Dell Inspiron 17R 5720 Owner's Manual page 76

Procedure
NOTE: Your computer's Service Tag is stored in the system board.
You must enter the Service Tag in the BIOS after you replace the
system board.
NOTE: Before disconnecting the cables from the system board, note the location
of the connectors so that you can reconnect them correctly after you replace the
system-board assembly.
1 Close the display and turn the computer over.
2
Disconnect the subwoofer cable from the system-board connector.
1 subwoofer cable routing
76
| System Board
1
2 subwoofer cable
2