Check for faulty ports or cables. An average user can do this by connecting different combinations of devices and seeing if they work. Say, for example, you’ve found that connecting your MacBook to your TV doesn’t work. Then, try checking if the MacBook works with the monitor, or if the TV works with a different Mac or PC. In case there are multiple ports of the same type on your devices, try different ports. Try a different cable, too. If a HDMI cord not working Mac, the most you can do is discard and replace it. If a port malfunctions, you’ll probably need to take it to a repairman.
Check if you chose the right adapter. There are plenty of cases where you may be forced to use an adapter. For example, MacBook Air only has Thunderbolt ports. If that’s the case, make sure that the adapter supports video throughput, and try a different one if you suspect that it doesn’t.
Try detecting the displays in Settings. Go to the Apple menu, then System Preferences > Displays. Hold Option and press the Detect Displays button. Sometimes, a TV won’t work when you connect it, but it will work fine once you detect it manually. Reloading and re-plugging it may also help.
Disable HDMI Deep Color. For example, on LG TVs, it can be found under Settings > Pictures. It may sometimes cause the HDMI connection with Mac to fail. This is commonly suggested in TV instruction manuals as a troubleshooting step. By the way, try checking the manual for possible fixes, too.
Try to use Time Machine to roll back to an older update. Some macOS updates can introduce errors that will make your system incompatible with a TV. If that’s the case, do a rollback and use the older version until the bug is patched out.
If the sound isn’t coming through, do the following. Unplug any other audio devices, such as headphones. If you’re using an adapter, verify that it can transfer audio, and that your Mac can send audio through the port you’re using (find its specifications on the Apple website). Also, go to the sound settings and select the TV as an output device.
If the TV output is incorrectly sized, go to Displays. Play around with the resolution on your Mac – try to match the aspect ratio of the TV. Select “Scaled” to see more resolution options. The Underscan bar might also help.
Restart or, if all else fails, Factory Reset your MacBook. Restarting is the simplest step you can take. A Factory Reset should be your last resort, and if you decide to do it, don’t forget to back up your data, since it will be deleted in the process.
