MBA 1,1-6,2 How can I get get my 2014 Macbook Air to output video to a USB-C cable?

[Amethyst1]

I'm.... really stumped at this point? What could cause this?

That… sucks.

You have the included miniDisplayPort and USB-A cables (necessary for supplying power) from the MacBook Air going to the Wacom Link Plus and plugged the projector into its USB-C display output, right?

The Wacom Link Plus also has a USB-C power input for supplying power to e.g. portable displays. Don’t plug the projector in there

 

[Wowfunhappy]

You have the included miniDisplayPort and USB-A cables (necessary for supplying power) from the MacBook Air going to the Wacom Link Plus and plugged the projector into its USB-C display output, right?

Yes, I plugged the USB-C cable going into the projector into the port with a little rectangle next to it. I did try the other USB-C port as well just for the heck of it—I tried every combination I could. Regardless, there were no signs of life.

It is possible the Wacom Link Plus I got is broken, I'm not exactly confident in the integrity of this eBay seller and I don't have a known-good USB-C display to test with. However, I doubt that's the problem. When I plugged my laptop into the Link's input USB-C port or its microUSB port, my laptop detected that it was connected to a USB 3 device (it appeared as a "TBT3-UDV Docking Station" in System Monitor).

---

The very good news is that I probably have a simpler solution. I said in the first post that:

Behind the scenes, the projector appears to be using HDMI input, so somewhere in the walls the USB-C signal is getting converted to HDMI, but I have no ability to mess with this.

It seems I never examined the podium closely enough—being in the classroom on a Saturday, by myself and with no time pressure, made it easier to notice things. There is a compartment under the podium with a Thunderbolt 3 Dock (I'm pretty sure it's this, it says tbt-udv on it). A USB-C cable goes into the Dock and an HDMI cable comes out. I didn't have my standard mDP-to-HDMI cable with me today, but I should be able to bring that on Monday and replug some things...

It still would be easier if I could use the standard USB-C cable, and I'm confused as to why I can't, but at least I have a path forward which doesn't involve using the school's crappy laptop forever.

 

[Amethyst1]

There's an easily-accessible compartment under the podium where you can see a Thunderbolt 3 Dock ([this thing](https://plugable.com/products/tbt3-udv) […]

And that might just explain it all.

TB docks require TB video input (encapsulating DisplayPort), not USB-C DP Alt Mode.

Some TB3 docks do work with that but it’s down to the controller (it needs to be Titan Ridge). The TBT3-UDV’s page goes back to 2017, suggesting it uses an Alpine Ridge controller which doesn’t accept USB-C DP Alt Mode.

So, you’ll need a Thunderbolt 1/2 cable and Apple‘s bidirectional Thunderbolt1/2-to-Thunderbolt3 adapter to (hopefully) get it sorted. More expenses

 

[f54da]

>TB docks require TB video input
Woah can you elaborate more on this? I never realized that there could be this additional layer of complexity. Indeed it seems "DP traffic as part of thunderbolt link" is a completely separate thing from "DP alt-mode" as described in https://www.thunderbolttechnology.net/sites/default/files/Thunderbolt3_TechBrief_FINAL.pdf

>The first device in the Thunderbolt link has a few options of how it can use this underlying PCI Express and DisplayPort traffic
>Consume the DisplayPort links by exposing them to a display panel, or a display connector(s)

The DP spec supported by thunderbolt DP-alt mode may also be different from usb-c alt mode as mentioned in

https://www.reddit.com/r/UsbCHardware/comments/qfitqa

Whose bright idea was it to create the most confusing connector in history.

Btw that bidirectional thunderbolt 1/2 to 3 adapter requires Sierra which I assume OP is trying to avoid since he wants to use 10.9.

 

[Wowfunhappy]

Btw that bidirectional thunderbolt 1/2 to 3 adapter requires Sierra which I assume OP is trying to avoid since he wants to use 10.9.

Yeah, that's not going to work unfortunately.

Is there any way to get a "dumb" box that takes in a (mini-)DisplayPort signal and converts it to whatever this "thunderbolt video" protocol is, without any involvement from actual source computer or operating system?

 

[Amethyst1]

Woah can you elaborate more on this? [...]

Thunderbolt has always supported encapsulating up to two DisplayPort streams in the TB stream, which requires a TB controller in the device (e.g. dock or display) to extract these DP streams and send them to a display or other sink. See here for my little experiments with that.

In addition to that, TB controllers can also do straight DP passthrough which enables a DP display (or adapter to e.g. DVI or HDMI) to be plugged into a TB port.

The DP spec supported by thunderbolt DP-alt mode may also be different from usb-c alt mode as mentioned in

One difference is that when DP is encapsulated over TB, the stuffing symbols aren't transmitted over TB but recreated by the receiving TB controller, allowing more "net" bandwidth (for higher resolutions/refresh rates).

The Pro Display XDR makes use of this in tiled mode: its two 3008×3384@60Hz tiles combined would normally require more bandwidth than TB3 provides, but as stuffing symbols aren't transmitted, it just about works out.

Btw that bidirectional thunderbolt 1/2 to 3 adapter requires Sierra which I assume OP is trying to avoid since he wants to use 10.9.

