MacBook won't detect external display

Sorry I should have been clearer. It actually works with High Sierra. I probably spent about a month now trying to find different solutions and only two things work for me. Buying this adaptor or rolling back to Sierra, but that depends if you have kept a a Time Machine backup to restore to. I have a Acer 27" G277HU which is running at 60Hz connected via HDMI. I can't comment on individual monitors though but know that after much frustration I finally have found something that seems to work now. To be honest I don't see why I actually had to spend anymore more money given that it appears to be a problem with the operating system. Truth be told I suspect Apple want people to splash out extra cash on their LG partnered monitors which connect directly via USB-C.

Just spoke with Apple enterprise support on this. He was very helpful! It is not a High Sierra issue, in my case I needed you upgrade the driver of my external device. I am using a diamond DisplayLink and I updated the firmware and it now works perfectly. Hope this helps!

I am using MacBook Pro 2017 and had same issues while connecting external monitor. I did SMC reset today. Right after the SMC reset, the issues were not resolved. Even I could't access wifi (especially, guest wifi) while connecting with the external monitor.

Several hours later, when MacBook is on sleep mode, I tried to connect with the external monitor and then I waked the MacBook up. Suddenly, the issue was resolved. I can use dual-monitor now. I am using two connectors: miniDP(RGB-HDMI) and a connector (HDMI-USB C). Hope it is helpful for you.

In summary, do SMC reset --> connect with external monitor when MacBook is on sleep mode --> wake it up.

Short term solution is to simple unplug the cdmi cable and then reconnect it. This will refresh the computer to see your external monitor. You will have to do this every time coming from sleep or a hard shutdown.

One cause might be that the 2016 MacBook Pro uses USB 3.1 over USB-C, whereas the 2017 model uses Thunderbolt 3 over USB-C. You might have better luck with a Thunderbolt 3 to DisplayPort adapter if you can find one.

I've had a problem that I think is related, in that I can't connect to an FTDI device from my 2017 MBPtb with an adapter, but I can connect to it just fine under the same OS with a 2012 MBPr. I suspect there's something going a bit wrong with the conversion from Thunderbolt 3 to USB.

Hello all,

Same here except I’m using a mid 2012 MacBook Pro. I can’t down grade because I upgraded to an SSD and didn’t use a time machine backup or anything. I spent over an hour with Apple while they went through the same things over and over and told me it was my fault in the end and dismissed me. Earlier they agreed it could be high Sierra and a software thing but later said to replace my cable even though it worked when I had Sierra. I know it’s not the cable. They also told me to contact the monitor company dell. I was so frustrated by this because I spent a reasonable amount of money on this monitor. Sorry for the rant but it’s all I got. Hopefully there’s a fix soon.

Thanks,

TJ

I had same effect on my Mac mini when upgrading to High Sierra. The software does not look for an external monitor. My fix is simply when Mac is up and running simply disconnect cable, then reconnecting cues software to see external monitor and sends signal to monitor.

I had this same issue. Before inserting the connector into your computer, make sure the USB port on the connector is open. If the USB port has a cord attached, the computer will not recognize that the charging cable is attached and it will go back into sleep after initially waking. Once the monitor is connected and the computer has awoken, you will notice that the computer is charging in the battery symbol. Then you may connect a cord into the USB port of the connector and you are ready to roll.

I have same problem with my Macbook 2015 running High Sierra 10.13 and 10.13.2 Upgrading to 10.13.2 did not help. Doing a PRAM and/or SMC reset also did not work. My external monitor attached via thunderbolt to VGA adapter was working fine... UNTIL i disconnected it to work elsewhere.... when I reattached it stopped working. I've upgraded displayport driver also and that did not help. I also found & attached via HDMI to external monitor and that ALSO does NOT work. External LG monitor does not find any signal on VGA nor HDMI connections 😟

I also downloaded the newest version of Display Link (http://www.displaylink.com/downloads/macos), ran it, restarted computer and it's working! The background on my MacBook screen changed, not a big deal in order to get my external monitor working again.

Same issue here! I bought a second iMac after in depth discussions with apple business as well as apple care about the compatibility of my mid 2011 iMac as an external display. EVERY place I looked and EVERY apple rep I spoke to said it supported the feature and was compatible even with the 4K. They are connected via apple USBC to lighting (again what I was instructed by apple to purchase) and when I select the "detect monitor" nothing happens. Hours on the phone with support and the best I have been told is that my cables may be faulty. I just migrated 252.94 GB of data from one to the other, via those cables, with no issue over the weekend. If they don't figure this out I am returning the new MAC and maxing out my ram on my old because this is BS. Sadly this is just the first of three major issues with high Sierra!

I had tried everything suggested in this discussion. Finally, I changed the cord I was using for my monitor from an HDMI-lightening cord, for which I was using an Apple lightening to USB-C adapter TO an HDMI-HDMI cord with an Apple HDMI to USB-C adapter. It seemed counter intuitive, but it finally works now. After two months of screwing around, it came down to the cord. (The old cord still works with my older macbook pro.) For me, it just came down to the right cord for my monitor. I would experiment, (save your receipts) and find the right one for you. Good luck!

Try power down , unplug, with 15 sec, replug, all devices. Turn on all devices, Then on Mac boot reset NVRAM & PRAM by holding down cmd/option/p/r simultaneously as soon as you hear the startup sound. Hold them until you hear it a second time. Once you sign in, both monitors should work as before. This worked for me.

I've experienced the same problem. I read on a third party blog, that if you can find someone with the same previous os - have them back up their mac, and you can restore your mac to that backup.

While you will get the old OS back, you'll also get everything that person had backed up as well.

This worked well for.

I was trying to connect an old Cinema Display (from about 2005) to a new (2017) iMac. I was using an Apple Thunderbolt 3 to Thunderbolt 2 adapter, and then an Apple Thunderbolt 2/Display Port to DVI adapter, but it didn't work. It works fine on my Airbook, though.

Then I tried using a Thunderbolt 3 to HDMI adapter, coupled with an HDMI to DVI adapter, then that worked and the old display is up and running.