Lcd Built-In Self Test (Bist); System-Diagnostic Lights - Dell Inspiron 14 3420 Service Manual

How to invoke L-BIST Test:
1. Press the power button to start the system.
2. If the system 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 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 PC settings.
When you notice screen abnormalities like flickering, distortion, clarity issues, fuzzy or blurry image, horizontal or vertical lines,
color fade etc., it is always a good practice to isolate the LCD (screen) by running the Built-In Self Test (BIST).
How to invoke 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 D key and Power on the laptop to enter LCD built-in self test (BIST) mode. Continue to hold the D key, until
the system boots up.
5. The screen will display solid colors and change colors on the entire screen to white, black, red, green, and blue once.
6. Carefully inspect the screen for abnormalities (any lines, fuzzy color or distortion on the screen).
7. At the end of the last solid color (red), the system will shut down.
NOTE: Dell SupportAssist Pre-boot diagnostics upon launch, initiates an LCD BIST first, expecting a user intervention
confirm functionality of the LCD.

System-diagnostic lights

This section lists the system-diagnostic lights of your Inspiron 14 3420.
Table 7. System-diagnostic lights
Blinking pattern
Amber
1
1
2
2
2
Solid
54 Troubleshooting
White Problem description
1 Unsupported (non-Dell)
4 Hinge cable OCP diagnostic
for LCD and camera power
4
7 LCD cable detects failure
8 Panel power diagnostic
- Dead battery cannot turn on
battery
Memory failure LED
Suggested resolution
Replace a new battery.
Reassemble the hinge cable or
replace a new cable.
Replace the system board.
Reassemble the LCD cable or
replace a new cable.
A/B swap to check panel or
system board damage, and
then replace the new one.
Notify user to charge the low
battery capacity until system
can turn on.