Dell OptiPlex 9020 (Mid 2013) - Manual (Page 28)

Installing the System Board
1. Align the system board to the port connectors and place the system board in the chassis.
2. Tighten the screws to secure the system board to the chassis.
3. Connect all the cables to the system board.
4. Install:
a) I/O panel
b) WLAN Card
c) memory
d) processor
e) heat sink assembly
f) power supply
g) drive cage
h) front bezel
i) cover
5. Follow the procedures in After Working Inside Your Computer .
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