/
Screen Flickering / Ghosting (Display Fluctuation)

Screen Flickering / Ghosting (Display Fluctuation)

Possible Causes & Solutions

1. Faulty Screen

  • A defective screen can display symptoms of flickering or ghosting.

  • Action: Replace the screen to verify if issue resolves.

  • If replacing the screen does not resolve the issue, proceed to next cause.

2. Faulty CPU

  • A defective CPU can cause screen flickering or ghosting.

  • Action: Replace CPU to verify if issue resolves.

  • If replacing the CPU does not resolve the issue, proceed to next cause.

3. EMI Interference with Communication Cable

  • Cause: Electromagnetic interference (EMI) disrupts the communication between CPU and screen.

  • Requirements:

    • A shielded screened comms cable must be used between Screen and CPU.

    • Cable must be kept away from high-voltage sources (lights, power cables).

  • Actions:

    • Ensure screened comms cable is installed.

    • Check cable routing to avoid proximity to high-voltage cables.

    • Install ferrite chokes on both ends of:

      • The cable to the screen.

      • The cable from the Fan Coil Unit to the CPU.

4. Power Supply to CPU (From Fan Coil Unit)

  • Cause: Drawing CPU power from the Fan Coil Unit can introduce EMI, leading to flickering. Although many installations work fine this way, EMI can still be a cause.

  • Recommended Action:

    • Provide a separate dedicated power source for the CPU.

  • Temporary Mitigation:

    • Before arranging a new power source, install ferrite chokes as mentioned above.

5. External Environmental EMI Sources

  • Cause: EMI from external sources (e.g., police stations, telephone towers, neighbouring equipment) can affect screen performance.

  • Examples: Neighbouring high-powered electronic equipment, strong Wi-Fi signals.

  • Actions:

    • Attempt relocating the screen to a different area.

    • As a last resort, create EMI shielding by:

      • Installing the screen in a cupboard lined with aluminium foil (acts as a Faraday cage).

Important Notes

  • Majority of flickering issues with comms-cabled screens are caused by EMI interference.

  • Both CPU and screen replacements typically rule out hardware faults.

  • EMI from HVAC systems (motors, compressors, fans) can affect signal integrity, especially when CPU power is sourced from these units.

  • International EMI immunity guidelines are inconsistent, making on-site mitigation essential.

Summary of Actions

  1. Confirm screened comms cable is installed and routed correctly.

  2. Install ferrite chokes on communication cables.

  3. Provide dedicated power supply for the CPU.

  4. Identify and mitigate external EMI sources.

  5. If unresolved, consider EMI shielding solutions.