NEC POWERMATE ES 5200 Manual page 159

If the system board is aligned correctly, you might need
to push the outside edges of the board to fully seat it into
the connector on the riser board.
Check the position of the chassis latch. The system board
is secured when the latch is parallel with the outside edge
of the board.
Secured position of latch — small desktop
A – Rail
B – Latch Closed
5. Replace the cover (see "Replacing the Small Desktop or
Desktop Cover").
5-44 Installing Options
C – Edge of Chassis
D – Edge of System Board