MacBook Pro 16 external display issues

I have been using my LG 38UC99 display with my old Macbook Pro without any issues. I recently switched to the new 16 inch Macbook Pro and now when the Macbook wakes up from sleep (most of the times) the display won't work. Switching the display port to a port on the opposite side of the Mac solves it sometimes, but most of the times I have to restart the Macbook to get the display to work. Otherwise my Macbook display keeps flashing while there is nothing on the external display. Looks like its trying to switch between the Macbook display and the external display on and off. Not sure how to solve this issue.

I have two different issues

1) With Thunderbolt display and apple branded dongle: The external monitor won't wake from sleep without repeated connect/disconnect

2) With Dell U3415W ad IOGear USB Docking Station Model GUD3C03: The external monitor wakes up washed out (see pic) or repeatedly goes to sleep and wakes up.

(Original Post here: https://discussions.apple.com/thread/250998764)

I've tried to contact support but they really don't want to do anything online. Guess I have to make a phone call. How 2002 of you, Apple.

Hello mamrotek,

Thanks for reaching out in Apple Support Communities! I understand you're having trouble with your external display. I'm happy to assist you with this.

Check out this article for troubleshooting steps to help resolve this issue:

Get help with video issues on external displays connected to your Mac

Thanks for using the Apple Support Communities, and have a great day!

I have the same problem with external display turning on and off. I use CalDigit TS3+ connecting to a 4k and a 1080p display. When I enable mirror displays, all displays turn off and on. The internal display turns on first and the other two follow later. Resetting nvram and smc does not resolve the issue. I first thought it was the problem of TS3+ so I ordered a replacement. But the issue is still there. Another issue that display won't turn on after MacBook going to sleep is discussed here: https://discussions.apple.com/thread/250888931?page=1

Okay after doing the Reset NVRAM or PRAM on your Mac – Apple Support I have been using the USB-C hub with the HDMI cable plugged in to the adaptor and everything seems to be okay now after 2 days.

So fingers crossed.

Why do I have difficulty with Wi-Fi or Bluetooth devices when USB 3 devices are attached to my computer?

Some USB 3 devices can generate radio frequency interference that can cause Wi-Fi and Bluetooth devices operating in the 2.4GHz band to have issues communicating with your computer. Here are some tips to avoid this issue:

• If your USB device has a cable long enough that you can move the device, place it away from your Mac—and make sure not to place it behind your Mac, or near the hinge of its display. The antennas for Wi-Fi and Bluetooth are located there, and USB 3 devices placed there might interfere with your wireless connections.

• If you're using adapters or dongles on a Mac computer with Thunderbolt 3 (USB-C) ports, plug them into the front port on the left side of your Mac, or into the ports on the right side (if your computer has them). These ports are the farthest away from the antennas, making interference less likely.

• To avoid interference on the 2.4GHz band using Wi-Fi, try using the 5GHz band instead. You can change this on your wireless base station. Bluetooth always uses 2.4GHz, so this alternative isn't available for Bluetooth.

from:

Using USB devices with your Mac - Apple Support

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Mr. Bennet-Alder,

I have read your responses in this thread and they seem almost designed not to help with the problem. This is an issue that is recurring for every single MBP16 owner I know and there are several threads on this on the support forms. (Another is here: https://discussions.apple.com/thread/250931552). It does not matter what adapter is used, what monitor is used, etc.

And yet you talk about RF interference and suggest basic items like Detect Displays.

From everything I can tell (from log files from the associated crashes this bug causes if a machine is left to sleep for long enough), this is a memory leak/display driver bug that is either AMD's or Apple's fault. No matter the fault, it is up to Apple to get it fixed and I'm flabbergasted, having been an Apple user for over 30 years, that this has been allowed to sit for four months without fixing it.

The number of crash reports that have been sent on this has to be in the thousands, just based on the ubiquity of the problem and the effect it has on any user with an external display. I would bet a hefty proportion of people buying a 3k laptop use external displays.

I check these threads multiple times a day hoping for relief. I am hopeful that the next turn of Catalina will fix this. But the idea of spending an hour on the phone with Apple tech support so that they can not solve the problem, which can only be solved by an OS update or maybe even a firmware update, is not something I'm willing to tolerate.

Apple really needs to fix this for its most loyal customers on a flagship product.

That movie shows your display going dark for about 8 seconds at a time. That is no ordinary problem.

For additional testing, you could enable [√] Mirror displays. This runs BOTH displays (using a compromise resolution) off the SAME display hardware, except for the last output, which you have already debugged by trying multiple output ports. If the internal display does not go off, but the external display does go off, that vindicates the internal graphics hardware.

My guess is that you have an interface problem, and should replace your adapter with a new one. The new MacBook Pro may be sending data far faster than the old computer ever could, and the adapter may be losing Sync.

For me exactly the same problems occur. Also with the Eizo display (@home) but also with HP display (@work).

The suggested solutions do not work.

Sometimes a reboot does works for a while.

This is really blocking me from working efficiently with the new mac.

For additional testing, you could enable [√] Mirror displays. This runs BOTH displays (using a compromise resolution) off the SAME display hardware, except for the last output, which you have already debugged by trying multiple output ports.

If the internal display does not go off, but the external display does go off, that vindicates the internal graphics hardware, and suggests the problem is occurring in the final output or the adapter.

If you have run exactly this experiment, Readers would love to hear your results.

Ok. Thank you for all of the ideas.

I’ve done some additional testing and the results were pretty much the same.

I’ve solved the problem by buying new adapter. The one that works well in this case is club cac-1510.

sticzed wrote:

...

I’ve solved the problem by buying new adapter. The one that works well in this case is club cac-1510.

...

That is good information.

But you never posted any other information on this thread, so we still don't know about other folks (especially the Original Poster) results for these experiments.

I have the same issue. On wakeup many times, the external monitor does not work. Sometimes changing the port fixes the issue. Other times it does not. VERY VERY unproductive to have to restart everything I want to use my external monitor after waking up. Frustrating with a brand new 16. Apple needs to fix this!!!