Lenovo ThinkPad X390, Hardware Maintenance Manual, Page: 46 / 108

1. Ensure that the computer is connected to ac power. Then, press the power button for about seven
seconds to turn off the computer.
2. Press Fn, left Ctrl, and the power button at the same time. If the computer displays five solid colors in
sequence across the entire screen, it indicates that the LCD functions normally.
3. The test lasts for about 20 seconds and then exits automatically. You also can press the power button to
exit the test.
Table 4. LCD-related symptoms
Symptom or error FRU or action, in sequence
No beep, power-on indicator on, and a blank LCD during
POST. 1. Run LCD Self Test .
2. Replace the system board.
• LCD backlight not working.
• LCD too dark.
• LCD brightness cannot be adjusted.
• LCD contrast cannot be adjusted. 1. Reseat the LCD connectors .
2. Replace the LCD assembly.
3. Replace the system board.
• 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. Replace the LCD assembly.
4. Replace the system board.
Horizontal or vertical lines displayed on LCD. Replace the 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 28.
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
e. Storage drive
f. External diskette drive or optical drive
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X390 Yoga Hardware Maintenance Manual