Apple Video System - Manual (Page 39)

5 If there are security screws on the vertical plate on the back
of the computer, remove them with a screwdriver.
6 Unplug the power cord from your computer.
Remember: Don’t walk around the room until you have
finished installing the card and closed the computer. Move
the logic board as little as possible while it’s outside the
computer.
7 Swing the handle out from its storage position, then grasp
the handle and gently but firmly pull it toward you.
The vertical plate and the logic board to which it’s attached
slide all the way out of the computer.
Pull out the
logic board.
If there are security screws, remove both screws from the vertical plate.
33 Installing the Card and Software and Connecting Video Equipment