I am experiencing an issue with my MacBook Air M1 (2020, Sonoma 14.3) and Dell monitor (model P3221D), which supports USB-C. Until recently, I used the Dell monitor as my primary display without any problems. The monitor was also powering the MacBook through its USB-C connection. It worked out fine for more than 6 months.

However, suddenly, the MacBook stopped mirroring its display to the Dell monitor. The MacBook itself is functioning normally, and it still indicates that it is charging when connected to the monitor.

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Despite this, the image from the MacBook is no longer appearing on the Dell monitor. Additionally, while the MacBook acknowledges it's being charged through the monitor, it doesn't recognize the monitor in the display settings as an external screen.

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The Dell monitor displays a message stating that the USB-C connection is not identified:

"No USB-c signal from your device".

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I have tried:

  1. reconnecting the cables,
  2. turning off the macbook air
  3. upgrading macbook air to the latest version, Sonoma 14.3
  4. and using different ports on the mac, the monitor only has 1 USB-c. Unfortunately, the issue persists.
  5. I also tried a different USB-c cable. But, the same persists

Could anyone provide suggestions on how to diagnose and resolve this problem?


I tried again using a brand new Usb-C cable (see here) and an old Dell laptop running linux (NixOS). The monitor did not work.

  • 1
    Make sure you're using a cable which supports data connections. A power-only cable won't pass video.
    – IconDaemon
    Commented Feb 1 at 18:15
  • 1
    Apple's cable is only for charging, as you indicated.
    – IconDaemon
    Commented Feb 1 at 18:53
  • 1
    The first cable (or the connectors inside the plugs) the could certainly be damaged for data yet still pass power. Your best bet is to purchase a new USBC data cable and see if that works.
    – IconDaemon
    Commented Feb 1 at 19:39
  • 2
    480 Mbps indicates it's a USB 2 sped cable, which won't work for this since it's charging only. It doesn't have to be an Apple cable. I'd recommend something like this
    – JMY1000
    Commented Feb 1 at 23:07
  • 1
    I think that was a wrong choice. I believe that cable you want would be passive. You bought an active cable. I say this because the image shows a chip in it. Commented Feb 2 at 1:17

1 Answer 1


I've seen displays go bad before, one of which was a Dell display and it failed in a manner similar to what you describe. Hardware fails and it might just need replacement. It looks like you've determined the cables are good, the computer is okay, but did you test that the display is still fully functional?

To narrow down where the failure lies you'd need to test each part against known working parts. Double check that the computer can output video fine by connecting a different display. As an example, do you have an HDMI adapter and a TV somewhere to try? That can test if the computer is outputting any video.

Check that the display is fine by connecting to a different video source. If there's more than one video input and you have nothing else with USB-C output then perhaps test with some other video source that you have around. Do you have a DVD player? A tablet computer with video output? Try a cell phone with USB-C if you got one, that might have video output.

Given the description of the failure I suspect the display died. I've seen behavior like this before. Maybe only the USB-C input failed. I don't know if you have a "travel dock" like I do but it's got HDMI out and USB-C power in. Try something like that to connect power to the laptop and HDMI video to the display. It can at least buy some time until you can find a new display. If the display has a failed USB-C port that won't accept video then expect more to break in the display soon.

If the display is only 6 months old then there may be some kind of warranty. If so then contact Dell and make this display their problem to fix.

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