Vcore and Vdimm mod
Here’s the voltage mods for the Shuttle NForce 3 A64 motherboard.
Firstly, for Vcore, locate the IC chip shown in the picture near the socket.
Its the ISL6559 chip. Connect a 20K ohms variable resistor to pin 10. The other end of the VR is to be connected to a grounded
spot. Start with maximum resistance and tune downwards to increase Vcore.
For Memory Voltage, locate IC chip RT9202 as shown. Connect a 2.2K VR from pin
6 to ground. Set it to maximum resistance and slowly tune down to increase voltage.
Take note that there is virtually no cap on the VDimm here. You can go as high
as well over 4v as it is derived from the 5V line instead of the usual 3.3v
I have mine set so that maximum is 3.82v in bios, 3.64v is my sweet spot.
With 3.64 Vdimm, I hit 280Mhz FSB 1:1 fastest timings. This is the FSB cap of the beta bios from Shuttle. The beta bios allows some memory timings adjustments and up to 280Mhz FSB.