Dell OptiPlex 9020 (Mid 2013) - Manual (Page 29)

4. Remove the screws that secure the system board to the chassis.
5. Turn the hex screw counter clockwise and remove from the system board.
6. Remove the system board from the chassis.
Installing the System Board
1. Align the system board to the port connectors on the rear of the chassis and place the system board in the chassis.
2. Tighten the screws securing the system board to the chassis.
3. Connect the cables to the system board.
4. Install the:
a) power supply
b) expansion card(s)
c) heat sink assembly
d) memory
e) drive cage
f) optical drive
g) front bezel
h) cover
5. Follow the procedures in After Working Inside Your Computer .
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