Apple PC Serial and Parallel Card - Manual (Page 43)

Opening the computer
1 Disconnect all the cables from the computer, except for the power cord.
Leave the computer plugged in for now, to ground it and protect its
components from static electricity damage.
2 Loosen the large screws on the back panel.
If you have a Power Macintosh 8500, there are four screws, one at each
corner of the back panel. If you have a Power Macintosh 9500, there are six
screws, one at each corner and two on the sides of the back panel. Do not
completely remove the screws or the back panel.
43 Installing the Card in a Power Macintosh 8500 or 9500