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3. If there is a failure with the system board, the battery status LED flashes one of the following error codes for 30 seconds:
Table 47. LED error codes
Blinking Pattern
Amber
2
2
1
2
4. If there is no failure with the system board, the LCD cycles through the solid color screens that are described in the
LCD-BIST section for 30 seconds and then turn off.
LCD Power rail test (L-BIST)
L-BIST is an enhancement to the single LED error code diagnostics and is automatically initiated during POST. L-BIST will check
the LCD power rail. If there is no power being supplied to the LCD (that is if the L-BIST circuit fails), the battery status LED
flashes either an error code [2,8] or an error code [2,7].
NOTE:
If L-BIST fails, LCD-BIST cannot function as no power will be supplied to the LCD.
How to invoke the L-BIST Test:
1. Press the power button to start the computer.
2. If the computer does not start up normally, look at the battery status LED:
● If the battery status LED flashes an error code [2,7], the display cable may not be connected properly.
● If the battery status LED flashes an error code [2,8], there is a failure on the LCD power rail of the system board, hence
there is no power that is supplied to the LCD.
3. For cases, when a [2,7] error code is shown, check to see if the display cable is properly connected.
4. For cases when a [2,8] error code is shown, replace the system board.
LCD Built-in Self-Test (BIST)
Dell laptops have a built-in diagnostic tool that helps you determine if the screen abnormality you are experiencing is an inherent
problem with the LCD (screen) of the Dell laptop or with the video card (GPU) and computer settings.
When you notice screen abnormalities like flickering, distortion, clarity issues, fuzzy or blurry image, horizontal or vertical lines,
color fade and so on, it is always a good practice to isolate the LCD (screen) by running the Built-In Self-Test (BIST).
How to invoke the LCD BIST Test
1. Power off the Dell laptop.
2. Disconnect any peripherals that are connected to the laptop. Connect only the AC adapter (charger) to the laptop.
3. Ensure that the LCD (screen) is clean (no dust particles on the surface of the screen).
4. Press and hold the D key and Power on the laptop to enter LCD built-in self-test (BIST) mode. Continue to hold the D key
until the computer boots up.
5. The screen displays solid colors and change colors on the entire screen to white, black, red, green, and blue twice.
6. Then it displays the colors white, black, and red.
7. Carefully inspect the screen for abnormalities (any lines, fuzzy color, or distortion on the screen).
8. At the end of the last solid color (red), the computer shuts down.
NOTE:
Dell SupportAssist Preboot diagnostics upon launch initiates an LCD BIST first, expecting a user intervention to
confirm functionality of the LCD.
White
1
8
1
4
Possible Problem
CPU Failure
LCD Power Rail Failure
TPM Detection Failure
Memory/RAM failure
Troubleshooting
161
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