Lenovo ThinkPad T420si Hardware Maintenance Manual - Page 62

Intermittent problems, Undetermined problems, Non-ThinkPad devices

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Table 6. LCD-related symptoms (continued) Symptom or error • LCD screen unreadable. • Characters missing pixels. • Screen abnormal. • Wrong color displayed. Horizontal or vertical lines displayed on LCD. FRU or action, in sequence 1. See important note for "LCD-related symptoms." 2. Reseat all LCD connectors. 3. LCD assembly. 4. System board. LCD assembly. 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 42.) 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 56 Hardware Maintenance Manual

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Table 6. LCD-related symptoms (continued)
Symptom or error
FRU or action, in sequence
•
LCD screen unreadable.
•
Characters missing pixels.
•
Screen abnormal.
•
Wrong color displayed.
1.
See important note for “LCD-related symptoms.”
2. Reseat all LCD connectors.
3. LCD assembly.
4. System board.
Horizontal or vertical lines displayed on LCD.
LCD assembly
.
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 42.)
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
56
Hardware Maintenance Manual