HP 520 Maintenance And Service Manual page 64

Lift the left side of the heat sink (3) and remove it.
3.
NOTE:
processor (1), the processor (2), and the heat sink (3) and (4) each time the heat sink is removed.
Reapply the thermal material when the heat sink is replaced. Thermal material is included with all
heat sink, processor, and system board spare part kits.
Reverse this procedure to install the heat sink.
56 Chapter 4 Removal and replacement procedures
The thermal material should be thoroughly cleaned from the surfaces of the video