External monitor problem iMac 2017 High Sierra.

Wait - talk me through that again? unplug the monitor form what? The Power, or the iMac? Do I unplug it while the iMac is off? Sorry - could you be more specific, as this issue is really starting to get me down...

This is ridiculous - this problem just didnt happen before! What has Apple done that has brought this about. Down to 1 monitor now - the 2nd one now also dead. So from 3 monitors to 1, and no one knows why..?

As annoying as this is, imagine the plight of the Mac Mini users who are experiencing this with their primary (ONLY) monitor. I have purchases a new KVM, EDID plug ins, EDID transfer plugs and now have a second new KVM on order. All because of an update to High Sierra.

Personally I have to choose between:

1 The painful process of downgrading a Mac Mini to Sierra

2 Moving it to a headless Mac Mini with an EDID plug in

3 Selling it to a non-KVM user and replacing with a Dell Win 7 Machine

I am still waiting the AppleCare email regarding Apple compatible KVM devices. It was supposed to be to me in 48 hours bit I am at 2 weeks and holding... my only response was a survey. My personal lesson learned from the video issues with external non-Apple video in El Captain, Sierra and High Sierra is to never again purchase an Apple device which does not come with an embedded screen, or when I may require a second screen.

As with USB 3, it really does seem that Apple limits compatibility testing to Apple products rather than the industry standard Itself. I‘m a really big Apple fan, but do not have the luxury of existing n a homogeneous all Apple environment for either my work or personal use.

You’re lucky that you got that far. Mac Mini devices are actually the biggest victims of external monitor issues, as we all ned external monitors and usually buy for use with a KVM, for which they theoretically were designed. That makes it even worse... the sole Mac which does not have an integrated monitor should obviously be the primary test case.

El Capitan broke VGA for me, so I replaced with a DVI KVM.

Sierra broke broke DVI for me, so I replaced with an HDMI KVM.

High Sierra broke my HDMI KVM video.

So I am now searching, trying and returning many devices (5 so far). I had the good sense to NOT permit my new Mac Mini to update, but do find the constant High Sierra update request messages to be somewhat insulting.

It is worth noting that an 8 year old junker Dell Windows laptop from work has existed happily in all 5 of my KVM environments over the past 8 years.

Thank you! I spent literally hours trying to find this fix. Many emails exchanged with J5Create (who knew nothing). Read your post, unlocked the drivers and I'm back in business with two external monitors! You're the best!!!

Running MacBook pro (early 2015) with High Sierra 10.13.2 and my Dell U2717 still denies to work :-( Read all messages in this thread, tried all tips, installed (and uninstalled) DisplayLink driver multiple times, tried all the different cables (HDMI-HDMI, USB C - MiniDVI, USB-C - HDMI, multiple adapters, various brands and nothing :-(

Unfortunately, the installation of the driver didn't work for me. Thanks anyway.

I have experienced this connection problem since OS X Sierra was upgraded to OS X High Sierra. I have been in touch with an Apple tech - but still no fix. I have tried everything but nothing works.

I am connecting a Thunderbolt (2) adapter from my Mac Mini (late 2012) to my television set - using n HDMI cable.

From what I have read, it seems as though High Sierra OS is at fault.

So many external monitor issues, but the most critical of all are the Mac Minis, which, by definition, use only external monitors. For us, it is not an annoying problem with our secondary monitor, but a complete barrier to use. Without a top menu and a dock it is game over.

After 5 Apple tickets and approximately 120 hours with Apple and/or at home reinstalling numerous macOS versions and purchasing and installing 3 KVMs and EDID preservation devices, we've definitively proven that the only reason that a 2012 Mac Mini was works with Sierra HDMI is due to remnants of Mavericks and other in place upgrades up to Sierra. High Sierra broke that. We determined this as several clean reinstalls of Sierra showed the Sierra video issues which did not exist on the long Mavericks to Sierra upgrade path.

El Capitan was my solution as it has a level of iCloud compatibility which is compatible with Sierra, High Sierra and iOS 11 devices. Essentially this means that I now need to lock down my cross device tech level to El Capitan, Sierra and iOS 11.x until such time as Apple announces root cause and resolution or I choose to sell the Mac Minis and adopt only Apple devices which ship with integrated screens. Fortunately I've never updated my Late 2014 Mac Mini to High Sierra and will not do so. After Sierra and High Sierra I clearly need to freeze tech for a few years so that it works for me, not me working for it.

It's really annoying. I have the same issue like many others. The thing is, if a cable works in a Dell with a NEC monitor in my case, why when I switch to my Mac pro the same cable HDMI to VGA doesn't work... It should be a software problem... I don't want to buy many cables to see if at least one may will work... Totally upset... Thanks to every contribution, but it seems that Apple doesn't care anymore...

I've given up on trying to use any thunderbolt to HDMI adapters. Nothing I try will work. Therefore, I have decided to purchase a good HDMI splitter (a 4 x port one that provides an ON/OFF switch for each port).

Hope that you finally get your connection working again).

Bye

I was running two displays on my MacBook Air with no issues.... I upgraded to High Sierra and only one works... It's an Apple issue and they need to get it fixed!

I have the same exact problem. Apple! Please fix this! Productivity is being greatly affected!

Same here and with 12 of my clients machines. All of them are now on one monitor when they dock at work.

This is such bull sh!($. They need to fix the issue now. It's obviously a well know issue at this point.