Dell OptiPlex 3070 Small Form Factor Service Manual page 54

a) Disconnect the CPU power cable from the system board [1].
b) Unroute the power cables from the retention clips on the chassis [2].
4. To remove the PSU:
a) Remove the 3 screws that secure the PSU to the system [1].
b) Disconnect the system power cable from the connector on the system board [2].
c) Lift the cables away from the system [3].
d) Press the blue release tab [4] at the rear end of the PSU unit, slide the PSU and lift it away from the system [5].
54 Removing and installing components