Dell Inspiron 14z (1470, Mid 2009) - Manual (Page 77)

System Board 77
NOTE: After you have replaced the system board, type the computer’s Service Tag
into the BIOS of the replacement system board.
21 Enter the service tag. See "Entering the Service Tag in the BIOS" on
page 77.
Entering the Service Tag in the BIOS
1 Ensure that the AC adapter is plugged in and that the main battery is
installed properly.
2 Turn on the computer.
3 Press <F2> during POST to enter the system setup program.
4 Navigate to the Security tab and type the service tag in the Set Service Tag
field.