Apple Performa 6400/180 - Manual (Page 105)

Take Apart Top Cover - 8
2 Slide the top cover back
about one-half inch.
3 Lift the top cover from
the computer.
Replacement Note:
Place
the top cover on top of the
chassis, about a half inch
from the front of the
computer. Slide the cover
forward until it is firmly in
place. Replace the captive
cover screw on the rear
panel.