HP EliteDesk 800 G1 Tower Service Manual page 170

If using a new heat sink, go to step 3.
1.
If reusing the existing heat sink, clean bottom of the heat sink and apply the thermal material
provided in the spares kit to the top of the processor.
2.
Position the heat sink atop the processor.
3.
If using a new heat sink, remove the protective covering from the bottom of the heat sink and
place it in position atop the processor.
4.
Secure the heat sink to the system board and system board tray with the 4 captive screws.
CAUTION:
an X) to evenly seat the heat sink on the processor. This is especially important as the pins on the
socket are very fragile and any damage to them may require replacing the system board.
158 Chapter 7 Removal and replacement procedures: Ultra-slim Desktop (USDT)
Heat sink retaining screws should be tightened in diagonally opposite pairs (as in