Chapter 7. Fru Replacement Notices; Screw Notices - Lenovo THINKPAD L420 Hardware Maintenance Manual

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, 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.
• Each one should be used only once.
Do the following when you service this machine:
• Keep the screw kit (for the P/N, see "Miscellaneous parts" on page 153) in your tool bag.
• Always use new screws.
• 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 for each step.
• Make sure that you use the correct screw. If you have a torque screwdriver, tighten all screws firmly to the
torque shown in the table. Never use a screw that you removed. Use a new one. Make sure that all
of the screws are tightened firmly.
• Ensure torque screw drivers are calibrated correctly following country specifications.
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