• Hi All,

    I would really appreciate some help if anyone has come up against this..

    A recurring nightmare is turning up for the show and hitting 'signal not found ' when connecting my mac pro to multiple projectors..

    I am using 3-4 projectors of the thunderbolt ports with 'Belkin' converts to HDMI cable

    Eventually the mac recognises them but only after repeated plugging in and out..maybe 10-20 times...(sometimes never!)

    Very frustrating, nerve racking and being an intermittent problem very hard to trace the cause...

    Is there a more reliable converter than the 'Belkin ' out there?..different HDMI cables ? Hybrid fibre optic?...or is the problem within the mac? or in some kind of correct connection sequence that I am not doing..?

    I have this problem with both my Panasonic and Canon projectors and with long and short HDMI cables....

    Really stuck! advice please...


  • Beta Platinum


    Hi Andrew ,

    The problem is likely a Mac Pro external display limitation. If you look at the Mac Pro (2013) external display specification from Apple. It indicates that only two passive (single link) digital display adaptors can be used at one time. And only 1 x in conjunction with the HDMI port because the HDMI port shares a bus with the two bottom thunderbolt ports on the machine. However, the specification suggests up to six active adaptors can be used simultaneously.

    There are a number of work arounds and these include using a Matrox Tripple Head 2Go. Using analogue VGA connectors. Using active dual link digital connectors. 

    As soon as I try to use 2 x passive digital display adaptors (minDP to DVI) from the Thunderbolt ports I can only get 1 + the HDMI output operating at the same time.

    The Apple Mac Pro external display specification suggests it is only possible to use 1 x passive digital adaptor when using the HDMI connection or 2 x passive digital adaptors through the thunderbolt 2 ports.

    I have tried what appears to be a dual link active HDMI connector (one that has a USB as well as HDMI) to run an external monitor and this cable works, however it still does not allow me to add two more passive DVI adaptors, I can still only get two of the three displays working with it. 

    I do not have any active miniDP or Thunderbolt adaptors except for 2 x Matrox Tripple Head 2Go DP edition and these work well once the resolutions have been set-up for them. I can use them both simultaneously through two Thunderbolt ports. I can also continue to add displays using the remaining 4 thunderbolt ports - except for the limitation issue with passive digital adaptors - which is a pain.

    I am currently testing a set up with a MacPro that has ten displays connected. 2 x Tripple Head 2Go + 2 x VGA adaptors + 1 x DVI connector + 1 x HDMI as part of beta testing new software.

    This has been my recent experience with external displays on the MacPro (late 2013 trashcan).

    Best wishes



  • Izzy Guru


    If you are using a trashcan Mac you are limited to 2 or 3 HDMI outputs. If you are working with a MacBook Pro you can use all of you thunderbolt connections. If you want to use more than those on a trashcan you need active adapters like for example these: https://www.startech.com/suppo...

    Best Michel

  • @bonemap

    Hi, thanks very much for that - I must read spec!

    Very useful, many thanks Andrew

  • @michel

    Hi, thanks, I will look into these, thanks again Andrew

  • Beta Gold

    I am running a Trashcan with 6 HDMI outputs. In my case it worked only with the  MDP2HDSW from StarTech. Belkins not and even not Apple ones. SwitchResX helped me a lot to get everything tidy with different monitors.