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