10.15.6, external display problem

My specs:

MacBook Pro (16-inch, 2019)

Processor: 2.6 GHz 6-Core Intel Core i7

Memory: 16 GB 2667 MHz DDR4

Graphics: Intel UHD Graphics 630 1536 MB

Built-in display: 16-inch (3072 x 1920)

Monitor: Dell D3218HN. Native resolution: Full HD (1080p) 1920 x 1080 at 60 Hz

Cable: Supports Ultra-HD video resolution up to 4K (3840 x 2160) @60Hz. Backward compatibility with 4K@30Hz, 1080p, 1080i, 720p

I'm finding that if I restart my MBP, then usually I can successfully connect the external monitor. However, if the display goes to sleep at all, then when I wake the MBP, both displays will flicker until I disconnect the external monitor.

@Grant Bennet-Alder - thank you for your help so far. You mentioned that "If your cable is not certified for the high speed of the display, it could fail to light up." Looking at the numbers here, it seems that my cable should be sufficient for my monitor (I am no expert though). Do you have any thoughts about what might be wrong in my case?

to get a Mac display to become active, you need the Mac to query the display, and the display to answer with its name and capabilities. Otherwise, the display will not be shown as present, and no data will be sent to the display.

This query is only sent at certain times:

• at startup

• at wake from sleep

• at insertion of the Mac-end of the display-cable, provided everything on that cable is ready-to-go

• on invoking Option-(Detect Display) button in Displays preferences (from another display)

so try doing some of those things and see if the display comes alive.

Modern Displays with multiple ports are sometimes busy scanning the other ports, looking for an input, and miss the query from the Mac. They need to pay attention to the port you are actually using, or they will miss the query.

Some displays have On-Screen Display settings that can be used to tell the display a computer is attached on a certain port, or a certain port should be highest priority. Changing those may make your display more responsive.

N.B.>>

Some displays include their own private "sleep" settings for the display alone. This can allow the display to enter its own sleep mode, on top of the Mac's not sending it data. A display that is sleeping on its own cannot respond to the Mac's query, and will stay dark.

Thanks for the info Grant. What you wrote seems to be geared towards a display that is unresponsive, or that can't be detected by the Mac.

However, I'm experiencing a different problem. As soon as I connect the external display, both the MBP display and the external display go into a dark flickering mode (meaning, both displays are mostly dark, but there are ongoing flickers on both screens showing what would be the correct display). This is also what others have been describing as a result of the 10.15.6 update. The display is connected to the Mac (during the flickers, I can see that it's listed in the Displays preferences) and it is sending data (because I see my MBP's desktop flickering on the external display).

Do you have any thoughts on what could be causing this?

This is my issue as well. It’s impossible to troubleshoot while the monitor is plugged in because you cannot see anything on either et screen I tried the clear ing of the NVRAM. Restarted in safe mode, tried every port on the laptop o could, to no avail.

I have a MacBook Pro 16 inch 2.6ghz 16 GB Ram system running 10.15.6

monitor is a viewsonic VA2431wm

Im also using a usbc to VGA converter so maybe Apple stopped support for VGA monitors?

if your displays have become mirrored, and the computed 'compromise' resolution is not very good for either display, you could end up with both displays flashing due to resolution a bit out of bounds, but almost good enough.

If you think the resolution is out of bounds, you can use Safe Mode to set it right. Safe Mode takes defaults for many things including display settings, but the changes you make in Safe Mode will "stick" in regular mode.

Safe mode is the same result. Both screens go blank and laptop screen flutters when the external monitor is plugged in. External display shows “no connection” for 3 seconds then goes black then shows again for three seconds and goes black.

very frustrating

It has been suggested that the graphics subsystem has always had the ability to test the integrity of cables used to connect displays. It is possible we are seeing Apple more-closely enforcing the correct standards.

There are three types of HDMI cables, but they are generally impossible to tell apart once they are out of the box;

Standard --

suitable for up to 1080i and 720p NB> this is nowhere near HD, which uses twice that data rate for 1080p

High speed --

suitable for 1080p, or 4K 2 30 Hz, not faster, and deep color at those rates

Premium high speed /Ultra High Speed --

REQUIRED for anything faster than 4K at 30Hz.

.

I also encountered the same problem right after upgrading the OS to 10.15.6.

I have a 2019 MacBook Pro, 16 in

I'm using an older LCD monitor with DVI output. It was connected via a Kensington dock with a DVI to DisplayPort adapter into the DisplayPort port on the dock. My intention was to be able to use two monitors with this dock. Before upgrading the OS, everything was working fine with OS version 10.15.5.

I called Apple several times but didn't get anywhere with them. So, I took my MacBook Pro and the Kensington dock to a local Apple authorized service provider. I asked them to check out the MacBook Pro and the dock and see if they could fix the issue or explain why it won't work. I picked up my MacBook Pro and dock today. I was told this is a "KNOWN" issue with the latest version (10.15.6) of Catalina. Unfortunately, the service provider said they had no remedy for me other than reverting my OS back to OS Mojave. But, I chose to stay with the current OS and work with the issue now that I know what's going on.

I was told to keep checking the support forum for news of when Apple fixes this. Who know's when that will be?

Before going to the local Apple service provider, I did a lot of troubleshooting. If anyone has any specific questions, I'll be glad to share more info.

Apple is milking the cash cows (that's US, its customers!). Go get yourself an *Apple* 69$/79€ USB-C to DVI adaptor and everything will be working again... And please throw away that ugly incompatible, now useless external hardware in a landfill...

As I wrote earlier: be prepared for an upcoming mandatory 50$ monthly subscription to Apple Services to be able to power up your 5000$ MacBook.

The following quote applies quite well to Apple: "Revolutions are started by idealists, continued by destroyers and completed by a tyran" (Louis Latzarus).

I received a call from Apple today (8/25/2020) with an update on this issue.

Apple now admits they are aware of this issue and are working on a fix for it. They told me the fix will come in an update to Catalina, possibly 10.15.7 or a supplemental update. No time frame was given for when the update will be released.

Hi there - I had the same problem with a screen using DisplayLinkManager (Asus Zen Screen) which I have finally resolved through the DisplayLink forum. This is the version of the driver to install if you're on Catalina 10.15.6 https://www.displaylink.com/downloads/file?id=1636

I've communicated with DisplayLInk tech support and they aren't able to assist with the issue.

Since Apple has stated there is a known issue with OS 10.15.6, I guess we'll just have to continue waiting for Apple to resolve this issue.

I resolved it by installing this version of Display Link Manager: https://www.displaylink.com/downloads/file?id=1636 But it took a few attempts, so you may need to install, uninstall a few times. Once installed, the relevant security box was automatically checked, and I'm back 100% fine on 2 screens.

Are you familiar with a "Passive" vs. "Active" cable or adapter? I wasn't until yesterday.

I was told to try an "Active" adapter instead of a "Passive" one, so I did and now my external monitor is working fine.

I can't believe the issue came down to the type of adapter!

I had the chance to try my Belkin adapter (Belkin USB-C to VGA adapter (F2CU037)) with a 13 inch 2016 MacBook Pro running 10.15.6 and it works totally fine with that. So this seems to be a problem with the 16 inch MacBook Pro.