Atlona Help Center

KB01074 - No video when using HDBaseT extenders and Cisco/Scientific Atlanta cable boxes

SKUs: All Extenders

Summary: No video when using HDBaseT extenders and Cisco/Scientific Atlanta cable boxes—


This article clarifies an incompatibility with older Cisco or Scientific Atlanta manufactured cable boxes that give an HDCP incompatibility message when used with HDBaseT extenders.




Customers have reported seeing either a black screen, a message saying there is HDCP compliance issues or will see “HDCP snow.”

About Clock Stretching

Clock stretching is a feature of HDMI that provides a clock signal which helps synchronize transmitters and receivers so that data like HDCP keys can be transmitted over longer distances and through more complex electronics.


Incompatible Sources

Due to the fact that older Cisco/Scientific Atlanta cable boxes do not support clock stretching, these sources are incompatible with newer HDBaseT chipsets used by Atlona.


Known Incompatible Models

Scientific Atlanta/Cisco/ Time Warner/ Comcast: 

  • 4000
  • 4250HD
  • 4642
  • 4742
  • 8300HD
  • 8600
  • 8642
  • RNG-110
  • RNG-150
  • RNG-200
  • CHS
  • X1



  • Check with your cable provider if they can replace the Cisco/Scientific Atlanta cable box with a different manufacturer (such as Motorola or Samsung). Installing a different manufacturer’s cable box should resolve the issue without any further action.


  • An AVR could help correct the issue by reclocking the signal itself. Please try this and see if video can pass: Cisco-> AVR-> Atlona Extenders-> TV





Article ID: KB01074

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