Dell Precision T3400 (Late 2007) - Manual (Page 253)

Adding and Replacing Parts
253
3 Loosen the two captive screws on each side of the heat-sink assembly.
CAUTION:
Despite having a plastic shield, the heat-sink assembly may be very
hot during normal operation. Ensure that the assembly has had sufficient time to
cool before you touch it.
4 Rotate the heat-sink assembly upward, and remove it from the computer.
5 Place the heat-sink assembly on its side in a safe place.
6 Disconnect the system fan cable from the system board.
1 heat-sink assembly 2 captive screw housing (2)
1
2