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Intermittent problems
Intermittent system hang problems can be due to a variety of causes that have
nothing to do with a hardware defect, such as cosmic radiation, electrostatic
discharge, or software errors. FRU replacement should be considered only when a
problem recurs.
When analyzing an intermittent problem, do the following:
1. Run the diagnostic test for the system board in loop mode at least 10 times.
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 29.)
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 find 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
46 ThinkPad T400 and R400Hardware Maintenance Manual