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5850 Voltmod Thread

post #1 of 89
Thread Starter 
I have removed the original post here, and replaced it with the vCore mod for the 5850.

This has not yet been wired up, but the schematic has been confirmed by several experienced modders. It looks basically the same as the 5870 mod using a 50 Ohm trimmer from FB to ground.

This mod is performed on the face of the card, between the PCI-E plugs and the fan header.

I TAKE NO RESPONSIBILITY FOR THE DAMAGE CAUSED BY THIS MODIFICATION. USE THESE INSTRUCTIONS AT YOUR OWN RISK. THIS WILL VOID ANY WARRANTY IN PLACE ON YOUR 5850.

Huge thanks to CL3P20!


Edited by theta - 1/28/10 at 10:36pm
post #2 of 89
Thread Starter 
This should also help, since there is no data sheet:

post #3 of 89
Thread Starter 
Lastly, some macro shots that I've taken of my cards:


post #4 of 89
the first thing you are going to need is a DMM to measure the resistance between the FB and ground

EDIT: looking for data sheet, this is a hard one to find
Edited by Voltage_Drop - 1/20/10 at 6:47pm
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post #5 of 89
Thread Starter 
FB to ground w/ power off is 3.0-3.1 ohms.
post #6 of 89
Quote:
Originally Posted by theta View Post
FB to ground w/ power off is 3.0-3.1 ohms.
Now is that 3.0k-3.1k or is it in just Ohms? That resistance seems kinda low that is why I am asking. Also MADMAX22 has been experimenting with this same chip but it was on the 260 and I believe he has also found the OCP mod for it to keep the voltage from dropping at to high of a load. I would also recommend that you get an aftermarket cooler for your card if you havent already done so because with a Vmod you are going to see an increase in temps with the stock cooler and could possibly damage the card if you dont keep the temps in check.
Edited by Voltage_Drop - 1/28/10 at 11:55am
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post #7 of 89
Check the resistance on the resister I have marked with blue.

Or the resistance of the pin I have marked.

That is the pin and corresponding resister I modded on my gtx260 with the same chip for the OCP mod.


Another thing, its kind of a crazy process but it works, I can bench my 260 at 837core 1674shader.

Open up the bios for the gpu with nibiter and change the highest voltage to what ever you want to run. Atleat thats how I did it. I have the bios changed to 1.4vgpu and then lower it to around 1.34v with software since thats about the extent of getting good results on water. I could go higher one xtreme cooling but dont have it.

Then with rivatuner I force it to 3d mode so that it doesnt downclock on me.

Ill post some guides later if you want.

Edited by MADMAX22 - 1/28/10 at 12:58pm
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post #8 of 89
Thread Starter 
Quote:
Originally Posted by Voltage_Drop View Post
Now is that 3.0k-3.1k or is it in just Ohms? That resistance seems kinda low that is why I am asking. Also MADMAX22 has been experimenting with this same chip but it was on the 260 and I believe he has also found the OCP mod for it to keep the voltage from dropping at to high of a load. I would also recommend that you get an aftermarket cooler for your card if you havent already done so because with a Vmod you are going to see an increase in temps with the stock cooler and could possibly damage the card if you dont keep the temps in check.
It's strangely enough 3.0-3.1 ohms. I may be new here, but look on X-S, etc.

Now, that is in an off power state, have not tested while power is applied, since I'd need to solder to the leg for a good reading.

Quote:
Originally Posted by MADMAX22 View Post
heck the resistance on the resister I have marked with blue.

Or the resistance of the pin I have marked.

That is the pin and corresponding resister I modded on my gtx260 with the same chip for the OCP mod.


Another thing, its kind of a crazy process but it works, I can bench my 260 at 837core 1674shader.

Open up the bios for the gpu with nibiter and change the highest voltage to what ever you want to run. Atleat thats how I did it. I have the bios changed to 1.4vgpu and then lower it to around 1.34v with software since thats about the extent of getting good results on water. I could go higher one xtreme cooling but dont have it.

Then with rivatuner I force it to 3d mode so that it doesnt downclock on me.

Ill post some guides later if you want.
I will check those points now. These BIOSes can not be edited for voltage yet in RBE.
post #9 of 89
Thread Starter 
Got it - 4.33 kOhms (4330 Ohms) on that resistor / leg to ground.

And to reiterate, 3.0-3.1ohms from FB to ground. I know it's low.
post #10 of 89
Quote:
Originally Posted by theta View Post
It's strangely enough 3.0-3.1 ohms. I may be new here, but look on X-S, etc.

Now, that is in an off power state, have not tested while power is applied, since I'd need to solder to the leg for a good reading.


I will check those points now. These BIOSes can not be edited for voltage yet in RBE.
If that is what it reads then that is what it reads. MADMAXX was able to adjust the BIOS voltages because he has that chip on an Nvidia card as oppossed to your ATI card which is not supported as of yet for voltage changes. Post the link of the XS site where they did the mod so when can have something to go off of. Thanks
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