Lenovo ThinkPad L421 Hardware Maintenance Manual - Page 61
FRU replacement notices, Screw notices
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Chapter 7. FRU replacement notices This chapter presents notices related to removing and replacing parts. Read this chapter carefully before replacing any FRU. Screw notices Loose screws can cause a reliability problem. In the ThinkPad notebook computer, this problem is addressed with special nylon-coated screws that have the following characteristics: • They maintain tight connections. • They do not easily come loose, even with shock or vibration. • They are harder to tighten. Do the following when you service this machine: • Keep the screw kit in your tool bag. For the part number of the screw kit, see "Miscellaneous parts" on page 143. • It is recommended to use new screws. • It is recommended to use each screw only once. • Use a torque screwdriver if you have one. Tighten screws as follows: • Plastic to plastic Turn an additional 90 degrees after the screw head touches the surface of the plastic part: • Logic card to plastic Turn an additional 180 degrees after the screw head touches the surface of the logic card: • Torque driver If you have a torque driver, refer to the Torque column in the screw information table for each step. • Make sure that you use the correct screw. It is recommended to use new screws for replacements. • If you have a torque screwdriver, tighten all screws firmly to the torque specified in the screw information table for each step. • Ensure torque screw drivers are calibrated correctly following country specifications. © Copyright Lenovo 2011, 2012 55