Lenovo ThinkCentre M77 Hardware Maintenance Manual page 159

7. Remove the screw that secures the cover presence switch (intrusion switch) and remove the cover
presence switch from the chassis.
Figure 90. Removing the cover presence switch
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Chapter 9 Replacing FRUs (Machine Types: 1996, 1997, 2002, 2010, 2208, 2209, 2221, 2224, 2226, and 2227.)