2017 iMac 27 connecting to external displays

Hey guys - I have a Dell 27" monitor that worked for my 2013 iMac, but wouldn't work for the 27" I got last week. I bought a different cable than mentioned. It's an Amazon Cable Matters that is HDMI-Thunderbolt3/USB C. No matter what I tried nothing.

I called Apple Support and what they recommended WORKED. Here is what we did for my situation.

1. Power down your Mac.

2. Wait for it to completely power down, then unplug it for 30 seconds.

3. Plug it back in.

4. As you turn on the computer, hold down CMD-Option-P-R (yes, the keyboard letters P and R; 4 keys at same time).

The computer may make a sound, and if so, wait for 2 tones then release.

Oila! I'm up and running with my external monitor!

Jeff

Ok, so went and got the Apple Brand Multiport adapter and tried the HDMI and USB-C port, both had the screen blanks going on during startup and login.

So, went with a 3rd option, the https://www.amazon.com/gp/product/B06XNWLP89/ref=oh_aui_detailpage_o00_s00?ie=UT F8&psc=1 cable which is USB-C to HDMI and it works!

So, mileage may vary it seems with the cables (or is it Apple <-- yes), so for anyone googling this or whatever, these are my results for hooking up a 2017 iMac 27" to an external display via USB-C (Thunderbolt 3) to an HDMI cable, ultimately driving an LG 27UD69P (great monitor!).

Edit: The cable I mention in the first post is the CHOETECH USB-C to DisplayPort Adapter Cable 4Kx2K@60Hz (4ft/1.2m) for 2017 iMac, 2017 to clear up any confusion on what paths I took.

Here's what FINALLY worked for me. ugh, it was so frustrating, I rad everyone's solutions and just couldn't make it happen. Multiple cables, adaptors zapping SMC nvram whatev's restarting etc, nothing But here's what worked -

I got this cable

CHOETECH USB-C to DisplayPort Adapter Cable 4Kx2K@60Hz (4ft/1.2m) for 2017 iMac, 2017

But it didn't work either UNTIL I did an SMC restart (shut down - unplug for 15 seconds - plug back in - wait 5 seconds - restart) WITH EVERYTHING UNPLUGGED IN THE BACK. After the restart (I had to plug my keyboard in to sign in) I plugged in the monitor and it worked.

I got that exact cable, and when I turn my iMac on or wake it from sleep, the main display and external both blink a few times before coming back on and kicking any windows I had on the external to the main.

I'm using a LG 27UD69P 4K monitor, and the display is great... just those screen blanks are annoying.

Trying a usb-c to hdmi adapter from amazon and trying the Apple usb-c to hdmi adapter today too. Will report it on results.

I just brought the same cable (https://www.amazon.co.uk/gp/product/B0744GWJ8X) to connect my iMac 2017 to a Dell U2913WM and it works. Only issue I have is power. If I manually power down the Dell monitor, it wont turn back on unless lead is disconnected or the imac is off.

I have the same iMac and spent a weekend trying to connect to a DVI monitor. Trial and error... but I did find this one worked Amazon.com: USB C to DVI Cable (4K@30Hz), CHOETECH (6ft/1.8m) USB 3.1 Type C (Thunderbolt 3 Compatible) to DVI(24+1) Cab… (ASIN B06XCFPQH5) just plugged it in. Unfortunately they are out of stock right now...

I finally found a solution to my problem trying to connect a 23" ACD to a 2017 iMac. The great support people at https://www.monoprice.com helped me to understand that the particular year of ACD I have is the culprit as Apple's timing built into the attached DVI cable to it is proprietary and ONLY Apple connectors will work. So if you have a cinema display with the cables on the back looking like the image below you will have to buy the following 2 connectors to make it work. I got them yesterday, connected everything and my ACD is working perfectly with my iMac.

Apple HDMI to DVI Adapter - Apple

and

USB-C Digital AV Multiport Adapter - Apple

It's a pricey solution but it works if your ACD looks like this on the back:

I have similar issue but on iMac 27 late 2013 with ThunderBolt2 and Cinema Display HD (aluminium case not LED). Connected. When I startup my Mac every morning the second monitor still black and the little power led doesn't start. A need to unplug from the ThunderBolt port, wait three seconds and plugin again. Only with this way I can see the second monitor turned on :-(

As said I think is a power up problem and the TB2 doesn't wake up the monitor from power standby.

