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Connecting LG UD68-P to 2016 15-inch MacBook Pro for 4K/60Hz

Dj64Mk7

Dj64Mk7

macrumors 65816
Original poster
Sep 15, 2013
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Hi! I have been trying to connect my LG UD68-P to my 2016 15-inch MacBook Pro. Trying both HDMI and DisplayPort, I have been unable to reach 4K/60Hz or even 60Hz at any resolution.

I tried SwitchResX, but that still doesn't enable 4K/60HZ.


Thanks for the help, and sorry if this is in the wrong thread.
 
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xylitol said:
What adapter+cable or adapter cable are you using? You need either

https://www.amazon.com/Plugable-DisplayPort-Chromebook-ThunderboltTM-3840x2160/dp/B01EXKDRAC
or similar,
or
https://www.amazon.com/Anker-Adapter-Supports-Macbook-Chromebook/dp/B01MYUCWOK
or similar and a High-Speed HDMI cable (Apple recommends Premium Certified HDMI cable)
https://support.apple.com/en-us/HT206587
Click to expand...

I am using the DisplayPort cable that came with my LG monitor, connected to an Elgato Thunderbolt 3 Dock.
 
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Ok. What is your aspect ratio on the monitor? If it's set to Wide, I believe you're limited to 30Hz.
 
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xylitol said:
Ok. What is your aspect ratio on the monitor? If it's set to Wide, I believe you're limited to 30Hz.
Click to expand...

Ratio is set to Original. Turning on the setting for DisplayPort 1.2 causes the monitor to go into a loop of acting like it has a signal, and then saying no signal after displaying a black screen for a few seconds.
 
I just noticed from an earlier thread that you've had this problem already in April (so it's not High Sierra related). You must have tried all the obvious things: bad cable, loose connection etc. Anyway, here goes one more. In System prefs > Displays > Display, does it help if you hold Option-key when clicking Scaled?
 
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xylitol said:
I just noticed from an earlier thread that you've had this problem already in April (so it's not High Sierra related). You must have tried all the obvious things: bad cable, loose connection etc. Anyway, here goes one more. In System prefs > Displays > Display, does it help if you hold Option-key when clicking Scaled?
Click to expand...

Alright, here's what I found:

Running the panel at full 3840 x 2160 res (in non HiDPI mode) locks at 30Hz
Running at 1080p (HiDPI) is also locked to 30Hz
Running at 2560 x 1440 (non-HiDPI) locks at 59.88Hz
Running at 720p (HiDPI) is locked to 59.88Hz

Basically, running a non-HiDPI resolution results in a bump to ~60Hz; generally, running a HiDPI resolution (except in the case of 720p HiDPI) or the panel's native res results in a paltry 30Hz.
 
Advice by me given in other threads, from my own experience and plenty of tests with my multi-tester. Get a cable that complies with VESA, and one that specifies 2160p. LG, Plugable, and Anker cables aren't in the DP database; I've owned cables by all three companies and I have several SRX licenses - replace that cable with a Belkin/Accell/StarTech cable, and ditch SRX and the DisplayID profiles it created for your display. In my company - it's mine, I pay the bills - there are some 60+ displays in my shops and the only ones we had zero issues with were several Eizos, which shipped with VESA/DP-compliant cables. Get a 2160p cable - you want as much throughput as you can get. My 6 4k displays - 2 Dell and 4 BenQ, zero issues after a switch to Accell cables. Questions, look up my posts, lots of detail…
 
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xylitol said:
In addition to getting a good cable, reset your Mac's NVRAM
https://support.apple.com/en-us/HT204063

Also unplug the monitor from the mains for a few minutes.

I wonder if this is related (even though you've had the problem since Sierra):
https://forums.macrumors.com/threads/monitor-no-longer-does-4k-60-high-sierra.2072139/
Click to expand...

Reset NVRAM, and posted in the other thread. Can't get a different DisplayPort cable without jumping through hoops, as the monitor + the Mac itself are government-leased equipment. Although if LG was to determine that it is an issue with the monitor itself, it would be on me to arrange the service.
 
That Apple adapter doesn't support 4K@60Hz.

A good DP cable doesn't cost much, although it still leaves the Elgato dock as a possible culprit.
 
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xylitol said:
That Apple adapter doesn't support 4K@60Hz.

A good DP cable doesn't cost much, although it still leaves the Elgato dock as a possible culprit.
Click to expand...

Part of my reasoning in thinking it's the monitor is that turning on the DisplayPort 1.2 setting does nothing except make a black screen on the monitor.

Otherwise, the connection between the monitor and the dock is all DisplayPort to DisplayPort.

Or maybe I'm misunderstanding you. If that's the case, I'm sorry for not following along.
 
Sure, but obviously your DP to DP cable can be faulty. The dock can be faulty. The monitor can be faulty. The Mac can be faulty. It's not possible to solve the problem just by thinking, you have to make experiments (at least one) with different equipment: new DP-DP cable or a cable that bypasses the dock or another Mac/4K-source or another monitor etc. You tried connecting via HDMI, and I pointed out why you couldn't get 4K@60Hz with that experiment.

Of course, it would help if you have a friend who can loan you this stuff. Or who can test your stuff, starting with that supplied DP to DP cable.

BTW, here's an example where LG's supplied cable was faulty:
https://9to5mac.com/2016/06/04/lg-27ud88-w-usb-c-4k-monitor-macbook-review/
 
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