IBM ThinkPad A21m, Hardware Maintenance Manual

Page: 61 / 158

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
You are here because the diagnostic tests did not identify
which adapter or device failed, wrong devices are installed,
a short circuit is suspected, or the system is inoperative.
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 35.)
1. Power 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-IBM devices
b. Devices attached to the port replicator
c. Printer, mouse, and other external devices
d. Battery pack
e. Hard-disk drive
f. External diskette drive
g. DIMM
h. CD-ROM and diskette drive in the UltraslimBay
i. PC Cards
4. Power on the computer.
5. Determine whether the problem has changed.
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
Symptom-to-FRU index
ThinkPad A20m/p, A21m/p and A22m/p
55