what to know
- Go to System Settings > Display > Hold down the Option key > click Detect Display .
- Go to System Settings > Display and check the Resolution and Brightness settings.
- Also, check the monitor cable connection and update the adapter software (if applicable).
This article provides tips on monitor settings and cable specifications to check and resolve external monitor not detected by Mac.
Try the following fixes in order to try to get your Mac to recognize the external monitor.
If you're using a MacBook, try plugging it into a power source. Some power saving settings limit certain processes to extend battery life.
Make sure your Mac supports more than one additional monitor. You can check the number of supported monitors by clicking the Apple icon System Settings > Help > Your MacBook > and looking under Monitor Support or Video Support .
On older versions of macOS, click the Apple icon > About This Mac > Support > Specifications > Graphics & Video Support .
Check your cables carefully. The first thing you should do is make sure your cables are correct and secure. Verify that all wires between your Mac and monitor are securely connected, and make sure the monitor is plugged in.
If the cables look fine, try unplugging them for a while and then plugging them back in. Restarting the external monitor may cause your Mac to retry recognizing it.
If you use an adapter, make sure your monitor and cable combination is compatible with your Mac. Some Macs use USB-C only or both Thunderbolt and USB-C connections, and some Thunderbolt versions require a Thunderbolt-specific adapter.
In the case of a docking station, check its manufacturer's support website and download new drivers (if applicable).
Go to System Settings > Display to check your resolution settings. Hold down the Option key. This combination will reveal a hidden "Detect Display" option in the lower right corner. Click this button so your Mac can scan for connected monitors.
On older macOS versions, this option can be accessed by selecting System Preferences > Display > Zoom .
Choose a different resolution. Still in the resolution settings, Ctrl-click the resolution in the list > and select Show Thumbnails . Choose a thumbnail other than the default option and see if you're prompted to change it.
You may see a radio button next to Scaled . If you do this, select a different resolution from this view.
Deselect automatic brightness adjustment. Under "Brightness ," uncheck the box next to it or deselect "Automatically adjust brightness" and use the switch to adjust brightness manually. This may resolve the issue if the brightness of the external monitor is too low to register.
Let your Mac sleep for a while, then wake it up to see if there are any changes to Display preferences.
Restart your Mac after connecting the external monitor.
Finally, disconnect all cables, turn off your Mac and external monitor for a minute or two, then reconnect the cables and turn everything back on. If your monitor still doesn't work, repeat the steps in Display Setup.
Avoid daisy-chaining multiple adapters and cables together to increase your chances of success. Macs tend to work well with external monitors when using direct Apple-branded or compatible cables and adapters.
Problems between your Mac and external monitors can occur for a variety of reasons, including:
- Incompatibility between Mac and monitor.
- Faulty cable (or wrong cable).
- The power saving options in MacBook prevent it from running an external monitor.
- Outdated dock driver or software.
- The settings in your Mac's display settings are incorrect, including brightness and resolution.
To expand your Mac's display, set up dual monitors on your Mac. Connect your monitor using HDMI, Mini DisplayPort, USB-C, or Thunderbolt ports. Place the monitor and power on your Mac. Open System Settings and select Extended Display from the Use as drop-down menu. Alternatively, select System Preferences > Display > Arrange and uncheck Mirror Display .
To set an external monitor as your primary monitor, open System Preferences or System Settings > Displays > Arrange or Arrange . There will be a white bar above one of the displays. Click and drag the bar to another monitor to set it as your primary monitor.
To prevent your Mac from going to sleep and turning off the display, go to Apple menu > System Settings > Lock Screen . Alternatively, select System Preferences > Energy Saver > and move the slider to Never . Your Mac's display won't turn off now.
