Compaq 500B Microtower Supplementary Manual page 44

15 Set the computer upright.
16 Detach the four screws that connect the power supply
to the computer.
17 Use a screwdriver to press the latch at the bottom of
the power supply to release it.
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18 Pull the power supply back and tilt it out of the
computer.
Removing and Replacing a Power Supply