iMac won't detect my external monitor

Discussion in 'iMac' started by STC1709, Apr 30, 2014.

  1. STC1709 macrumors 6502

    May 27, 2009
    So I have a dell 21in which has a VGA cable. I bought an adaptor for the mac to connect into the mini display port. Plugged it in, went to system preferences and it wouldn't detect. When the dell monitor is turned on it looks for input then it goes into power save mode (probably bc it cant connect).

    I tried resetting the PRAM, nothing. Tried restarting, plugging and unplugging cables, nothing. I have a late 2009 24in iMac. I'm beginning to believe that it might be the adaptor itself, but I've been reading that this is sort of a common problem with macs.

    Anyone have any suggestions on how to get this to work?

    Thanks in advance.
  2. aggri1, Apr 30, 2014
    Last edited: Apr 30, 2014

    aggri1 macrumors 6502

    Jul 21, 2010
    This sounds familiar, but a quick search failed to find the post I had in mind.

    Does the Dell monitor have another connection option? I think I can recall having issues with one type of connector with my 27" 2010 and some cheap second display, and I am currently using the Mini-DisplayPort (MDP) to DVI connector so I guess that the MDP to VGA one (the only other MDP converter I have) was the one which I couldn't get to work...

    Sorry can't be of more help.
  3. STC1709 thread starter macrumors 6502

    May 27, 2009
    It has a DVI port too, hmm wonder if i use that if itll work. I'd hate to have to buy a dvi cable and the adaptor to end up finding out that it doesnt work then I'm stuck with 2 useless parts.
  4. mmomega macrumors demi-god


    Dec 30, 2009
    DFW, TX
    Keep the receipt. Return the one that doesn't work.
  5. robgendreau macrumors 68040

    Jul 13, 2008
    Aargh. It's a black art. Generally, though VGA is the dumbest connection. Macs especially seek out a smarter connection, i.e. a digital one like DVI (and there are flavors of that, DVI-I and DVI-D). That way the monitor and computer communicate to set the resolution and such. VGA is analog-stupid; you generally need something to convert a recent's computer's video out to analog to get that to work. So when you see an Apple Mini Display Port > VGA it's an adapter, not just a cable. And note it's directional. But even when you get that going you may need to manually set the resolution, using the Displays control panel or something like SwitchRes X. Your monitor in VGA isn't sending any info back to the mac about that I expect. That's one reason why DVI is preferred (the other is that it gives a better picture).

    If you have DVI on the monitor, that's generally more reliable and easier to use. Your Mac should support it. Monoprice sells Mini Display Port to DVI cables for about $10 for 6'.

    But having said that, VGA should work. Would probably help if we had the specs to the monitor. Have you tried setting it's native resolution and frequency in Displays? The 2009 iMac might not support resolutions higher than 1920x1200, or really high refresh rates.
  6. STC1709 thread starter macrumors 6502

    May 27, 2009
    Hmm very good info that I did not know about, thank you. I might be better off just buying a DVI cable to plug into the monitor then buying the DVI adaptor to hook it to the mac (I only have a VGA cable bc thats what the monitor came with so i'd have to buy a DVI one)

    unfortunately I can't find the model number of the monitor haha. Nothing listed anywhere on it.
  7. STC1709 thread starter macrumors 6502

    May 27, 2009
    I might give this one a shot here…

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