Failure to connect a Mac to one or more monitors? The solution

  • Sudden cuts in the image, making it look good at times and at other times it goes black.
  • Image interference, with colored stripes partially or totally present.
  • Green bars which, as in the previous case, can appear on the entire screen or in just a part, either fixed or intermittently.
  • The screen is completely black and does not show any image.
  • Intermittent flashes. (Attention to this, because it can be very dangerous for people prone to epileptic seizures).
  • Looks good, but offers teaches the same as the Mac without actually serving as a second screen on which to have other content.

Pre-checks you must do

Before you start investigating bigger problems, it’s a good idea to know some basic tips to keep in mind with the vast majority of Mac failures, including problems connecting to external monitors.

  • Check the software version from your computer, as it is recommended that you always be on the latest version of macOS available to ensure proper operation. If you go to System Preferences> Software update, you can find, if there is one, the new version ready for download and installation (if your version of macOS does not have that settings panel, go to the App Store> Updates).
  • Check the power connection, both from the Mac in case it is a desktop, and from the external panel itself. In the end it is something fundamental that, due to a mistake, we can forget and be the origin of everything. It is also convenient that if you use a MacBook, although it is not mandatory, you keep it connected to the charger.
  • Restart the Mac to thus eliminate all those problems generated by open processes, although it is recommended that you directly turn it off and turn it on again after a few minutes.
  • Remove and replace the cable that connects the computer with the external display. It sounds stupid, but many times the connection is not detected the first time and trying again may be the simplest and most effective solution to solving the problem.

Compatibility of your Mac with other displays

Although all Macs have been compatible with monitors for several years, it is not always clear how many displays it can support and what is the way to connect them. For this reason, it is important to know the specifications of the Mac and how to configure this connection.

How to know how many it is compatible with

If you have doubts about the compatibility of your equipment with these external elements, you have a very simple way to check it. You just have to follow these steps:

  1. Open the Apple menu (top left of the menu bar).
  2. Go to About this Mac.
  3. Go to the ‘General’ tab and take note of the Mac model you have.

mac model

  1. Without leaving this panel, go now to the ‘Support’ tab.
  2. Click on ‘Details’.
  3. When the Apple website opens, click on Technical Specifications (under Resources).
  4. Locate your Mac model and click on it.
  5. In the section ‘Video support’ (or ‘Graphics’) you will put the compatibility of the computer with monitors.

Logically, you must take into account the limitations of the device. If, for example, it supports a maximum of one monitor in 4K and you are connecting two, you will have already detected the problem and therefore you can take it into account when using other screens.

View the configuration panel

If your Mac is compatible with the display (s) you have connected, you may not have configured them properly. Within System Preferences there is a section called Screens in which you can precisely review all the settings related to it.

In this panel, which is like the one you see in the previous image, you can configure different aspects such as the resolution of the image that comes out on the screen of the Mac itself and the monitor, the color profile, on which side you want the external screen to be, if you want the content of both to be duplicated … In short, it will allow you to manage everything regarding the connection as long as it has been established well.

external displays mac

Possible damage to monitor, cables and adapters

With incompatibility ruled out, the chances that it is the hardware that is failing are getting higher and higher. Of course, before you go to technical support or start looking for new monitors to buy, keep in mind that they could also have an easy solution, at your fingertips and free of charge.

Cable and adapter review

The key element of connection between the Mac and the monitor is the cable and, therefore, a slight problem with this can trigger that you cannot see anything on the screen or be choppy. The first thing you should do is a visual check with which to check that the cable is in good condition, that there are no breaks in it and that it is not in a very tight position, as this could be the cause of the problems.

Please note that some breakages of this item are imperceptible naked eye. For example, you can try to bend the cable at some points and if you notice that when doing so the connection to the monitor returns, it is because internally there is a cut cable and that it does not have a good connection.

thunderbolt hdmi cable

Regarding the adapter, you should know that it is always advisable to use the native ports of the Mac. Although it is evident that it is not always possible, either because it does not have adequate ports or because they are already in use for other accessories. Therefore, the hub or adapter You use must be of good quality and fully compatible with both the monitor and the Mac itself (you will have that information in its own user guide).

Of course, you should also check that this intermediary between the cable and the Mac is in good condition. As well as it is advisable that you disconnect and reconnect as we indicated at the beginning of this post. And it is that the good connection of this element with the computer and with the monitor is essential, because if it is not fitted correctly in the port, it can cause problems like the ones you are experiencing.

If you don’t just find out if these are broken, it is advisable that you try another cable and / or adapter. This way you can make sure if it was those elements that were failing or, if there are still problems, it could be due to another cause. If you do not have any more, it is advisable that you buy another that gives you the option of returning it, since otherwise it would be a useless expense in case it is not the problem element.

Check Mac ports and monitor

You will have already checked the cables and adapters, but these can be fully compatible, of the highest quality and yet not get a good user experience. And what could it be due to? Well, as the title of this section advanced, the ports of the Mac and the external screen are damaged.

If they have multiple ports in which you can connect the connection cable, it is advisable that you try another to verify if it is the one you are currently using that is causing problems. You can also try connecting other types of accessories in case you are using a Thunderbolt port. See for example a memory stick, a headset with a USB-C end, or an external storage disk.

macbook ports

Regarding the monitor, it is more complicated to have two equal connections, but you can try to connect it to another computer or tablet that supports compatibility with it and thus rule out that it is a problem with its port.

Yes, besides do you have another monitor, you can check that everything is fine, being also very useful to rule out errors. If you do not have any, we cannot here recommend buying another one as we did with the cables and adapters, since in the end they are much more expensive items and returns are not always accepted.

Troubleshooting other hardware issues

At this point, the problem you are having is almost certainly due to a factory fault or defect of one of the two devices. Maybe even with both of them, which would be too unlucky, though not entirely out of the question.

Be that as it may, it would be appropriate for you to contact Apple’s technical service first and make a face-to-face appointment to bring your Mac so that they can examine it in search of the origin of the problem. If they finally rule out that it has faults, it will be with the technical support of the monitor manufacturer that you should contact to request a review of it.

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