Tuesday, June 11, 2013

Digital Signage How To: Basic LED Sign Troubleshooting and Logic

- Scott Hofheins

One of our main goals for this blog is to be a resource to the industry, regardless of the manufacture. In keeping with that spirit I would like to go through some basic LED troubleshooting principles to help those who are new to LED signs, or have found themselves with a broken sign or a manufacturer who is difficult to work with.

Although the quality and design approaches are different between manufacturers, there are some general concepts that most outdoor LED sign systems will follow. They include basic operating components working together to create a full outdoor LED sign system. Deacon has a great post with some good notes on making sure you’re getting quality components for these systems.  

Basic Components
  • Controller: This is the brain of the LED sign and is typically the junction point for the communications, temp/light sensors, and video input and output for the entire sign.
    • PC Based (IPC): These are typically internal (sometimes external) industrialized computers running a secure operating system. They are more powerful and tend to give a bit more flexibility to the system with regards to video display, troubleshooting and customization.
    • Embedded Controller: These will look more like a circuit board and are typically used in systems geared for static text and images. Many will play animations and some video, but the frame rate and storage space is limited.
  • Video Board: This converts the video signal from the controller into a readable format for the sign hardware. This board is sometimes combined with an embedded controller, but it usually separated on an IPC based system. Terminology can include: DVI Board and Sender Card.
  • Logic Board: These translate the video signal from the Video Board, to the individual LED modules on the sign, usually in rows or columns depending on the manufacturer. These are sometimes combined with embedded controllers on value systems. Terminology can include:  Turbo Boards, Receiver Cards, Hub Cards, Row Boards, and Ribbon Boards.
  • LED Modules: These are the actual panels of LED’s that make up the entire sign. They can range is size from 8x8 pixels to 16x16 pixels and larger depending on the pixel pitch (how close the pixels are to each other). The rear of the Modules will typically have the power and data connectors integrated. Terminology can include: Driver Boards, Tiles and LED Panels.
  • Power Supplies: These power the internal hardware for the LED sign. They will usually take in AC voltage, and output DC voltage to the components. They will typically power more than one component or LED module.
  • Temperature Probe: These are typically used to get outside temperature readings to display on the sign. These have been standard equipment on LED signs since the early days, but are used less frequently now as owners focus more on content and targeted advertising.They vary in appearance, from simple metal probes, to white “finned” apparatuses.
  • Communication Devices: Many signs use secured Wireless communication devices these days, but many still use traditional wired solutions like Fiber Converters, and hardwired Cat5/6 Ethernet cable. 

Troubleshooting LED Signs.

Follow the Data Chain
LED signs rely on a certain amount of “daisy chains” to get data from one component to the next. Generally speaking, it goes something like this:
User’s Computer --- Communication Device  on Building --- Communication Device on the Sign --- Sign Controller --- Video Board --- Logic Board (These are daisy chained to other Logic Boards across the sign) --- Rows or Columns of LED Modules Daisy Chained together.
Keep it Simple
Look at your symptoms, and find a logical place to start ruling out causes of the issue. For example, if the sign has a module out, you wouldn’t start testing the communication devices. You would start looking at the LED sign hardware (LED Modules, Data cables, etc...). 

Make the Issue Move
When you are physically troubleshooting components, you want to either fix the issue or make it move. If you can make it move then you can isolate the component and replace or repair it to fix the issue.

Electronic devices sometimes get locked up and require a reboot to get going again. Cycling power to the sign can sometimes fix issues. However, you shouldn’t have to do this constantly. If so, then look for the root cause of the freeze ups.

Specific Issues with LED Signs

Sign is Blank
  • Verify Sign is powered within specs.
  • Check the other side. If it’s working you may have a communication or power issue between the functioning side, and the blank side.
  • Check your schedule. Is content scheduled to be playing? An expired schedule is a common cause for a blank LED sign.  
  • Can you communicate to the display? If so, then you know the controller is working and you can check other parts of the system.
  • If it’s a PC controller can you log in and verify the “player” is running? If it’s an embedded system it may have some diagnostic features that will allow you to see if it’s physically playing data.
  • Check the Video Board. Is it getting power? Is it getting signal from the PC and sending it to the other components? Check the Data Cables.
  • Check the Logic Board, and make sure it’s getting power and data. Unless you have a looped system, a bad Logic Board at the beginning of the data chain can cause the rest of the sign to go blank.

One or More Sections of a Face Blank
  • Verify power is supplied for the first section not working.
  • Check the Hardware (DVI Board, Logic Board) that is responsible for the first section in the chain that is not working.
  • Check the power supplies in that same section.

One or more LED modules out or “scrambled”
  • Always start at the first module in data chain that is NOT working. Make sure it’s getting power, and getting data from the previous data source (LED Module or Logic Board).
  • Check the module next to it that IS working. Sometimes the output is bad, or the data cable between the two is bad. Swapping these boards can help isolate the issue.
  • If the module is getting data from the Logic Board, check the data ports and cable. Swapping cables will help determine if it’s a port on the Logic Board, LED Module, or just a bad cable.

Line or Linear Errors Across the Entire Sign.
  • Double check the content. Make sure your file doesn’t have errors.
  • Check the Logic Board. This is responsible for whole rows, or columns of LED Modules.
  • Check the first LED Module in the series. On a smaller sign, it may be sending bad data to the rest of the row or column.

Errors and Display Issues with the Entire Sign
  • Double check the content. Make sure your file doesn't have errors.
  • Check the Video Board. This board is responsible for the entire video signal to the rest of the sign. Make sure it’s getting good data from the controller, and good DC power from the power supply.
  • Check the controller’s video output. Sometimes a loose cable can cause video issues that will affect the entire sign.

Issues can seem complicated and difficult, but if you remember to think linear, keep it simple, and take a step by step approach you will find that they can be isolated relatively quickly. Even the best LED signs will have issues now and then, but remember the quality of the manufacturers design, components and support play a huge factor in how often this happens and how easy it is to fix when it does.


I hope this post has been informative and helpful. As usual, I welcome ALL constructive comments. Please feel free to comment and add anything I’ve missed, or additional tips you may have regarding this topic. Please visit www.vantageled.com for many other resources, white papers, and of course: Great looking LED Signs!

**All posts/thoughts/writings are strictly the viewpoint of me and me alone and do not reflect nor speak for Vantage LED’s beliefs, attitudes, thoughts, etc. unless specifically stated.


Barbara Roost said...

I'm not usually the one that manages our LED sign, as I'm incompetent with wires and machines and all. But our main guy is out of town, and the responsibility fell to me. You're right about keeping it simple. There were lines across the sign, and I was sure that something was horribly broken, but it was just an error in the file, like you said. I hope I don't have to do this again, but I will probably come to your post again if I do! Thanks for your help.

Barbara Roost | http://strictlyneon.net/

mikal shone said...

NICE post

Deacon Wardlow said...

Thank you. We appreciate you appreciating the post.

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