External monitor with iMac 5k

Discussion in 'iMac' started by CaptainJack406, Feb 1, 2016.

  1. CaptainJack406 macrumors newbie

    Feb 1, 2016
    Hi all,

    I took delivery of a brand new Apple iMac 5k system and am having issues with running external displays on it.

    I have a Dell U2412M 24" monitor, which worked perfectly well with my old Hackintosh - very sharp and clear. However, upon connecting it to my iMac, I found that the screen is less than sharp, fonts are washed out and generally looks like I am looking at a 15 year old LCD screen.

    The resolution is set to "Default" (1920x1200) in Display settings and I've tried all sorts of fixes on the web, like forcing the Mac to output in RGB mode (it already was), changing font smoothing through Terminal (helped but only slightly) and nothing helped.

    Someone suggested using SwitchResX, which looked promising. I noticed that if I chose a HiDPI resolution of 1600x900, the display was much sharper, though still odd because it's not the monitor's native res. If I chose a non-HiDPI version of the same resolution, it became all blurry again.

    I thought I would be able to create a HiDPI resolution of 1920x1200 (which is, apparently, actually 3840x2400) but SRX is simply creating a display profile with 3840x2400 and not 1920x1200 HiDPI. I've tried a bunch of other programs but none seem to want to create the res I want. I even tried creating my own display profile with IOReg/Plist but that didn't seem to want to play ball either. All attempts to create a HiDPI version of 1920x1200 end up with non-HiDPI resolution of 3840x2400 :(

    I already have an Apple Cinema 24" on the way but I do need 3 monitors and would like to get this Dell going properly.

    The connection is TB to DVI using an el-cheapo cable from Amazon, though I can't imagine that a newer, more expensive cable would fix this. The monitor does have a DP port, but I don't see why that would be better (and Google suggests that it won't be better...).

    Any ideas?
  2. maflynn Moderator


    Staff Member

    May 3, 2009
    It could be the connection, from TB to DVI. FWIW, my 21" Apple ACD is crisp when I have it hooked up to my iMac.

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