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2017 iMac 27 connecting to external displays

I'm trying to set up a new 2017 iMac for a friend, and I'm having trouble connecting an external display to it. I first tried connecting an LG Ultra Fine 5K display using the supplied cable. It worked for a few minutes, and then it started flickering until it just blacked out. I tried a different cable (Belkin Thunderbolt 3) with no luck.

I also connected it to a ViewSonic 4K monitor through the Display Port using a Display Port to Thunderbolt 3 adapter. That monitor wouldn't even come on.

The weird part is that he was using both monitors with his 2016 MacBook Pro (has since sold), and they worked fine.

I have tried restarting as well as just shutting the iMac off before plugging the monitor in, even though I know I shouldn't have to. To be clear, I have only plugged in each monitor separately and never both at the same time.

I am at a loss. It appears to be an issue with the iMac itself, but I thought I'd post here in case this has happened to someone else and there's a fix, or I'm doing something wrong. Thanks in advance for your help.

The specs for the iMac - 4.2 GHz Core i7, 64GB RAM, Radeon Pro 580

Posted on Jun 24, 2017 3:44 PM

60 replies

billm

Level 1

61 points

Jun 24, 2017 6:05 PM in response to Eric Erickson

Have you tried zapping the pram command+option+p+r after you hear the startup chime until you hear the startup chime a second time. I have a 2017 27" imac which I'm about to start trying to connect to an external monitor via Thunderbolt 3 to displayport adapter. When Macs get confused, the PRAM stays confused until you reset it.

Jun 24, 2017 11:55 PM in response to billm

Thanks for your help! Zapping the PRAM doesn't appear to have worked, but does your 2017 iMac have a startup chime? This one is as quiet as the 2016 MacBook Pro. I've tried: sudo nvram BootAudio=%01, but no luck. I'm used to waiting for the chime and then second chime like you said, but without one I just went by the light of the screen.

Were you able to get your external monitor connected successfully?

Jun 29, 2017 1:52 PM in response to Eric Erickson

I have had a similar issue with a brand new iMac 27". No signal detected using a USB 3.1 Type C to DisplayPort 1.2 UHD adapter (made by Club) to a brand new BenQ BL2711U.

Reading many posts, it seems hooking an external monitor to this computer has been a nightmare.

As you can see from Apple's website the USB-C Digital AV Multiport Adapter has a rating of 2 stars.

If anyone out there can recommend a flawlessly working adapter to connect the new iMac to an external monitor (HDMI or DisplayPort), it would be very much appreciated.

Cheers,

Jason

billm

Level 1

61 points

Jun 29, 2017 6:18 PM in response to Eric Erickson

Doh! No pram zapping chime. No chime at all. I just attempted to connect a 27" IPS dual link DVI display to my 2017 iMac using Apple's dual link DVI to mini-displayport adapter and a Thunderbolt 3 to mini-displayport adapter http://amzn.to/2upHYem which >>>>>DID NOT WORK<<<<<<.

Prior experience with Macs leads me to be philosophical. Pram zapping is critical to getting mini-displayport working well. And the fact that we have no pram zapping now leads me to *HYPOTHESIZE* that we've got a firmware update coming that may restore pram zapping. I have no data. Just from my experience working at Fortune 50 US tech company and my observing the section managers shipping firmware **** to secure their ship date bonuses, and then the real firmware releases in 6 more weeks. I was not at Apple. Again, I have no data. Just suspicions based on somewhat related experience.

And I'm going to try your Sudo trick and see if that works. Thanks for that! :-)

billm

Level 1

61 points

Jul 3, 2017 2:53 PM in response to billm

I've now attempted to use the Apple Thunderbolt 3 to Thunderbolt 2 adapter MMEL2AM/A US$45 + tax again with no luck. Plugging in the Apple mini-dvi to dual link DVI adapter to the TB3toTB2 does not elicit a *flinch* from the 2017 iMac18,3. The Apple mini-dvi to dual link DVI works fine, as tested on my MacbookPro9,2 Still hoping for that firmware update!!! ~billm

Jul 7, 2017 11:32 AM in response to ownry

Thanks for the excellent information. After taking my iMac (and my LG 5K display) to the Genius Bar, I figured out that the LG display suffered from the WiFi router issue. It worked because it was further away from the router. Unfortunately, moving it far enough away isn't viable now, and it shouldn't do that anyway. So I sent that to LG's repair service.

