Have you verified the usual things, like making sure there is a
terminating resistor pack on the last drive in the chain? You've got the
drive select jumpers correctly set? What about the two data cables? 0
going to drive 0 and 1 going to drive 1? Does the control cable have the
correct twist to it? (afaik, the control & floppy cables had the same
number of lines, but the twist was different between them)
g.