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Attention: The drive startup sequence in the computer you are servicing may have been changed. Be
extremely careful during write operations such as copying, saving, or formatting. If you select an incorrect
drive, data or programs can be overwritten.
If your computer is shipped with an mSATA drive and a solid state drive or hard disk drive, the mSATA drive
will be seen as hard disk 0 in the system, and assigned drive C:. The solid state drive or hard disk drive will
be seen as hard disk 1, and assigned drive D:. The mSATA drive is installed in the wireless WAN card slot of
the computer. The Lenovo preloaded software is installed on the mSATA drive.
Always try to run a low-level format before replacing a hard disk drive. This will cause all customer data on
the hard disk to be lost. Be sure that the customer has a current backup of the data before doing this task.
Attention: The drive startup sequence in the computer you are servicing may have been changed. Be
extremely careful during write operations such as copying, saving, or formatting. If you select an incorrect
drive, data or programs can be overwritten.
Important notice for replacing a system board
Some components mounted on a system board are very sensitive. Improper handling of a system board can
cause damage to those components, and may cause a system malfunction.
Attention: When handling a system board:
• Do not drop a system board or apply any excessive force to it.
• Avoid rough handling of any kind.
• Avoid bending a system board and hard pushing to prevent cracking at each BGA (Ball Grid Array) chipset.
How to use error message
Use the error codes displayed on the screen to diagnose failures. If more than one error code is displayed,
begin the diagnosis with the rst error code. Whatever causes the rst error code may also cause false error
codes. If no error code is displayed, see whether the error symptom is listed in the Symptom-to-FRU
Index for the computer you are servicing.
24 ThinkPad T420 and T420i Hardware Maintenance Manual