NEC EXPRESS 5800 User Manual page 263

6. Push the CPU lightly to the socket, and push down the lever to secure the CPU.
Put the heat sink on CPU.
7.
NOTE: Be aware of direction of heat sink. The bottom of the heat sink has
L-shaped groove. Put the heat sink so that the groove fit the lever and
plastic part of the socket.
Groove
Plastic portion
Upgrading Your System 7-25
Plastic portion
Top View
Heat sink
Groove