Pavel Jelic Apple computers are among the most perfect work tools, as practically all of you can confirm. If you would like to increase your work efficiency even more, you can connect an external monitor to your Mac or MacBook, which allows you to enlarge your work area. In this way, you can easily open several windows next to each other and work with them easily, or you can make your work more pleasant by watching a video that you play on an external monitor. But from time to time problems can occur after connecting an external monitor - for example, artifacts start to appear, or the monitor disconnects and does not connect again. What to do in such a situation?
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Plug the adapter into another connector
If you are a newer Mac user, you most likely have a monitor connected via an adapter. Either you can use a single adapter directly on the connector reduction, or you can use a multi-purpose adapter that, in addition to the video input, also offers USB-C, classic USB, LAN, an SD card reader and more. The first and easiest thing you can do when the external monitor is not working is to connect the adapter to another connector. If the monitor recovers, you can try plugging it back into the original connector.
Perform monitor detection
If the above procedure did not help you, you can re-recognize the connected monitors - it's nothing complicated. First, in the upper left corner, click on icon , and then select an option from the menu System Preferences… This will bring up a window with all available sections for managing system preferences. Here now find and click on the Monito sectionrand make sure you are in the tab in the top menu Monitor. Then hold the key on the keyboard Option and in the lower right corner tap on Recognize monitors.
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Sleep mode or restart
Believe it or not, in many cases, a simple hibernation or reboot can help solve various problems. Unfortunately, users often ignore this very simple procedure, which is certainly a shame. To put your Mac to sleep, just tap on the top left icon , and then selected an option Narcotize. Now wait a few seconds and Mac afterwards reawaken. If the monitor did not recover, then reboot - click on icon , and then on Restart…
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Busy adapter
As mentioned above - if you own a newer Mac, you probably have an external monitor connected to it using some kind of adapter. If it is a multi-purpose adapter, believe that it may become overloaded during maximum use. Although it shouldn't happen, I can say from my own experience that it really can happen. If you connect absolutely everything you can to the adapter - i.e. external drives, SD card, LAN, then start charging the phone, connect the monitor and plug in the charging of the MacBook, then a huge amount of heat will start to be generated, which the adapter may not be able to dissipate. Instead of damaging the adapter itself or something worse, the adapter will simply "relieve" itself by disconnecting some accessory. So try to connect only the monitor itself via the adapter and gradually start connecting other peripherals.
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Hardware problem
If you have done all the above procedures and the external monitor still does not work as it should, then there is a high probability that the problem is in the hardware - there are several possibilities in this case. For example, the connector itself, which you use to connect the adapter, may have become detached, which you can find out, for example, by connecting another adapter, perhaps only with an external disk. Furthermore, the adapter itself could have been damaged, which seems like the most likely possibility. At the same time, you should try to replace the cable that connects the monitor to the adapter - it can be damaged over time and use. The last possibility is the fact that the monitor itself is not working. Here you can also try to replace the power adapter, or check whether it is correctly connected in the socket. If everything is fine from the side of the extension cable and the socket, then the monitor is most likely faulty.
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Flying around the world with Apple 
You didn't describe a few basic problems that I'm constantly dealing with, so I'll add them:
– USBC connectors are inherently unstable, they wear out when peripherals are frequently connected/disconnected, and then you just need to press the MacBook on the table and the connected external drive is there (and no, don't try to advise buying a new cable, there really isn't a problem)
– Apple has (unacknowledged, how else) problems with powering external adapters connected via the USBC connector (even with original Apple adapters, I sometimes get a message about the port being disabled, because the adapter (yes, only the adapter itself) requires too much current - then a complete shutdown is necessary – authorized service diagnosed macbook and peripherals as problem-free – apple care doesn’t know how to deal with it – evidently a design problem)
– There are really a lot of wires in the USBC connector and there are really a lot of different standards on them, and compatibility with the monitor is certainly not guaranteed just because the support for USBC is written on the monitor – I have tried several external monitors recently and the only one really works (full resolution, 100Hz , HDR) is the one that declares Thunderbolt 3 support
– Another problem is with the cable – it’s not USBC like USBC – I recommend investing in a certified cable for Thunderbolt 3 (if you want to power the MacBook through it, check that it has it in the specification and there are enough watts – for example for my MacBook Pro 16, a 100W cable is needed - I really can't push it through the thin one I have for the iPad)
– And finally – my practically new (few months old) MacBook Pro 16 2019 in almost full fire (140k) does not have enough power to comfortably operate one connected external 4k monitor (just connect via TB3 port/cable and the fans can go crazy – again apple care he doesn't know how to deal with it - I even did a clean installation of BigSur because of them, to exclude the influence of pre-installed SW)
Conclusion: I've liked Apple for decades, but it's really not what it used to be... If I didn't have such an inherent dislike for Widli, I probably wouldn't be with them anymore... So we'll see if the M1 will make the situation better or worse...
Well, I confess that I don't understand what people have about Apple. I bought it because the applications issued by the state administration do not support Linux. but it's really a big disappointment. almost nothing works as it should.
And I don't see the most fundamental problem I faced with my first MacBook anywhere - a quality cable with support for 60 Hz image transmission. Without it, the image went to my monitor, but the mouse movements were choppy, it kept cutting. I tried several combinations (HDMI didn't have the necessary sharpness, the DVI adapter did work, but no glory...), finally I read somewhere on the forum that you need to buy a really high-quality cable that has declared support for 60 Hz image transmission in high resolutions. Since then, no problem…
Hello, for some reason I can't connect the monitor. If I connect the HDMI, the Macbook becomes a secondary extended monitor and the main one (which is supposed to be secondary) doesn't even turn on and it's black. It says "no video input". If I connect the macbook to the TV in the same way, it does not cause any problem. I really don't know what to do with it. Thank you for answer.
Dobrý den.
I have exactly the same problem. The external monitor worked as a desktop extension without any problems for about a month. After turning it on once, it simply remained black and the only displayed information is "no video input". Changing the HDMI cable, using a T3 cable, rebooting, or any of the above methods does not work. Did you somehow manage to deal with the problem? I will be grateful for any response.