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Difficulty: HardVideo, Display, and Projector Issues

A technician is installing a presentation system in a corporate conference room. The workstation is connected to a 4K commercial display located 50 feet (15 meters) away using a standard passive HDMI cable routed through wall conduits. During testing, the display intermittently cuts to a black screen for several seconds, shows digital noise ('sparkles') in dark areas of the image, and occasionally drops down to 1080p resolution automatically. Updating graphics drivers and adjusting operating system display settings fails to resolve the problem.

Which of the following is the MOST likely cause of these symptoms?

  1. Digital signal degradation caused by exceeding the maximum distance limit of a passive HDMI cableAnswer
  2. B
    Overheating Video RAM (VRAM) on the workstation's dedicated graphics card
  3. C
    A failing CCFL backlight inverter board inside the commercial display monitor
  4. D
    Inadequate refresh rate configuration caused by an unshielded DisplayPort-to-HDMI adapter

Answer

Digital signal degradation caused by exceeding the maximum distance limit of a passive HDMI cable
High-speed digital video formats like 4K HDMI require high frequency signal transmission. Standard passive HDMI cables experience severe attenuation (signal degradation) when extended beyond 15 to 25 feet. At 50 feet, the signal integrity degrades sufficiently to cause intermittent loss of display sync (black screens), digital noise ('sparkling' pixels), and automatic renegotiation to lower bandwidth resolutions such as 1080p. Using active HDMI cables, fiber-optic HDMI cables, or HDMI-over-Cat6 extenders solves this limitation.

Step-by-Step Solution

1
Analyze the symptoms reported in the scenario.
The system exhibits intermittent black screen dropouts, digital noise ('sparkles'), and automatic resolution downgrading to 1080p over a 50-foot run.
These symptoms specifically indicate loss of digital signal integrity (attenuation) and clock synchronization failures between the transmitter and receiver.
2
Evaluate the physical media and distance constraints.
Standard passive HDMI cables lose signal strength significantly past 15–25 feet, especially when trying to maintain high bitrates required for 4K video.
At 50 feet (15 meters), a passive HDMI cable cannot maintain the signal timing and voltage thresholds required for reliable 4K video transmission.
3
Identify the appropriate remediation technology.
Replacing the passive cable with an active HDMI cable, active optical cable (AOC), or an HDBaseT (HDMI over Ethernet) extender will restore full signal integrity.
Active solutions amplify or convert the signal (to optical or differential twisted-pair) to overcome attenuation over long distances.

Key Concept

Video Cable Distance Limits and Digital Signal Attenuation
Estimated Time:2m 0s
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Topics

Video, Display, and Projector Issues

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