HP TC4400 - Manual (Page 144)

Removal and Replacement Procedures
Maintenance and Service Guide 5–61
3. Disconnect the modem cable from the two connectors 1 on
the system board.
4. Remove the two Phillips PM2.0×4.0 screws 2 that secure the
modem board to the system board.
5. Lift the right side of the modem board 3 to disconnect it
from the system board.
6. Remove the modem board.
Removing the Modem Board
Reverse the above procedure to install the modem board.