HP Pro 3400 Maintenance And Service Manual page 127

4. Disconnect the cable from the system board (1), lift the fan sink from atop the processor (2) and
set it on its side to keep from contaminating the work area with thermal grease.
When reinstalling the fan sink, make sure that its bottom has been cleaned with an alcohol wipe and
fresh thermal grease has been applied to the top of the processor.
CAUTION: Fan sink retaining screws should be tightened in diagonally opposite pairs (as in an X)
to evenly seat the heat sink on the processor to avoid damage that could require replacing the system
board.
Failure to install the fan duct may cause the computer to overheat.
Fan Sink 117