Trouble Getting iMac To Run Second Display

Discussion in 'Mac Accessories' started by nickyj182, Mar 10, 2016.

  1. nickyj182 macrumors regular

    nickyj182

    Joined:
    Feb 12, 2002
    Location:
    Morehead, KY
    #1
    I have the following iMac:

    Apple - 21.5" iMac® - Intel Core i5 (1.6GHz) - 8GB Memory - 1TB Hard Drive - Silver

    It's the latest entry level model currently. I'm wanting to run a second display, I have a decent second monitor that only has a VGA input. So I bought this cable:

    http://www.amazon.com/gp/product/B013G4EQ9C

    I put it in one of my Thunderbolt ports in the back of my iMac and the VGA end into the monitor. When I turn the monitor on it says Input Type Not Supported.

    The cable says its compatible with Thunderbolt, is there something simple I'm missing here? Isn't my iMac capable of running a second monitor?
     
  2. matreya macrumors 65816

    matreya

    Joined:
    Nov 14, 2009
    #2
  3. campyguy macrumors 68040

    Joined:
    Mar 21, 2014
    Location:
    Portland / Seattle
    #3
    OP, that cable is a passive adapter, a passthrough, if you will? - you'll need an active adapter which includes a signal converter from the DP signal generated by your iMac to the VGA signal required by your display. Lots of good ones available - Apple and Monoprice make good and not-expensive active adapters. Jump to:
    https://support.apple.com/en-us/HT204149#anchor10 for info about this...
     
  4. priitv8 macrumors 68030

    Joined:
    Jan 13, 2011
    Location:
    Estonia
    #4
    There is no such thing as Passive or passthru DP-to-VGA adapter. DP is 100% digital connection, VGA is 100% analog connection. So every such adapter contains at least 3 D/A converters (for R, G and B).
    The problem I experienced with such adapter (i also had relatively cheap one) was that it didn't handle hight refresh rates from Mac. Try to turn your 2nd monitor output down to 1920x1080 and 50 or 60Hz refresh rate. In OS X Displays Preferences.
     
  5. campyguy macrumors 68040

    Joined:
    Mar 21, 2014
    Location:
    Portland / Seattle
    #5
    I'm guessing you didn't read Apple's own documentation, which I linked to? Or my post? :rolleyes: Yes, there are passive adapters out there - they attach to eGPUs which we used to use in my office.

    Regardless, that wasn't my point at all here - the cable is acting as a signal passthrough (as it's not an active adapter) and an interface adapter, and an active adapter is what the OP needs.
     
  6. priitv8, Mar 11, 2016
    Last edited: Mar 11, 2016

    priitv8 macrumors 68030

    Joined:
    Jan 13, 2011
    Location:
    Estonia
    #6
    well I'm indeed lost on the active vs passive mDP-VGA adapter, but the $10 dongle OP bought is as active adapter as it can get. If Amazon's description is to believe, then it connects to MacBook on one end and directly to analog VGA monitor (up to 1080p) on the other. That's all he needs. Only question if that adapter is up to task with Mac's default output settings.

    Active vs passive discussion in Apple's article concerns digital-only interfaces (DP, DVI, HDMI) only.

     

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