Apple PowerBook Duo Dock (including Duo Dock Plus) - Manual (Page 37)

6 Pull the subassembly toward you until you feel it come to a stop.
It will move only a short distance. You’ll be able to feel a small gap under the
front ledge of the dock.
If the subassembly doesn’t seem to move, or if you can’t feel a gap under the
front ledge, the screws may not be loose enough. Turn them a few more times
and try again.
The subassembly is heavy, so before you continue with step 7, make sure that
you have enough room to put it down nearby after you lift it off the base.
31 Installing a NuBus Card