Only Part of My LED Sign Is Working — One Side or Section Is Off
If only part of your LED sign lights up — for example, half of one side is on and the rest is off, or your sign is double-sided and only one side (or part of one side) works while the other remains completely dark — this guide will help you identify the cause and restore full operation.
This situation usually occurs when there is a break in communication between video/receiving cards or a loss of power at the point where the last working section ends. In some cases, a failed cable or video card may interrupt the link between connected modules or sides.
Before you begin, read all instructions carefully and gather the tools listed below.
Tools You Will Need
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3 mm Allen wrench – for removing front modules
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Ethernet cable (6 ft or longer) – for testing or bypassing connections
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#2 Phillips screwdriver – for replacing video cards or power supplies
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Optional: Multimeter – to confirm power delivery (consult an electrician if unsure)
Safety First
Always disconnect main power before removing modules or handling internal components.
If you are not comfortable using a multimeter or working near electrical components, consult an electrician or contact LED Sign City Support before proceeding.
Step 1: Observe the Symptom
Begin by noting exactly what part of your sign is working and what part is off.
For example:
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One side works completely, but the other side is off.
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One section of a side works, but the remainder is dark.
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Half of a side works while the other side is fully off.
Although it may appear that “one-third” or “half” of the sign is out, the actual cause is often a single receiving card or cable between cards that has failed.
Step 2: Understand the Layout of Your Sign
Each video (receiving) card can control up to 16 modules. Larger signs use multiple cards linked together to expand control.
Examples:
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A 4×4 sign may use one card.
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A 4×6 sign may use two cards.
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A 6×9 sign may use up to six cards, each controlling nine modules.
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An 8×12 sign may also use six cards, each controlling sixteen modules.
Knowing how your sign is structured helps you determine where the data link stops. The boundary between the working and non-working section is the most likely point of failure.
Step 3: Locate the Video and Controller Cards
The controller card (main control board) is typically located behind the first module on the left side of the sign.
The video or receiving cards are installed behind the modules in each section the controller communicates with.
For most signs up to 4 feet tall, the video cards are located along the bottom row of the sign.
Examples:
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A 6-foot-wide sign will usually have the controller behind module 1, and video cards behind modules 2 and 4
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A 4×8 sign will typically have the controller behind module 1, and video cards behind modules 2 and 5.
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As the sign grows larger, each video card continues this pattern — roughly one card per 3–4 modules.
If you have rear access, you can easily see the video cards mounted inside the cabinet. Each card is located directly behind the section where power and signal cables connect to the sign.
Step 4: Locate the Problem Area
Find the first module that is not working next to one that is working. Behind that module is the video card where the issue likely begins.
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Remove the module in front of that card using a 3 mm Allen wrench.
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Once the module is removed, restore power to the sign so that the card can be tested.
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Locate the test button on the card.
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With power on, press and release the test button twice and observe the screen.
Step 5: Interpret the Results
Scenario 1 – No Response
If nothing happens when you press the test button:
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Disconnect the Ethernet cables from the bottom of the card and press the test button again.
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If there is still no change, confirm that the card is receiving power:
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Look for a small LED indicator light on the card.
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Use a multimeter to check for approximately 5 V DC from the power supply.
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If the card has no power, inspect the power supply feeding it.
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Confirm that power to the sign is on.
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If power is reaching the supply but it is not outputting voltage, replace the power supply.
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If power is present and the test button still produces no image, replace the video card.
Scenario 2 – Screen Lights Up When You Press the Test Button
If the section responds each time you press the test button:
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Check that the Ethernet cables are fully connected and seated properly.
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If they are connected, the card may not be detecting a signal from the previous card.
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To confirm, remove the module in front of the last working controller.
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Use a direct Ethernet cable to connect Port 2 on the working card to Port 1 on the non-working card.
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If the dark section powers up, the original Ethernet cable or connector is faulty. Replace or bypass that cable.
If you cannot access the rear of the sign, you can route a new internal Ethernet cable between the cards by removing the modules in between and running a new line inside the cabinet.
If that resolves the issue, reinstall the modules. If not, replace the video card.
Step 6: Reassemble and Test
After replacing or reconnecting components:
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Reinstall any removed modules.
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Power the sign on.
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Send a test message from your software.
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Confirm that all sections display properly.
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Monitor the sign for 24 hours to confirm the fix is stable.
Cabinet Access Notes
Older cabinets typically open by unlatching locks at the bottom and lifting the screen forward.
Front-service cabinets have modules secured with screws around the perimeter.
When lifting a cabinet, inspect hinges and hydraulic lifts for wear or leaks. Lift slowly and evenly to prevent strain or damage.
Frequently Asked Questions
How do I remove a front-service module?
Use a 3 mm Allen wrench to loosen the screws at the corners of the module. Lift gently from the bottom and disconnect the power and data cables from the back before removing the module completely.
Can I use any Ethernet cable for testing?
Yes. Any Cat5e or Cat6 Ethernet cable will work for troubleshooting as long as it’s at least 6 feet long and in good condition.
What if my power supply light is off?
Confirm that the main power to the sign is turned on. If it is, and the light remains off, the power supply has failed and should be replaced.
How can I tell which module covers a video card?
For most signs under 4 feet tall, the cards are located along the bottom row. The controller is behind the first module on the left, and the next video cards follow every 3–4 modules across the bottom.
Is it safe to test the sign with power on?
Yes — but only press the test button while the sign is powered on. Do not unplug or rewire components while power is connected.
Do these instructions apply to double-sided signs?
Yes. Each side of a double-sided sign operates independently but shares a similar card and connection layout. The same troubleshooting steps apply.
Note for older signs: This article applies to all types of LED signs. If you are not using our XIGNZ modular design, follow the steps outlined above to access your sign and locate the components as described.