Yeah, that's not going to work unfortunately.

Good point. I don't have any TB3 devices the adapter would be useful with so I have no idea if it actually requires Sierra or a later version to work, or if it'll just do its thing even when the OS doesn't support TB3.

@joevt: Since you have a TB1 Mac and the adapter: have you tested if a TB3 device/dock works (video output would be sufficient) if running macOS older than Sierra?

Is there any way to get a "dumb" box that takes in a (mini-)DisplayPort signal and converts it to whatever this "thunderbolt video" protocol is, without any involvement from actual source computer or operating system?

The only "dumb" solution I'm aware of is a TB3 add-in card, such as this:

You'd need a riser or enclosure to put the card in and a way to supply it with power.

The theory is that you'd pipe miniDP from your MacBook Air to the card, which would be functional enough in this "zombie" state to convert that to TB3-encapsulating-DP, and the TB3 dock would accept that input... just to have its TB controller extract the DP stream that then goes into the dock's DP-to-HDMI converter and to the projector.

BTW, sorry for having sent you down the Wacom Link Plus route. I just assumed we‘re dealing with plain USB-C here

 

[Wowfunhappy]

BTW, sorry for having sent you down the Wacom Link Plus route. I just assumed we‘re dealing with plain USB-C here

No problem, you didn't know and I knew it was a gamble.

The only "dumb" solution I'm aware of is a TB3 add-in card, such as this:

My initial reaction was "oh, that won't work, I'm not going to carry a mini-PC around the school."

But you're saying it doesn't need to actually be plugged into a PC, right? But it does need power. I don't suppose the power could come from the USB-C cable?

I think this could maybe work if I can find a really small enclosure for it. Otherwise I'll just have to unplug the dock under the podium. (The problem with unplugging the dock is I have to always remember to put it back at the end of class. I cannot allow my weird technology choices to create problems for another teacher!)

 

[joevt]

@joevt: Since you have a TB1 Mac and the adapter: have you tested if a TB3 device/dock works (video output would be sufficient) if running macOS older than Sierra?

I can give it a try.

I think this could maybe work if I can find a really small enclosure for it. Otherwise I'll just have to unplug the dock under the podium. (The problem with unplugging the dock is I have to always remember to put it back at the end of class. I cannot allow my weird technology choices to create problems for another teacher!)

Try reading this thread:
https://hardforum.com/threads/use-usb-c-monitor-without-usb-c.1911817/post-1043180044
Don't remember if it worked for DisplayPort to Thunderbolt conversion.

 

[joevt]

@joevt: Since you have a TB1 Mac and the adapter: have you tested if a TB3 device/dock works (video output would be sufficient) if running macOS older than Sierra?

I installed Mavericks (had to change the date in the installer) and updated to 10.9.5.
The Thunderbolt 3 device was not detected when I connected it. Disconnecting the Thunderbolt 3 device causes a kernel panic. I think computer Sleep may also cause a kernel panic.
I tried booting Mavericks with the Thunderbolt 3 device connected. System Information.app says a device is connected but does not identify the device. A display connected to the Thunderbolt 3 device would not connect. It works in later macOS versions such as Sequoia.

I think the simplest option for this setup is to disconnect the display output from the Thunderbolt 3 dock and connect it directly to the laptop.

 

[Wowfunhappy]

Thank you so much for testing that for me! It's interesting that it kernel panicked—ironically, that would seem to indicate something is actually happening with the device, as opposed to nothing at all which is what I would have expected.

It might be interesting to see the panic log if you have it (especially if you could boot with keepsyms=1 enabled), but mostly for academic purposes. Yeah, it sounds like I'm stuck disconnecting the Dock.

 

[joevt]

Thank you so much for testing that for me! It's interesting that it kernel panicked—ironically, that would seem to indicate something is actually happening with the device, as opposed to nothing at all which is what I would have expected.

It might be interesting to see the panic log if you have it (especially if you could boot with keepsyms=1 enabled), but mostly for academic purposes. Yeah, it sounds like I'm stuck disconnecting the Dock.

It was basically Thunderbolt kext related symbols. Can't find the panic log.

 

[Amethyst1]

The Thunderbolt 3 device was not detected when I connected it.

Was it Alpine or Titan Ridge, just out of interest?

 

[joevt]

Was it Alpine or Titan Ridge, just out of interest?

Alpine Ridge. Echo Express III-D (Thunderbolt 3 Edition).

 

[Amethyst1]

Some small updates. I suppose you’ve resorted to moving the HDMI cable between the dock and your MBA, @Wowfunhappy?

[…] I have no idea if it actually requires Sierra or a later version to work […]

The answer is out there: AKiTiO says the adapter works in El Capitan, but not Yosemite.

But you're saying it doesn't need to actually be plugged into a PC, right? But it does need power. I don't suppose the power could come from the USB-C cable?

I don’t think so since the USB-C/TB3 port is strictly an output. Power has to come from the PCIe slot.

I think this could maybe work if I can find a really small enclosure for it.

This one is designed to fit in a 5.25in drive bay. I think this is as small as it gets.

 

[joevt]

This one is designed to fit in a 5.25in drive bay. I think this is as small as it gets.

Same size as the one I linked.