My other monitor that does not work is a Viewsonic 4K monitor. I used a Cable Matters USB-C/Thunderbolt 3 to DisplayPort 4K 60Hz Adapter that I bought from Amazon. This adapter worked great with a late 2016 MacBook Pro. Obviously, something has to be different with the TB3/USB-C ports on the new iMac or my cable/adapter died all of a sudden.

I'm hoping you have luck with the CHOETECH cable you bought.

digibudII

Level 2

491 points

Jul 7, 2017 10:42 PM in response to Eric Erickson

My EIZO monitor is DVI and connected to my old iMac with a DVI to display port adapter. No Tbolt3 to 2 adapter could get it to work with my 2017 iMac. After getting an OWC Thunderbolt 2 equipped enclosure my display connected just fine.

Jul 8, 2017 9:32 AM in response to Eric Erickson

I'm in a similar boat - have newest iMac 27 18,3 maxed out and want to connect 2 Apple Cinema Didplay 23 inch monitors. Has anyone successfully gotten an old Cinema Display to work with a new 3017 iMac?

Jul 11, 2017 9:27 PM in response to David M Brewer

I would have loved to buy the Apple endorsed 27" LG, but $1700 CDN is a little steep. You're going USB-C to USB-C.

I think the majority of issues are going from a Mac USB-C port to another monitor port like HDMI or DisplayPort.

Jul 12, 2017 11:36 AM in response to RHPODOLSKY

Both my Apple Cinema Display 23inch are now working with my Mid 2017 iMac 27! I used two StarTech USB-C (24pin) male input to DVI-D (29pin) female output and VOILA - both monitors are working and playing nicely with the 5K, 27 inch. I really didn't expect this to work! But it did. Not sure if this will work with Cinema Displays of larger sizes. Thanks to all the good advice here. Don't give up!

Jul 14, 2017 11:48 AM in response to RHPODOLSKY

Here is a pic of a 2017 iMac 18,3 driving two 23in Apple Cinema Displays. For a stress test I have macOS Sierra flanked by a monitor running Apple Mac OS 9 on the left and Windows 10 on the right monitor. Speaks to the power of the Radiin Pro 580! I probably should put on sun screen or screen screen. It's bright!!

snp.ltd

Level 1

4 points

Jul 18, 2017 2:40 PM in response to RHPODOLSKY

Thanks. Your set up is what I want to do. But how did you get OS9 to work on this new machine? Or is this screen sharing an older mac? Yes I ordered the StarTech.com CDP2DVI USB-C to DVI Adapter for video resolutions up to 1920x1200 (Black) from Amazon. It is the same model number as the one on the StarTech.com web site.

Jul 18, 2017 11:27 PM in response to snp.ltd

No screen-sharing. That is a live OS 9 running on the new iMac. I use an emulator called Sheepshaver to achieve that. I have some rather old but important (to me) OS9 software I need to periodically run. For Windows 10 I use Paralells emulator.

Also, I am trying to throw everything I can at this new iMac while I decide if I'm going to keep it or not. So far it looks great !! It's half the price and 6 months (st least), prior to the release of the iMac Pro.

snp.ltd

Level 1

4 points

Jul 20, 2017 9:54 AM in response to RHPODOLSKY

I still have a PowerMac G5 (2005) around with a partition to start up in Tiger so that I can use OS9 Classic for rare occasions. This was the last of the PowerMacs. Still works. Put in an SSD drive and 2GB drive last year. I should be receiving the USB-C to DVI adapters by Monday. Amazon's 2-day shipping turned into almost a week for some odd reason.

snp.ltd

Level 1

4 points

Jul 21, 2017 4:22 PM in response to RHPODOLSKY

Received delivery of one of the StarTech.com CDP2DVI USB-C to DVI Adapters I ordered. Plugged it in. It works! Thank you for the suggestion!

After I order these I found a cheaper version for $19.99 which I think should work. Monoprice Select Series USB-C to DVI & USB-C (F) Dual Port Adapter https://www.monoprice.com/product?p_id=15243

2017 iMac 27 connecting to external displays