http://img58.imageshack.us/my.php?image=775dualvcoremodio1.jpg]
[/URL]
I will try to find a better image of the area, this is just a hint. It is tested on 775 dual vsta, for sure does not work on 775 dual 880 pro because of different Vcore Power Supply. 4coreDual vsta looks the same as 775 dual vsta but I do not have any for checking.
CAUTION: This is a risky hardware mod, and guarantee of the board is lost by soldering on. If you proceed, you are doing the mod on your own risk, I can not be made responsible for any consequences of it or mistake in pictures and/or description.
The 100K is connected between the 2 points marked with red lines, and placed on the L6714 IC (somehow were the lines end). Both connection points are from not assembled components. For checking, point 1 should be connected with pins 21&22 (DROOP and FB in the image bellow) of L6714, pin 2 shall be connected to GND or case.
http://img53.imageshack.us/my.php?image=l6714hz6.jpg]
[/URL]
What could be important:
Never short the VR, check with ohmmeter that the pins used are the ones with maximum resistance !!! When adjusting move slowly to avoid voltage jumps !!!
1. Try to keep connection 1 as short as possible
2. Connection 2 is a GND point, but I think the one I pinpointed is less risky as possible noises.
3. Avoid big VR and long wires, it is a risk to make core voltage very noisy
4. It would be better to connect a Voltmeter in position to measure Vcore when first supplied such as to be able to immediately disconnect mains if too high voltage.
5.
This is not tested, is by operation description of the power controller: If too high voltage will be set (> ~1.8V), the core supply will immediately shut down. If so, turn of the PC by disconnecting mains, adjust the VR to higher value (so lower voltage) and connect again.
6. When trimming the VR avoid touching with your hand anything connected to wire 1, the supply may loose regulation!
7. Before soldering disconnect PC from main, better the monitor too, and touch briefly with the tip of the soldering iron a metal part of the case to avoid static charges. If you notice sparks touch again and DO NOT SOLDER if the sparks do not disappear.