LG 5k Display 2013 Mac Pro Sierra Issues

LG 5k Display 2013 Mac Pro Sierra Issues

I was excited when I saw the announcement for the LG 5k Display for Apple. I thought the footprint and features would be a great match for the work I do. I primarily use my 2013 Mac Pro for motion graphics and video editing. The day my LG 5k arrived, was a huge…disappointment.

After unboxing, I plugged the monitor in to my 2013 Mac Pro and…nothing. A black screen. I admit – this was my bad. I should have read the specs. The new monitor requires OS X Sierra. My MacBook Pro was already running Sierra, but hadn’t gotten around to updating my Mac Pro yet. The new mornitor was the impetus.

As always, I did a clean install. It always works so much better than doing an OS upgrade. Sure, it’s a bit more work, but personally – I believe it’s worth it. This time when I booted my Mac Pro with the new LG 5k – it worked. Sorta.

Sure. It powered on and it was semi usable. But It seemed to be plagued with problems, that I couldn’t pinpoint. For example, it constantly blinked to black. It wouldn’t shut down or restart without doing a hard shut down on the Mac itself. I had read that the blinking issue could be related to WiFi or router interference. To eliminate that variable, I tried working without internet, disabling the WiFi off in my office from the router. No luck. 

Since I had two new variables in the mix (a. the OS upgrade to Sierra and b. the new monitor), I had to determine which variable was causing the issue. I decided to try using the LG monitor with my 2016 MacBook Pro. It worked like a charm, so I turned WiFi and my router back on. It continued to work flawlessless without the screen going back. Because of this, I came to the conclusion that it must be my Mac Pro. Since it’s still under Apple Care, I decided the easiest way to resolve the issue would be to take it in to Apple.

With my Mac Pro out of commission, I started working on projects with my 2016 MacBook Pro connected to the LG 5k. It worked pretty well. For a day or two, I even considered selling my Mac Pro and just working with the laptop. But After Effects requires a lot of RAM. I guess I’ve spoiled being able to RAM preivew tons with the 64GB of RAM on my Mac Pro. This was the biggest downside of working on my MacBook Pro with only 16GB of RAM.

Spread thin on time, I wasn’t able to take my Mac Pro in to Apple. With a deadline looming, and the need for After Effects speed, I decided to troubleshoot the Mac Pro issue myself. Ultimately, I believe I have found the solution.

As outlined in Apple Knowledge Base Article HT5918, The 2013 Mac Pro has a total of three Thunderbolt busses, each powering Thunderbolt 2 ports and the single HDMI port. Based on old Macs with multiple PCI busses, thought one possibility might be that the LG 5k needed to be on it’s own buss. Below is a diagram for the Mac Pro Thunderbolt busses.

I unplugged all devices from my Mac Pro and LG 5k – including all USB2, USB3, and USBC devices. With a clean start, my goal was to continue to add back devices until the original problems started to occur. What I had noticed when I was having the issues, was that the Mac Pro would boot up – but more often than not, I wouldn’t see the Apple logo or boot progress bar, The screen would remain black until the login screen.

With a clean slate, I plugged the LG 5K monitor into Port 6 on Thunderbolt Bus 0 and booted up the Mac Pro. The Apple logo and progress bar appeared. I logged in and tested it for a while – all worked well. Since I obviously needed a mouse and keyboard, these were the next two devices I added, directly to the back of the Mac. I was able to shutdown and restart my Mac without and issue. I then moved the mouse and keyboard to an external USB3 hub, and everything continued to work without a glitch.

Next in order of importance, was my G-Speed Shuttle XL RAID – which is a Thunderbolt 2 device. I plugged this in to Port 4 on Thunderbolt Bus 2. Then I went through the same process of booting up and testing. All was good. 

I repeated the process, each time adding a new variable: ethernet, another external Thunderbolt 2 harddrive (Port 1 – Thunderbolt Bus 1), a small USB-C hub, in one of the LG 5k USB-C ports, and a USB-C drive in one of the USB-C ports.

The ethernet and the second Thunderbolt 2 drive worked like a charm. Even the small USB-C hub on the back of the LG 5K seemed to work pretty well. But adding a USB-C drive to the back of the LG 5K started causing issues again (blinking to black). I removed that device, and the USB-C hub, and have been using my Mac Pro for the past day now without any issues. 

Last night, I tried connecting an 8TB LaCie Porsche Design USB-C drive on connected to the LG monitor using the USB-C cable that came with the monitor. It too seemed to work fine.

In summary, I now have a working Mac Pro system with an LG 5K monitor. The key is to ensure the LG 5k is on it’s own Thunderbolt Bus. I also believe that USB-C cables are not made equal. If you’re planning to use the USB-C ports on the back of your LG 5k monitor, be sure you’re using a high-quality USB-C cable.

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