Dell OptiPlex 9020 All In One (Mid 2013) - Manual (Page 35)

4. Press and push down the screws that are connected to the system board.
5. Remove the heat sink from the system board.
Installing the Heat Sink (Graphics Card)
1. Place the heat sink on the system board.
2. Press the screws to lock the heat sink to its position.
3. Connect the fan cable.
4. Install:
a) system board
b) power-supply fan
c) converter board
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