Not that I've ever paid much attention to chip related matters, but I seem to remember that the D0 wire is essential for the purposes of getting the console to boot off the BIOS in the modchip.
Most hacked BIOSes change the flubber-sequence animation displayed on startup. If your boot sequence (
this) is the same regardless of how you're setting the switches, then odds are your modchip is currently non-functional.
