IBM NetVista A21 User Manual page 56

4. Remove the power supply and carefully lay it to the side.
5. To replace the power supply, reverse these steps.
Identifying parts on the system board
The system board, also called the planar or motherboard, is the main circuit board
in your computer. It provides basic computer functions and supports a variety of
devices that are IBM-installed or that you can install later.
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User Guide