External monitor fails to turn on with MacBook Air

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External monitor fails to turn on with MacBook Air

I purchased a new M4 Macbook Air today (which is running on macOS Sequoia 15.6.1) and my external monitor could not work with my new macbook air. The external monitor I am using is Samsung's Essential monitor (LS27C310EACXXK 27" S31C). I have checked the connections between the monitor and the macbook and everything is in place. The monitor still works with the previous Macbook Pro I purchased some 6 years ago, as well as my Ipad air, which I connected through an HDMI to type C docking cable. However, when I was using the same setting, the external monitor could not be detected by my macbook air. I tried switching it off and on again but it wouldn't work. Would be grateful if anyone could help with this issue, Thanks a lot.

[Re-Titled by Moderator]

Original Title: external monitor fails to turn on

Posted on Aug 22, 2025 10:22 AM

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Answer 1

Tesserax

Level 10

157,302 points

Aug 22, 2025 11:31 AM in response to Thomas091

The key here is that the new M4 MacBook Air is a bit more particular about adapters and docks than your older Intel-based MacBook Pro or iPad. Even though your HDMI-to-USB-C docking cable worked fine with the older devices, macOS on Apple Silicon tends to require active, standards-compliant adapters for video output. A lot of inexpensive “USB-C to HDMI” cables don’t fully support DisplayPort Alt Mode (what your Mac actually uses to push video out), so the Mac just doesn’t see the monitor.

See if any of the following can help:

Go to System Settings > Displays and click the “Detect Displays” button while the monitor is plugged in. If nothing shows, that confirms it’s not being recognized at all.
Use a known good USB-C to HDMI adapter (ideally Apple’s USB-C Digital AV Multiport Adapter or a reputable brand like Anker/Belkin). A direct USB-C to HDMI cable can be hit-or-miss depending on chipsets inside.
The M4 Air supports external displays on both Thunderbolt 4 ports, but testing the other port rules out a physical issue.
Make sure the Samsung is explicitly set to the HDMI input, not left on auto-scan.
Test with another monitor/TV if possible.

Here are some adapters I suggest that you consider:

Apple USB-C Digital AV Multiport Adapter. Model: MJ1K2AM/A
Anker USB-C to HDMI Adapter (4K\@60Hz). Model: A8312
Belkin USB-C to HDMI Adapter (4K\@60Hz). Model: AVC005btBK

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