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Just plugged in two LG 5K Ultrafine displays on either side of my iMac Pro 8 core. Everything on each display is slightly blurry. When I unplug one of the displays, the other returns to razor sharp clarity as I expect.

Each monitor is plugged directly into the iMac - no daisy chaining.

How can I get both monitors to show clearly?

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    If it's anything like the Mac Pro, you have to connect to a different Thunderbolt bus. Try using different TB ports - maybe at opposite ends of the bus.
    – Allan
    Jan 4, 2018 at 2:00
  • @nitrox1453, good to see that it worked for you - you should accept Allan's answer.
    – JW8
    Jan 4, 2018 at 6:06

2 Answers 2

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Most likely, you are plugging the displays into the same Thunderbolt controller (ports adjacent to each other). To ensure you're using the other controller, use the ports on the "opposite side" of the bus

According to Apple:

Note: The Thunderbolt 3 ports on your iMac Pro are managed by two controllers, one for the two left ports, the other for the two right ports. Each controller can support two 4K displays or one 5K display. So you can connect up to four 4K displays or two 5K displays to your iMac Pro. To connect two 5K external displays, for example, connect the first 5K display to either of the first two Thunderbolt 3 ports, and the second 5K display to either of the last two Thunderbolt 3 ports.


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The 8 core model simultaneously supports up to two (5K) external displays at 5120 x 2880 pixels running at 60 Hz, and can do this while the internal display is also functioning, so there's no doubt your Mac is capable of doing what you want.

Assuming your settings fit in with the above and you've already plugged them into the ports as described in Allan's answer, I would try doing an NVRAM reset and, if that doesn't work, a SMC reset as well.

How to reset NVRAM on the iMac Pro

Follow these steps:

  1. Fully shut down your iMac Pro
  2. Switch on your iMac Pro
  3. Immediately press and hold the OptionCommandPR keys.
  4. Keep the keys down until after the Apple logo appears and disappears for the second time.

NOTE: Upon reboot you may need to reconfigure some of your System Preferences (e.g. sound volume, display resolution, startup disk selection, time zone, etc).

How to reset the SMC on the iMac Pro

Follow these steps:

  1. Fully shut down your iMac Pro
  2. Press and hold your iMac Pro's power button for 8 seconds
  3. Release the power button and wait 5 seconds
  4. Switch on your iMac Pro

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