Apple Mac Performa 640 series - Manual (Page 146)

Opening the computer
1 Shut down your computer by choosing Shut Down from the Special menu.
You can also press the Power key on the keyboard.
2 Unplug all the cables except the power cord from your computer.
Leaving the power cord plugged in helps protect the computer from damage
caused by electrostatic discharge.
IMPORTANT To avoid generating static electricity that may damage
components, do not walk around the room until you have completed the
installation of the expansion card or SIMM and closed the computer.
Additionally, move the logic board as little as possible while it is outside the
computer case.
3 Place your thumbs on the two tabs at the top of the back panel, and press down.
4 Pulling gently, swing the panel down, and slip it out.
Remove the back panel.
138 Appendix B