HP rp5800 Reference Manual page 32

Figure 2-22
To install a Powered Serial Port expansion card:
1. Remove/disengage any security devices that prohibit opening the computer.
2. Remove all removable media, such as compact discs or USB flash drives, from the computer.
3. Turn off the computer properly through the operating system, then turn off any external devices.
4. Disconnect the power cord from the power outlet and disconnect any external devices.
CAUTION:
as long as the system is plugged into an active AC outlet. You must disconnect the power cord
to avoid damage to the internal components of the computer.
5. If the computer is on a stand, remove the computer from the stand.
6. Remove the computer access panel.
26 Chapter 2 Hardware Upgrades
Removing the Powered Serial Port Caps
Regardless of the power-on state, voltage is always present on the system board
ENWW