8800GT voltage mods

I set the OVP resistance stepwise down to 2,7k.
At 3,6k the GPU core droped down from 1,3V to 1,05V idle without changing the GPU core resistance .
After setting 1,3V GPU core like before, it still shuts off.
I turned the OVP resistance down to 2,7k and the core voltage droped down to 0,95V.
Set it again to 1,3V and got still a shut off.


I think we are wrong with this resistor for the OVP mod.
We need that ..... datasheet.

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Originally Posted by Mysterfix

I had my card black screen on me last night after about an hour of Crysis.:shakes:

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i could play through the crysis demo without problems @ 864/2106/950 but once i started playing stalker i would get black screens (driver crash?)

i went down from 1.35v to 1.27v and lowered the clocks but no matter what i was still getting the black screens, (i haven't done OVP mod)

is it possible that the cards just can't handle the voltage? or do we need a better OVP mod?

Set it to max. 1,22V idle. That will give you ~1,27V load.
Then you have a little reserve to shut off voltage.

While a aquamark run the Voltage jumps aprox 0,05V around.

i set my voltages while running 3dmark06 1680x1050, so the 1.35 and 1.27 was @ load

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Originally Posted by winbond

i could play through the crysis demo without problems @ 864/2106/950 but once i started playing stalker i would get black screens (driver crash?)

i went down from 1.35v to 1.27v and lowered the clocks but no matter what i was still getting the black screens, (i haven't done OVP mod)

is it possible that the cards just can't handle the voltage? or do we need a better OVP mod?

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I measured the vgpu during black screens and got a reading of 0.01v vgpu which should indicate that the card shut down due to OVP. I also don't get that problem when the card is running 1.3v or below.

Is there anyone here who've done the vmod and still are on air?
I'm using a VF900-Cu and my load temps are aprox ~60c.

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Originally Posted by largon

Yes.
"2000MHz" is actually just 1000MHz but since we're talking about dual data rate memory it's effectively 2000MHz (= DDR-2000) - which according to a "certain BFG technician" is bad for Qimonda GDDR3.

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Hmmm ok think im gonna lower my RAM just in case then and OC the core some more. I only got heatsinks on the RAM but watercooling on the core so it should be able to get to some nice speeds.

So even with the OVP mod, voltages over 1.3V seem to be giving problems?
I am going to do the vCore mod tonight and see what speeds can I get without going over 1.3V.

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Originally Posted by Viktor

Is there anyone here who've done the vmod and still are on air?
I'm using a VF900-Cu and my load temps are aprox ~60c.

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Yes I am. I ran it at 1.285 @ 810/1944/2000 stable in Crysis for hours. But my load temp was 50C before bios/voltage mod on a Thermalright V2. You may have to stop at 1.25 or so. Those are load voltages. I upped it to 1.335 and got 830/2000/2000 stable in ATItool and temp was 60C. I really don't want to hit the OVP though so I didn't go any higher.

OK, so for the soldering end of things, what do most of you use? The 7900GT volt mod required a conductive ink pen, that was easy. I have a micro tip iron and the low temp solder. What do you guys use for a magnifier?

If you all are putting in a 1k resistor, then how are you all doing to further adjusts the voltages? What voltage the the VGPU is the 1k Resistor resulting in?

96redformula7,
VR = variable resistor, .
No point in using axial resistors...

Soldering a 1kΩ VR in tuned @ max won't change the vGPU almost at all.

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Originally Posted by largon

96redformula7,
VR = variable resistor, .
No point in using axial resistors...

Soldering a 1kΩ VR in tuned @ max won't change the vGPU almost at all.

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Which resistor would I want to use for 1.25V? Is it something that I could go and pick up right now from radio shack?

Thanks for the help!

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Originally Posted by 96redformula7

Which resistor would I want to use for 1.25V? Is it something that I could go and pick up right now from radio shack?

Thanks for the help!

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It should be at Radio Shack. You can check online availability before you go there from the website. It costs $2.69, look up "potentiometer" VR search won't find it.

I preset mine at 530 ohms before having an electrical engineer do it for me. Yeah I cheated. :up: He had a pair of magnifying goggles so it was easy. I had him put it at the top of the card and run wires to the solder points so it is easy to adjust while in the case. Preset it with a dmm before having it soldered. 530 ohms gave me 1.16 volts. Just adjust from there...turn 1/8 turn and recheck and repeat and artifact check/check temps until you get where you want it. If you set it up like the pictures it should be counterclockwise for higher voltage/less resistance and clockwise for lower voltage/higher resistance.