I hope for a solution because the ACD is anyway a good display.

I have the new 27" iMac and have 2 27" LG 5k monitors hooked to it and not having any problems. Had the same 2 monitors hooked to the MacBook Pro 15" 2016 and sometimes it would flicker and I had to shut down the MacBook. LG has a screen manager app for the monitor that runs in the background. It checks for firmware updates an does a few other things too. I read that there was a firmware update for these monitors. After installing the app on both Macs no problems. As for hooking other monitors to the iMac... i don't know.

Apple how to use these monitors on your Mac:

Use the LG UltraFine 5K Display with your Mac - Apple Support

________________________________________________________________

LG info on these monitors:

http://www.lg.com/us/monitors/lg-27MD5KA-B-5k-uhd-led-monitor

________________________________________________________________

LG screen manger app:

http://www.lg.com/us/support-product/lg-27MD5KA-B#manuals

I then picked up an Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 adapter to use with the DisplayPort to DVI Adapter.

Guaranteed not to work.

https://support.apple.com/HT207266

"The Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter doesn't support connections to these devices:

• Apple LED Cinema Display
• DisplayPort or mini DisplayPort displays
• DisplayPort or mini DisplayPort adapters, such as Mini DisplayPort to HDMI or Mini DisplayPort to VGA adapters"

Have you tried contacting StarTech? It may be that the 2017 iMac doesn't support USB-C Port DisplayPort ALT mode, which may be needed for those adapters.

Belkin makes a HDMI adapter

http://www.belkin.com/us/F2**038-Belkin/p/P-F2**038/

that is compatible withg the 2017 iMac. You can the use a HDMI to DVI adapter, which should work because HDMI and DVI use the same video signals.

I have a similar cable the

USB-C to DisplayPort Adapter Cable 4K&60Hz 6ft/1.8m, ITANDA USB 3.1 Type C Male (Thunderbolt 3 Compatible) to DP Male 4K Cable for the 2016 MacBook Pro, 2017 MacBook, ChromeBook Pixel

But I cannot get it to work! I don't have the option on my imac Pro for a display arrangement! What did you do to get it to work?

Thanks to ownry for the link that told me I would be wasting my money with a Thunderbolt 3 to 2 adapter going to a dual link DVI monitor. Here is ownry's link again:

Connect external displays to MacBook Pro (2016) - Apple Support

Here is the section on DVI (with most excellent Evernote Skitch rectangles around the "WILL NOT WORK" sentence).

So in addition to the Apple thunderbolt 3 to 2 adapter not working, I can add one more adapter (repeat from my post above) that does not work (yet, still firmware-fantasizing) to dual link DVI monitors. = AllSmartLifeusb c to mini displayport.

to All who read this.

I am happy to report that I hooked up the

to my 2017 iMac USB-c port and the Display port on the Dell P2715Q 4K 27 inch monitor,

and......

drum rolll......

IT WORKS!!!! just like it is supposed to.

for those of you not reading my previous post above, here is what I ordered from Amazon:

CHOETECH USB-C to DisplayPort Adapter Cable 4Kx2K@60Hz (4ft/1.2m) for 2017 iMac, 2017

it was only $20!

Now what to do with extra USB-c to Thunderbolt adapter I paid $50 for....

$1,700 CDN is about what the US paying for these monitors when converted to USD. We're spending $1,299 for the monitors here. I bought the 2 monitors before March 1st. Apple had them on sell for $999.00 if you brought them before March 1st. After March 1st they went up to $1,200. $999 USD = $1,299 CDN.

As for hookup... using the thunderbolt 3 connection. You need a HDMI dongle from thunderbolt to make that work. I have one... I also have a dongle for my 2016 15" MacBook Pro that has HDMI, card reader, thunderbolt 3, USB C and 2 USB. Something like this...

Good luck - if you indeed get the same StarTech adapter as I did, you will be in great shape. You connect direct from the octopus cable that comes with each ACD 23. Do check back and let us all know. I am enjoying the setup enormously. Here is the image of my set up that didn't load previously.