Click below to see what I'm talking about. You will see that 3 wires stem from the modchip, 2 of which go on to solder points on the board and the third goes onto a little resistor.
But the fourth wire does not touch the modchip at all. It just links two solder points together, on the board. One end of this link wire goes onto a little resistor, the other onto a blank solder point.
Also, don't overlook the obvious. Make sure you are numbering the legs of the chip properly by using the top left hand corner leg as leg 1, if you hold the chip with the notch facing UPWARDS
http://www.maxking.com/psxmod.htm#9000
Hope this helps