15. Follow the instructions from step 13 to step 18 in Removing the Top Cover.
16. Remove the heat sink (see Removing the Heat Sink).
17. Remove the processor module (see Removing the Processor Module).
18. Remove the I/O board (see Removing the I/O Board).
19. Disconnect the fan cable and AC-adapter connector cable from their connectors on the system board.
20. Remove the screw that secures the system board to the top cover.
21. Lift the system board off the top cover.
Replacing the System Board
1. Follow the instructions in Before You Begin.
2. Align the screw hole on the system board with the screw hole on the top cover.
3. Replace the screw that secures the system board to the top cover.
4. Connect the fan cable and AC-adapter connector cable to their connectors on the system board.
5. Replace the I/O board (see Replacing the I/O Board).