External monitor problem iMac 2017 High Sierra.

High Sierra 10.13 Supplemental Update fixed it for me probably. Both external displays are now working (DP & HDMI).

UPDATE - the new DVI to HDMI cord did the trick. Purchased an off-brand name from Amazon for $7.

When you've started your Macbook, try to wait until you plug in your adapter. 10 seconds or so should do it. Then plug in your adapter AND wait another 10 seconds or so until you plug in your VGA, DVI, HDMI or whatnot.

I have to agree. A new monitor will not help this issue. This is clearly something Apple has to work out. I have one of the latest model MacBooks and a 2 new monitors, so buying a new monitor is not going to change anything. There is something that will get fixed. Use a Time Machine back up. I went back to Sierra and everything is working as expected! Don’t waist any money untill this issue is resolved.

Hey everyone,

I had the same issue, after upgrading to High Sierra my external monitors would only show the mouse and otherwise just be black. I use a wavlink usb3.0 docking station to hook up my monitors and external keyboard and everything. After spending a stupid amount of time looking through this and other forums and not being able to reset the SMC, I realized there was a really easy solution. UPDATE YOUR DISPLAY DRIVERS AFTER YOU'VE UPDATED TO HIGH SIERRA.

if you use a DisplayLink system: http://www.displaylink.com/downloads/file?id=1033

otherwise try downloading the newest driver for whatever external display you are using.

Hope this helps, otherwise, good luck!

This worked on a Macbook Pro 2013 with dual external monitors, one connected via HDMI and the other with a USB to HDMI adapter. Use the updated driver linked below!

From csdoyle > "if you use a DisplayLink system: http://www.displaylink.com/downloads/file?id=1033

otherwise try downloading the newest driver for whatever external display you are using."

Apparently, the last update (10.13.1) worked for me. I have my 2nd display plug via the HDMI to minidisplay port, and it's stable. I just notice that when the screen saver switches to another photo, it takes 1-2 sec to adapt.

I addressed that issue to my computer technician and he made me buying a new connector able to support HD and 4K (StarTechcom MDP2HD4KSW). Apparently, the old Apple connector I had was not able to do the job. So, this could help as well.

Hope it helps

Best

Eric

Weird suggestion (I hope temporary until Apple solves it) that worked for me is to disconnect HDMI from adapter, connecting it again and at the same time move and click the mouse/trackpad in the external desktop monitor. Somehow like "activating it".

As I said... weird but keeps me working on my external monitor.

Cheers!

It works!

NOTE: I was using two thunderbold outputs...and when I did that one of them didn't work, and had the same characteristics as describes above. I moved the non-working on to a USB output...and behold I have all my screens...so it seems that if I'm using a different "type" of port for each of my three externals, I work.

Yay! (ish)...just FYI for anyone else maybe experiencing the same.

Thanks all for the help.

I had the same problem. I finally solved this by getting better adapters. I got two of these http://a.co/53nOYaCand have two extra monitors working with my iMac 2017 27" What I learned is that all adapters are not created equally.

Feel your pain and same issue. Only thing that works for me is to unplug monitor and plug it back in while computer still on (not turn on and off with remote)

I changed my adaptor to this and im good

https://mackabler.dk/usb-c-5-in-1-hub-version-2-mini-displayport-475.html#/186-f arve-space_grey

Also using a thunderport to hdmi....

try resetting your SMC

[instructions copied from http://osxdaily.com/2010/03/24/when-and-how-to-reset-your-mac-system-management- controller-smc/]

If you run Time Machine backups just go back the point before installing High Sierra. Until apple admit/fix the problem then I see little point in upgrading. That's the only thing that worked for me done everything SMC etc.. and a fresh reinstall of High Sierra, none of which made any difference!!! Certainly would not spend any more money for something that appears to be Apple's fault.

Posting here incase this helps anyone else:

I too upgraded to High sierra today and then my internet and my dual screens didn't work anymore. Internet was a quick fix, but dual external monitors was not. I finally got it fixed when I reinstalled a driver for the dual monitors that I am using, mine happens to be Display Link.