Lenovo ThinkPad X390, Hardware Maintenance Manual, Page: 66 / 108

• 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, go to
https://support.lenovo.com/
partslookup .
• It is recommended to use new screws.
• It is recommended to use each screw only once.
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.
Notes:
• Ensure 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 that torque screwdrivers are calibrated correctly following country specifications.
Retaining serial numbers
This topic provides instructions on the following:
• “Restoring the serial number of the system unit” on page 60
• “Retaining the UUID” on page 61
Restoring the serial number of the system unit
When the computer was manufactured, the EEPROM on the system board was loaded with the serial
numbers of the system and all major components. These numbers need to remain the same throughout the
life of the computer.
If you replace the system board, you must restore the serial number of the system unit to its original value.
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X390 Yoga Hardware Maintenance Manual