Atlona Help Center

KB01064 - No video output when connecting Atlona HDBaseT products with some older models of Scientific Atlanta (Cisco) cable boxes

Date issued: 04/03/13


Scenario: If you are using a Cisco or Scientific Atlanta manufactured cable box with a set of HDBaseT extenders from Atlona, and you are unable to get the video to pass or get a message stating there is HDCP incompatibility. 


Other HDMI sources (non-Cisco/Scientific Atlanta sources) work fine in passing video through the extenders

Explanation of issue:

Atlona’s understanding of the issue is: Cisco, who also owns Scientific Atlanta had manufactured cable boxes for various cable companies which used HDMI chipsets that do not have clock-stretching information built into them. Clock stretching is a feature of HDMI that provides a clock signal which helps synchronize video information that’s being transmitted. While the lack of clock stretching information was not a problem when using sources on older HDMI extenders, as HDMI extender technology improved as did its requirements which is why HDBaseT requires clock stretching information for signal transmission. Due to the fact that Cisco/Scientific Atlanta cable boxes do not send out clock stretching information, it causes the HDBaseT chipset used by Atlona to prevent the signal from passing. Unfortunately, there is no way to replace the HDMI chip used in the Cisco/Scientific Atlanta cable boxes. Adding a device to the system that can reclock the signal should help resolve this issue.

Please note, while Atlona keeps a list of cable boxes that have been known to have issues, this list is from 2014-15 and thus it’s difficult to keep a master list of ALL Cisco/Scientific Atlanta cable box models as they range by cable provider and market. As such, if you notice you have issues with getting video to pass from a Cisco/Scientific Atlanta cable box but other sources are working, it’s highly likely you have the clock stretching issue. Customers have reported seeing either a black screen, a message saying there is HDCP compliance issues or will see “HDCP snow”:

 (an example of “HDCP snow”)


Known models with issues: 

Scientific Atlanta/Cisco/ Time Warner/ Comcast: 

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


  1. 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.
  2. If you cannot get a different cable box but were planning on using the Cisco/Scientific Atlanta as an input source for an Audio Video Receiver (AVR) and the output of the AVR will go into HDBaseT extenders, the 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
  3. If you cannot replace the cable box and were not using an AVR, Atlona manufacturers two devices which can be used to reclock signal simply by installing them into the signal patch: The AT-UHD-SYNC and the AT-HDDA-2 are both devices that will take in a signal from the cable box and output a reclocked signal which can then be sent into the HDBaseT extenders where signal will pass. AT-UHD-SYNC and AT-HDDA-2 can be installed like so: Cisco-> AT-UHD-SYNC/AT-HDDA-2->Atlona Extenders-> TV/Projector

 Note, if using a HDDA-2 as a solution, you do not need to use both HDMI outputs but can do so if needed.


Article ID: KB01064

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