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Originally Posted by JKDC

It should be at Radio Shack. You can check online availability before you go there from the website. It costs $2.69, look up "potentiometer" VR search won't find it.

I preset mine at 530 ohms before having an electrical engineer do it for me. Yeah I cheated. :up: He had a pair of magnifying goggles so it was easy. I had him put it at the top of the card and run wires to the solder points so it is easy to adjust while in the case. Preset it with a dmm before having it soldered. 530 ohms gave me 1.16 volts. Just adjust from there...turn 1/8 turn and recheck and repeat and artifact check/check temps until you get where you want it. If you set it up like the pictures it should be counterclockwise for higher voltage/less resistance and clockwise for lower voltage/higher resistance.

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Fantastic! Thank you.

Is the ~1.3V OVP for idle or under load?

Or does it vary around?

p.s. The Radioshack item you are looking for is a 1k-Ohm * 15 Turn Cermet Potentiometer

Item: 271-342 on front (I think this is it), and 271-0342 above serial on back

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Originally Posted by Hazaro

Fantastic! Thank you.

Is the ~1.3V OVP for idle or under load?

Or does it vary around?

p.s. The Radioshack item you are looking for is a 1k-Ohm * 15 Turn Cermet Potentiometer

Item: 271-342 on front (I think this is it), and 271-0342 above serial on back

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Alright, Thanks!

some mixed responses here

does anyone have a way to bypass OVP so far

and people watercooling without full blocks

what are you putting heatsinks on
PHOTOS mandatory here or ban/ :D

OVP is at 1.30v idle and 1.35v load. Actually it kicks in at 1.35v so a 1.30v idle setting will trigger it when it is loaded. The card adds .05v between idle and load. All Radio Shacks near me had the Cermet 15 turn pot. but I did get the last one in my town. :D

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Originally Posted by JKDC

OVP is at 1.30v idle and 1.35v load. Actually it kicks in at 1.35v so a 1.30v idle setting will trigger it when it is loaded.

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Thanks for the clarification. Anyone else to verify if they want to look at some more pretty blue/black screens? :D

My circuitwriter is due to ship Monday, hope it gets here before thanksgiving, otherwise it will be a while.

Gonna probably pick up a DMM at sears too, and maybe buy some gel super glue :yepp:

I just bought a 25W soldering iron, but have a feeling I need to return it to get a lower powered 15W. I have soldered before, but with a clunky gun shaped one. So I have to get some practice in on some old PCB's. Is Silver-Bearing Solder with Rosin Core alright to use for the VMod?

Thanks again guys.

Definitely go w/ the 15W. I'd go w/ standard rosin-core solder. That silver stuff may have a high melting temperature. I could be wrong, though.

I will stop back by radio shack tomorrow and get it exchanged. Thanks

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Originally Posted by GoldenTiger

The stock vGPU on these is 1.1v, I wouldn't adjust it to 1.4 off the bat as a "safe" voltage if I were you :). You can cause damage to the chip, and with these, you can't just lower it back down to fix it like with a CPU usually. You will *definitely* need a beefy after-market cooler for a voltmod on these, the stock cooler can handle some overclocking but runs borderline scorching when doing so, let alone volt-modded. The HR03 would be an excellent cooler (make sure it's the NON-plus version, the plus one *doesn't mount* on these cards), just be aware it takes up a few slots. I'm personally trying a pair of Thermaltake ND1's, which are coming in with my two cards tomorrow:

Picture of it mounted on a 7900GT (Thermaltake ND1):

http://img463.imageshack.us/img463/4...1062xs1wf3.jpg

These should cool well for me :D, assuming they fit (which it looks like they will, but I can confirm tomorrow).

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anybody confirm yet if Palit (supposedly 3-phase), has same volt-mod, and responds better to OVP?

warm ripe memories of 7900GT..
everybody wanted to max the juice, but too cheap to upgrade cooling.

btw: miss those good old days when you could dial in exactly voltage you wanted. XFX 7900GT + dip switch ~ 2 solid months of tweaking fun.

Just got a BFG 8800GT from best buy right now $250 on sale. Expect it to be volt modded soon.

Do I have to get a Multimeter or can I just put on the 1k ohm 15 turn potentiometer straight on? The screw is how it came inside the package from radioshack.

96redformula7,
There's no way to know what vGPU you end up with without a DMM.
Besides, a DMM is very useful in general.