NEC Express5800 series User Manual page 209

14.
Make sure that the heat sink is installed in parallel with the mother board.
IMPORTANT:
If the heat sink is not in parallel with the mother board, remove the
heat sink once and then install it again.
The heat sink may not parallel with the mother board due to the
following causes:
– The heat sink is installed on the CPU incorrectly.
– One or both of the heat sink clips is hung on the retention tab
incorrectly.
Do not hold the fixed heat sink to move the CPU blade.
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