Diagnosing LCD Problems

If you are experiencing problems with the LCD display, there are a few checks you can make to diagnose the problem. For example, it can be useful to determine whether the problem is the LCD panel or the backlight.

Known Problems

Backlight Remains Off

If the backlight remains off after booting, this can mean that either the board is running an old kernel, using the wrong device tree binary (dtb), or that the backlight itself is not connected. Follow the procedure below to diagnose which of these possible causes is the problem.

Stripes Along the Display Length

If the backlight is on and the display shows stripes parallel to the longest edge of the screen, the fault is probably due to an old kernel and display driver. Follow the procedure below, paying special attention to the first step.

Procedure

As a general guide, the following steps can be diagnose and cure the problem:

  1. Check that you are running an up-to-date kernel.

    Log in to the development board and type the following at the command line:

    uname -v
    

    You should see output like the following:

    #1 SMP PREEMPT Wed Feb 20 14:38:03 PST 2019
    

    Generally, kernels with a date later than this should have a working driver for the display panel.

    The simplest solution is to reflash the software on the board – see Flashing eMMC for instructions.

  2. Check the ribbon cable.

    The ribbon cable should be inserted squarely into the J1202 connector on the board. If it is inserted at an angle, perhaps due to movement of the panel, then it needs to be reinserted properly. Power down the development board before attempting to reinsert the cable.

    The location of the LCD ribbon cable connector (click to enlarge)

    The location of the LCD ribbon cable connector

  3. Use a spotlight to check the LCD display.

    If the backlight is off, it can be difficult to check that the LCD display itself is working. However, if you shine a spotlight onto the end of the panel next to the USB connector, you should be able to see faint arrows similar to these:

    ../../../_images/arrows.png

    Swiping the screen should cause the arrows to move and/or disappear.

If none of these checks result in an obvious cause, please get in touch.