Issue connecting two Apple Thunderbolt Display 27" to MacBook Air M1 via DisplayLink dock

I see that you are trying to connect two 27" Apple Thunderbolt Displays – model A1407 – displays with 2560x1440 resolution and USB 2.0 and FireWire 800 hub ports – to a M1 MacBook Air.

As far as I know, there is no way to get this to work, with or without third-party DisplayLink workaround technology.

The Thunderbolt Display requires Thunderbolt input – so assuming that you have identified your displays correctly, and are not dealing with 27" LED Cinema Displays (model A1316), you made the correct choice in getting the Apple Thunderbolt 3-to-2 adapter.

If you had a Mac that supported multiple Thunderbolt displays, then you'd be in business. Examples of such Macs would be 14" MacBook Pros with M1 Pro and M1 Max chips . If you had such a Mac, you could connect up video as:

• 14" M1 Pro MBP port 1 --- TB3-to-2-adapter 1 --- Thunderbolt Display 1
• 14" M1 Pro MBP port 2 --- TB3-to-2-adapter 1 --- Thunderbolt Display 2

or

• 14" M1 Pro MBP port 1 --- TB3-to-2-adapter 1 --- Thunderbolt Display 1 --- Thunderbolt Display 2

This will not work for you. Your M1 MacBook Pro supports one external display with up to 6K resolution at 60Hz. One, not two.

MacBook Pro (13-inch, M1, 2020) - Technical Specifications - Apple Support

The fact that you are using a DisplayLink-equipped hub suggests that you know that your Mac does not support two external displays. This leads us to our next problem.

While there are third-party workaround products based on DisplayLink and similar technologies that you can use to attach extra DisplayPort and HDMI displays in a second-class way, there, are as far as I know, no such gadgets that output Thunderbolt signals or can be made to output Thunderbolt signals.

Your computer is not seeing your monitors because there is no Thunderbolt connection to your monitors.

ambroise81 wrote:

I had planned to buy a Mac Mini M2 Pro in the next few months but I think I'll bring that purchase forward.

According to the specs I've seen on Apple's website, it will be able to connect both monitors, right?

Mac mini (2023) - Technical Specifications - Apple Support

If I'm reading the Technical Specifications correctly, a Mac mini with the M2 Pro chip would let you connect both 27" Apple Thunderbolt Displays. That Mini supports a maximum of two USB-C or Thunderbolt displays, but even so, you would still be able to attach a third display ("one display with up to 4K resolution at 60 Hz") provided that you attached it via HDMI. The M2 Pro version of the Mac mini has four Thunderbolt 4 ports versus the two found on the M2 version. That means that even if you wind up using two of those ports for the monitors, you'll still have two left for other types of expansion.

I would suggest verifying that both 27" Apple Thunderbolt Displays work properly, when connected one at a time to your M1 MacBook Pro using just an Apple TB3-to-2 adapter. (If it turns out that either has a defective "hydra" cable, you can often work around that by running a TB1/2 cable from the TB2 side of the adapter to the TB daisy-chaining port on the monitor. Other issues might not be so easy to fix.)

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"Apple M2 Pro chip

Simultaneously supports up to three displays:

• • Up to three displays: Two displays with up to 6K resolution at 60Hz over Thunderbolt and one display with up to 4K resolution at 60Hz over HDMI
  • Up to two displays: One display with up to 6K resolution at 60Hz over Thunderbolt and one display with up to 4K resolution at 144Hz over HDMI
  • One display with up to 8K resolution at 60Hz or 4K resolution at 240Hz over HDMI"

ambroise81 wrote:

I’m seeking help to connect two Apple Thunderbolt Display 27" monitors to my MacBook Air M1 (2020).

I'm well aware that Mac M1s natively support only one external display, but here I'm trying to implement the workaround that uses a dock with DisplayLink.

Can't be done with those displays or with any display that requires Thunderbolt input. No DisplayLink workaround gadget of which I am aware generates a Thunderbolt signal.

Hardware:1.

Two Apple Thunderbolt Display 27" (so Thunderbolt 2).

A DisplayLink dock1. (USB-C).

Thunderbolt 2 to Thunderbolt 3 (USB-C male) Apple adapters1. .

USB-C female to USB-C female adapters1. .

USB-C male to HDMI adapters1. .

Configuration:1.

Each monitor is connected to a Thunderbolt 2 to Thunderbolt 3 (USB-C male) adapter.

2. The USB-C male adapters are connected to USB-C female to USB-C female adapters.

3. These USB-C female adapters are connected to USB-C male to HDMI adapters.

4. The HDMI adapters are connected to the DisplayLink dock, which is connected to the MacBook Air M1 via USB-C.

5. All the cables and adapters I used are Thunderbolt compatible.

USB-C to HDMI adapters are meant for converting USB-C (DisplayPort) output from a computer to HDMI input for a monitor. You're using them backwards. It's not clear that such adapters would work at all when connected backwards – but even if they did, they would generate USB-C (DisplayPort) signals, not USB-C (Thunderbolt) ones.

So you're feeding "No signal" or a USB-C (DisplayPort) signal into the USB-C side of a TB3-to-2 adapter that only translates Thunderbolt protocol. Even if you are getting USB-C (DisplayPort) out of the HDMI adapters, the signal will be immediately dropped by the Thunderbolt 3-to-2 adapters. Those adapters will only translate Thunderbolt, and Thunderbolt-encapsulated signals. They won't unwrap a Thunderbolt signal and make their TB2 side pretend to be a plain mDP port, and I'm betting they won't accept a USB-C(DP) one instead of a USB-C(TB) one, either.

So the Thunderbolt 2 sides of the adapters are producing "No signal" and the lack of a picture on the Thunderbolt Displays reflects that. And there's also no communication that would let the computer know that the Thunderbolt Displays were attached.

You matched the physical connectors but not the required signals.

You can get the correct signals with (M1 MBP --- TB3-to-2 adapter --- Thunderbolt Display) and none of the other stuff to break the Thunderbolt path. But you will only be able to connect one display.

Issue:1.

No monitors are detected by the MacBook Air, even when only one monitor is connected via HDMI to the dock.

2. If I only try to connect one of the Thunderbolt 3 adapter into a USB-C port of the dock I receive a notification: “Thunderbolt accessory not supported. Connect an accessory to a Thunderbolt port on this Mac.”

Expected result. See above.

Questions:1.

Has anyone successfully managed to use Thunderbolt 2 displays via a DisplayLink dock on a MacBook Air M1?

2. Is there a better solution to connect my Thunderbolt 2 monitors to my MacBook Air M1? (Daisy chain? But I've tried and nothing happens.)

3. I didn't notice when I ordered it but it is written nowhere in the specs of my dock that it is Thunderbolt compatible, so it may not be?

In a product description, the words "Thunderbolt compatible" often means that "This is a non-Thunderbolt product designed to work with 'plain' USB-C, but we're afraid that if we said that, Mac users would incorrectly think that it's incompatible with their systems. So we're using the 'Thunderbolt-compatible' term."

Thunderbolt 3 and 4 live on the USB-C connector. So by definition, all Thunderbolt 3 and ports are USB-C ports.

There are other protocols that run on USB-C connectors, and Thunderbolt 3 and 4 are optional, higher-end ones. So just because something is a USB-C port or device does not mean that it is a Thunderbolt 3 or 4 port or device. Most "Thunderbolt compatible" third-party products actually rely on DisplayPort, USB, and/or USB Power Delivery and have no support for connecting via Thunderbolt.