Why the Apple LED Cinema Display doesn’t work with a Thunderbolt 3 adapter

Glenn Fleishman
11 May, 2017
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Ross Mclauchlan writes in with a display problem:

I recently purchased a MacBook Pro and have an Apple LED Cinema Display, and am perplexed that I can’t get the display to work.

Ross is using an Apple Thunderbolt 2 to 3 adapter, but the trouble is the Apple LED Cinema Display models don’t use Thunderbolt 2. We’ve written about this before but it’s not obvious, even when you’re paying close attention.

mac911 mdp tb symbols

The LED Cinema Display series relies on DisplayPort for both the physical connection and the logical one – the way in which video is encoded as data and sent across the physical wiring. The Mini-DisplayPort connector is identical to a Thunderbolt 2 in appearance, except for a tiny logo. The Mini-DisplayPort logo that appears on a cable jack and an adapter port looks like a monitor holding its hands up in surrender (a rectangle with a vertical line on either side). Thunderbolt 2 jacks and ports have a lightning bolt. (Ironically, Apple’s Lightning standard doesn’t use a lightning bolt.)

Plugging a Mini-DisplayPort monitor’s jack into a Thunderbolt 2 port on a Mac or at the end of a chain of Thunderbolt 2 devices was supported through clever backwards compatibility that fails with Thunderbolt 3, including a Thunderbolt 2 to 3 adapter. Instead, you need one of the adapters or docks I reviewed earlier this year. There are more options now and varied ones, so read product reviews carefully if you purchase one I didn’t test.

And just to be more confusing, the Mini-DisplayPort converters I reviewed don’t output Thunderbolt 3. Rather, they send DisplayPort video signals over USB-C in a way that Thunderbolt 3 allows for with backwards compatibility. Those adapters can thus be used with a 12-inch MacBook, which primarily supports USB 3 and DisplayPort over the USB-C connector, as well as with 2016 MacBook Pro models, which support Thunderbolt 3, USB 3, and a host of other standards over USB-C.

No, it’s not just you. It’s confusing to have a single connector style (USB-C or Mini-DisplayPort) with incompatible standards that work over it.

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