Test the LVC Power Supply or Communications Adapter

Current Based Systems have an LVCV2 power supply

Reference: Testing an LVCV2 Power Supply 

Voltage Based Systems have a Communications Adapter, ensure it is passing the proper 48v to the driver board.

If the power supply is not putting out the proper voltage per the above article, test the bridge rectifier.

Reference: Testing a Bridge Rectifier 

Once input powers been verified and restored if necessary if the sign still will not illuminate

• Inspect the LED boards that are mounted on the mounting brackets. Cycle the power to the sign remotely or by using the optional isolating safety switch on the sign. If there is a fault with an individual LED board, all the LEDs should light up and then shut down within a second. The malfunctioning LED board will have an illuminated red LED directly on the circuit board as an indication that it or the driver circuit has malfunctioned.
  
  • To isolate the malfunction, remove the end loop plug from the end of the LED circuit where the red light was observed. Disconnect that string of LED boards from the driver and insert the end loop plug in its place on the driver. Cycle the power again and observe whether all remaining lights in the sign illuminate normally.
    • If all the lights remain on normally, there is a problem with a LED board on the string that was disconnected. Power off the sign, replace the bracket with the malfunctioning LED board, return the end loop to the OUT plug, and connect the LED bracket circuit to the driver again. Power on the sign, verify normal operation, and take the affected bracket back to the shop to isolate the indicated LED board for replacement. Instructions for replacing the LED board are on the following page.
    • If all the lights go out again and the red light appears on the remaining string plugged into the driver, then the driver needs to be checked. Power off the sign, unplug the power cable that runs from the power control module (PCM) to that driver, cycle the power to the sign, and confirm the other lights and driver circuits in the sign remain lit. If so, the disconnected driver needs to be replaced and the strings of LEDs connected to the new driver to confirm their operation.
    • Reference: Light Engine Replacement 

• Swap test the driver board
  • If the light engines don't seem to be the issue swap the driver board with a donor system or replacement part and test again
  • With the sign powered down, plug in the driver circuits individually and power on the sign to confirm their individual operation. If another driver circuit is found to be causing shut down, repeat the previous steps to isolate the cause.
    IMPORTANT: DO NOT PLUG DRIVER CIRCUITS INTO AN ENERGIZED LVC POWER SUPPLY WHEN TROUBLESHOOTING!
  • Reference: Driver Board Replacement 

• Check harnesses and end loops for damage, replace as necessary.  
• If the sign is not illuminating on all steps, most of the time the issue is an undersized isolation transformer. Verify you have the proper size isolation transformer to power the sign.