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2. If no error is detected, do not replace any FRUs.
3. If any error is detected, replace the FRU shown by the FRU code. Rerun the test to verify that no
more errors exist.
Undetermined problems
If the diagnostic tests did not identify the adapter or device that has failed, if wrong devices are installed,
or if the system simply is not operating, follow these procedures to isolate the failing FRU (do not isolate
FRUs that have no defects).
Verify that all attached devices are supported by the computer.
Verify that the power supply being used at the time of the failure is operating correctly. (See “Power system
checkout” on page 32.)
1. Turn off the computer.
2. Visually check each FRU for damage. Replace any damaged FRU.
3. Remove or disconnect all of the following devices:
a. Non-ThinkPad devices
b. Devices attached to the docking station or the port replicator
c. Printer, mouse, and other external devices
d. Battery pack
e. Hard disk drive
f. External diskette drive or optical drive
g. DIMM
h. Optical disk or diskette in the internal drive
i. PC Cards
4. Turn on the computer.
5. Determine whether the problem has been solved.
6. If the problem does not recur, reconnect the removed devices one at a time until you nd the failing FRU.
7. If the problem remains, replace the following FRUs one at a time (do not replace a nondefective FRU):
a. System board
b. LCD assembly
44 ThinkPad T520, T520i, and W520 Hardware Maintenance Manual