From MickeyMouse:

Solder a 15turn"multi turn" 250 ohm vr or 2 1k vr's in par. to these two points. "do not exceed a 500ohm vr as jumps are too great". the resistor is the circuit the solder pad is ground so feel free to use another ground instead of this tiny tiny solder pad..

7800vcore
http://img93.imageshack.us/img93/499/7800vgpu9nq.jpg

7800vcore mod area and read point
http://img36.imageshack.us/img36/4726/7800corea0kt.jpg