Lenovo IdeaPad U550 User Manual page 54

Chapter 3. Using the Internet
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Push the SIM card in until you hear a click, and then pull the SIM card out.
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Put the battery back in place, turn the computer over again, and
reconnect the cables.
Note: Never insert or remove the SIM card while the computer is on. Doing so may
cause permanent damage to the SIM card as well as the SIM card reader.
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