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I recently purchased an LG UltraFine display. On the back it has a USB-C (Thunderbolt 3) port to connect to the computer (no other ports - there are some downstream USB-C ports but that's it). When I connect the display to my recent MacBook Pro, it works fine.

However, I also have an older iMac (27-inch, Late 2014) that I'd like to try to connect it to... if I can hook it up somehow! The 2014 iMac has some USB-A ports on its rear, as well as Thunderbolt 2/MiniDisplayPort. Some googling suggests the Thunderbolt 2 port won't work, as no adapters exist. So, it feels like my best option, if it's possible, is to connect the USB-C monitor to the iMac via USB-A.

Can this be made to work? If so, what do I need to connect it? I'm not worried about getting full resolution or anything, just using it as an external monitor with the iMac at all.

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  • See this answer for information about converting TB3 to TB2. It covers the DisplayPort signals that you need to send to your new monitor
    – Allan
    Dec 5, 2022 at 4:39
  • Allan: That's the wrong adapter. The product listing specifically says: "Thunderbolt 3 to Thunderbolt 2 adapter is not reversible and will not connect TB3 peripherals to older computers with TB1 or TB2 ports". Which is my circumstance.
    – SoItBegins
    Dec 5, 2022 at 9:36
  • The trick here would be isolate the DP (video) signal which is what the adapter and active cable actually do. No, you can’t go from a newer TB peripheral to an older TB host, but the video signals are still the same. The USB-C connector on the back of the LG is just the connector it doesn’t mean that the display is a USB device. Check you device tree to confirm.
    – Allan
    Dec 5, 2022 at 22:04

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I googled and found the following Apple website.

Use the LG UltraFine 5K Display with your Mac or iPad

This website does state (though a link) that this monitor will work with your 2014 iMac, but will require the use of Apple's Thunderbolt 3 to Thunderbolt 2 adapter. Note: According to everymac.com, 2014 iMacs with Thunderbolt 2 have 27 inch internal displays and can support an external monitor with 3840x2160 resolution via Thunderbolt 2. In other words, this 5K monitor will only do 4K when used with your 2014 iMac.

Note: There are a slight discrepancies between the monitor model numbers found in the documentation used to create this answer. These discrepancies are given in the table below.

Source Model
LG Website 27MD5KLB-B
LG Owner's Manual 27MD5KL and 27MD5KLB
Apple Website 27MD5KL-B
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  • This is the monitor: lg.com/ca_en/monitors/lg-27md5klb-b.
    – SoItBegins
    Dec 5, 2022 at 9:41
  • @SoltBegins Your 2014 iMac does not support a 5K display.
    – Gilby
    Dec 5, 2022 at 9:51
  • @Gilby: The OP did state "I'm not worried about getting full resolution". Dec 5, 2022 at 11:04

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