cu cooler with 2 PCI exhaust fans (stock cooler was way too loud, plus I had a gift card to use). After running 3DMark06 my scores went up about 300pts (upper 11500’s to 11866). I’m guessing that my CPU is starting to bottleneck the GPU (e2180 at 3.45GHz).

I’m going to play with this some more this weekend. I’m going to try to pencil some more to lower the resistance down to about 133Ohms. Plus, I’d like to be able to monitor the GPU core voltage, so if any one has any ideas on how to do that….please let me know.

How do you calculate the vGPU change? Even if I did the hard mode, the drop in resistance would only be about 4 ohms. Unless they meant to use a 5k trimmer...but then id still need to figure out where to put a probe to monitor the vGPU.

largon...thanks for the help.

I'm assuming these are the mosfets your talking about? (circled in red)


or the ones that are on the other side of the card?

Also, excuse my ignorance, but which pin do I want to check the voltage on. I'm mostly a software guy, so I know theres usually a gate, drain, and source pin...but i know little beyond that.

Again...thanks for all the help.


Also, as a side note, I penciled that resistor down to 131.9 ohms and I now have my card stable at 756/1782/1020. I think thats about as far as I can go with the pencil...so I may have to try the hard mod later. Still... from 740/1674 to 756/1782 isnt too bad for about 10 seconds of pencil shading.

Sweet...i finally broke 12000 in 3dmark06. I was able to pencil the resistor down to 123.5 ohms. This gave me a gpu voltage of 1.29v idle and 1.32v load. I got my clocks up to 770/1890/1020. I think the core clock could go higher, but I either freeze or get a black screen when I put it higher that 775 (OCP?).

The lowest variable resistor I have is 10k...so i'm going to try and see how much farther I can go with the pencil.