Sonoma 14.3.1 - Thunderbolt Display 27 not working

Solved the problem by unplugging the display from the wall for some minutes. Maybe the problem does not lie in the update, because I plugged in my iPad M1 and there was no image either. After unplugging from the wall the MacBook and the iPad work.

Had exact same issue, 27" Thunderbolt display not working with M1 MacBook Pro (Sonoma 14.5).

I've now got things working again:

• Set preferences to ask when a device is connected every time to accept
• Used a cable from the other Thunderbolt port from the display - ignoring the hard-wired octopus cable

All seems good at the moment.

Could be an issue if you are using the built in (octopus) cable as they are known to go bad. Use a TB2 cable connected directly to one of the TB ports on the display bypassing the all in one cable.

Hi,

After I updated to Sonoma 14.6 the problem is fixet, hope it helps

Yep, still working just fine. It's been over 1 week now with no issues.

Whenever I connect OS X asks me if I want to allow USB device connection.

Then, for as long as it is connected with the cable, it always turns the external display on - even if my machine has been in Sleep for more than 24 hours.

So, I'd say solution that worked for me is fix settings in Preferences to always ask for connection confirmation and to use a TB2 cable from the spare TB port at the back of the Thunderbolt and not to use the Octopus cable.

As a sidenote - after I'd updated to Sonoma, my mag safe charger stopped being recognised as well as the Thunderbolt Display. Whether this was a coincidence or not. But I let the MacBook Pro completely deplete it\s battery so it was totally flat. Then, after charging using one of the USB ports, it finally came back to life and it recognised the charger again. I think some people replicate this with a keystroke combo during startup to reset the power module PCB (or something) - which seems to have fixed the problem for some users too.

I then adjusted the USB settings and used the different cable for the first time. It's been great ever since

You should be fine. Just never update once things are working or you might regret it!!!

Could be a coincidence. Try this: Unplug the display from the wall, wait 3 minutes and reconnect. This will reset the display settings.

Although I could solve the problem by unplugging the display from the wall, after some days the display randomly starts to have blackouts again. It just won’t wake up. Still the solution is to unplug it from the wall. Very annoying. So I think that the problem is indeed linked to the current macOS version.

Then I would try the cable. I suppose the adapter could be bad but I doubt that.

I suppose it could be the adapter although they seldom fail

Don't know where you are based, but just google "Apple Thunderbolt 2 cable" there's usually some from retailers and a bunch on eBay.

Did you find any solution? I have problem too. Connected monitor does is not detected at all. System information shows no device connected at all 3 Thunderbolt/USB4 ports. I was hoping to the external cable...

I will try to find the external cable and test. I just got the monitor, was first time to connect it on a MacBook M3. The octopus cable looks also a bit worn-out at the edge. I plugged a couple of USB devices at the back of the monitor and they are charging... I hope I will have some luck...

A__J_, I'm curious to know if your 27" Thunderbolt display is still working with your MacBook Pro in Sonoma using your tow-part solution around device connection settings and the display's Thunderbolt port.

I'm considering purchasing a used 27" Thunderbolt display.