Dar_T

GPU Over current protection Mod




High overclocks can increase the GPU's power consumption to a point that the built-in over current protection of the vGPU phase controller is triggered. OCP manifests as a sudden blackout during 3D load accompanied by a collapse of vGPU voltage to ~0 V. Reports indicate OCP activating at frequencies exceeding 850 MHz for GPU and 2 GHz for shaders respectively. Users with 2-phase GeForce 8800 GS and GT are more likely to encounter OCP compared to the owners of 3-phase GeForce 8800 GTS as higher number of phases means lower current flow per phase. Luckily, there is a way to push the OCP-trigger point by altering the resistance of certain capacitors lingering around Primarion PX3544 regulator chip. Note that reference design GeForce 8800 GS and GT cards have two "OCP capacitors" as these cards have a 2-phase vGPU regulation. The GeForce 8800 GTS 512MB on the other hand is a native 3-phase design and consequently has three "OCP capacitors".

Refer to the pictures above for a demonstration of the mod.

Default resistance measured across each of the surface mount capacitors is ~1.2 kΩ. In order to push further the OCP trigger-point this resistance needs to be lowered - this can be done by soldering resistors of appropriate values on top of the capacitors. Resistors rated at 4.2 kΩ should give enough headroom for most overclocks. Minimum recommended value for the added resistors is 1.2 kΩ. It is not advised to go below this value as these capacitors are also used for balancing the outputs of the vGPU phases and lower resistance only interferes with this function but yields no practical gains.

Note that OCP mod does not increase your overclock unless your card actually is limited by OCP:

* Sudden blackouts during 3D load accompanied by freezing/resetting
* Collapsing vGPU voltage

http://forums.techpowerup.com/showth...943#post684943

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First Mod: Acrylic Case Mod http://www.overclock.net/case-mod-wo...lue-black.html

maggotnumber666

I have a question if you guys wouldn't mind helping me with it. I'm about to do this mod tonight, but I already have my voltage bumped up through a bios mod to 1.2v at load. Will this mod still work with the changed bios in place or would I have to revert back to the original bios? I'm not really too savvy when it comes to resistors and capacitors etc, but without soldering it seems so easy :P

TheSubtleKnife

Hey Dar T, I knew that there were OVP chips on all of these cards, but i did not know that the limit was so low, because on the old G80's they were limited at like 1.5v...i'll look into trying this, seeing as i have those symptoms
Edit: maggotnumber666, yes, this mod will work fine with the modded BIOS

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Microx256

850Mhz? how come my card is at 870Mhz core stable.. it might be that i dont have the Reference design 8800GT PCB..

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maggotnumber666

Excellent. Thanks for the info! Will update later and I appreciate the prompt response TheSubtleKnife. Happy overclocking.

Dar_T

Thanks for looking into this Subtle. +

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First Mod: Acrylic Case Mod http://www.overclock.net/case-mod-wo...lue-black.html

Dar_T

After a few tests I found that my rig would shut of at 1.3v with two cards but will shut of at 1.4v with one card. Shouldn't it be the same??? ***??? I am now tending to believe that my psu isn't keeping up. Can anyone verify that my psu is up for the task? (in sigrig)

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First Mod: Acrylic Case Mod http://www.overclock.net/case-mod-wo...lue-black.html

Microx256

i can go up to 1.55V on my card, but for a short period only before my card starts heating up.. maybe even more, but i didnt dare to go higher up..

could also be that my card is not the Reference 8800GT board..

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Keeep Out

can someone please help me? both me and my friend are trying to do this volt mod (soderless) and we have been running into trouble. I am trying to do this on a GTS G92 and my friend on a GT. we both bought the same potentiometers, the one from radio shack in the description - 1k, and we have the same problems. we cannot get passed 1.17 volts no matter which direction we turn it. I tried (i prolly shouldn't have, but i did) to test it in windows stressing. it showed up around 1.2 for me under stress but i still cant go past that. am i suposed to go by what it shows under stress? any way to get it higher? either way I cant go past 795 still (just like on stock)

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Keeep Out Of Reach Of Children

whe3ls

i check your connections

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