Dell Precision 690 - Manual (Page 132)

6. If you do not have memory risers installed, lift to remove the memory fan from the fan support structure.
7. Remove the fan support structure or memory-riser support structure:
a. Remove the four screws that attach it to the system board.
b. Lift it from the computer.
8. Disconnect the speaker cable from the system board.
9. Disconnect the front fan and the card fan from the system board.
10. Unscrew the two screws that hold the processor and card fan case in place and lift it away from the computer.
These screws help to secure the system board in place.
1 screws (4)
2 graphics riser card
1 memory fan (only present on computers without memory riser cards)
2 fan support structure