Dell OptiPlex 7040 Owner's Manual page 21

4. To remove the PSU:
a. Disconnect the power cable from the system board [1] [2].
b. Lift the cables away from the computer [3].
c. Remove the screws that secure the PSU to the computer [4].
5. Press the blue release tab [1], slide the PSU and lift it away from the computer [2].
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