Compaq 247320-003 - Deskpro 4000 - 5166 Model 2500/CDS Reference Manual page 127

The removable expansion board cage allows quick removal of
expansion boards, without disconnecting the cables attached to
the connectors on the expansion boards, and without the use of
tools. With the expansion board cage removed from the chassis,
you can easily access the system board.
To remove the expansion board cage, follow these steps:
1. If you have locked the Smart Cover Lock, use Computer
Setup to unlock the lock.
For more information about Computer Setup, refer to
Chapter 8, "Using Compaq Utilities."
2. Turn off the computer and any external devices.
3. Disconnect the power cord from the power outlet.
4. Remove the side panel.
5. Turn the minitower on its side, with the open side up.