After the update of catalina 10.15.6 the external display stopped working

Unfortunately I have the same problem with my MacBook 16 inch. My Satechi USB-C to VGA stopped working after 10.15.6 upgrade.

When connect it, MacBook and external screens become black. Sometimes it blinks with desktop like it tries to switch, but it is black most of the time. I have Satechi USB-C to HDMI and I used them both before 10.15.6, but now when VGA is connected all screens are black. I think it is problem with EDID, and Macbook can not set the right resolution and refresh rate for VGA screen.

I excluded a faulty dongle, because I have Windows 10 installed in bootcamp and all screens work perfectly.

I have an old (14 days) Time Machine backup and I think it is the only way to go back to 10.15.5

Give these a try

Resetting the System Management Controller

http://support.apple.com/kb/ht3964

Reset your computer’s PRAM

http://support.apple.com/kb/PH14222

see also if you can get your hands on another cable to exclude a possible fault

Hello

Unfortunately, I have the same problem with Catalina 10.15.6. In version 10.15.5 everything worked perfectly.

In my case, I use 3 external monitors with the following adapters.

USB-C to HDMI (Apple-branded) https://support.apple.com/es-es/HT207806

USB-C to VGA (Apple-branded) https://support.apple.com/es-cl/HT207807

USB to VGA Converter (RadioShack https://www.radioshack.com/products/radioshack-usb-to-vga-adapter)

After updating Catalina, the USB to VGA (RadioShack) adapter shows the black screen. Apple-branded adapters work properly.

I opened 3 cases with Apple support and they didn't solve my problem. They recommended me to reset SMC, PRAM, start in safe mode, create a new user, but none of these recommendations could solve it.

Thinking that the problem was the USB to VGA converter RadioSHack, I bought 3 USB-C to HDMI adapters (Ditron-branded - made in China) to generate a new test set.

Ditron-branded adapters work ok when I connect them individually. But I can't get 3 external screens to work at the same time as they worked in Catalina 10.15.5

The tests I did are:

1.

Connect the 5 adapters individually (2 apple and 3 ditron) = All work ok

2.

Connect:

USBC HDMI adapter Apple-branded = Works Ok

USBC VGA adapter Apple-branded = Works OK

USBC HDMI adapter Ditron-branded = Not Working

3.

Connect:

USBC HDMI adapter Ditron-branded = Works Ok

USBC HDMI adapter Apple-branded = Works Ok

USBC VGA adapter Apple-branded = Not working

4.

Connect:

USBC HDMI adapter Ditron-branded = Works Ok

USBC VGA adapter Apple-branded = Works Ok

USBC HDMI adapter Apple-branded = Not working

5.

Connect:

USBC HDMI adapter Ditron-branded = Works Ok

USBC HDMI adapter Ditron-branded = Works Ok

USBC HDMI adapter Ditron-branded = Not Working

I realize that the problem is that Catalina 10.15.6 does not support the use of 3 adapters, regardless of how they are combined. They are ordered by a FIFO (first in first out) system. The first one you connect works supporting a maximum of two.

Several questions came up while testing. For example: if there were a maximum of adapters supported between HDMI and VGA technologies.

When I saw the menu: System Information + Graphics / Displays, I could detect the following:

The Apple-branded USBC HDMI adapter recognizes this as follows: Adapter Type: Apple USB-C Digital AV Adapter

The Apple-branded USBC VGA adapter recognizes this as follows: Adapter Type: Apple USB-C VGA Adapter

The Ditron-branded USBC HDMI adapter recognizes this as follows: Connection Type: Thunderbolt / DisplayPort

In this menu, I could see that Apple-branded adapters recognize them as adapters and Ditron-branded adapters as Thunderbolt / DisplayPort connection type. In this new version of Os Catalina, there will be a limit of adapters that can be combined between Apple USB-C Digital AV Adapter, Apple USB-C VGA Adapter, and Thunderbolt / DisplayPort?

The only test that remains for me to do is get several Apple USB-C Digital AV Adapters and Apple USB-C VGA Adapters and try different combinations but only with Apple-branded adapters.

This last test is very expensive, I hope they solve this problem.

Thanks for the posts here. I am glad to see I am not alone.

I have tried the suggestions from ilogger and saw the same results as Van_Fanner.

I have bootcamp installed on the laptop, so I tried booting into windows and the monitor/cable works correctly.

Same here too. What's interesting is that I have one monitor attached with HDMI and the other with a dongle to VGA. The HDMI monitor still works perfectly fine but nothing on the VGA. Hope a fix comes out soon.

A small update...

I turned off my Macbook, after working in BootCamp, with USB-C VGA dongle connected to monitor and lid closed. I turned it on by connecting charger to other port and guess what... I can see login screen on my old VGA Acer. Unfortunately when system started to load analog screen went off, then turned on black and HDMI screen tuned on but also went black. When unpluged USC-C VGA, HDMI screen showed login screen with loading bar somewhere in the middle. Driver? Last HDR update? I hope they fix this soon.

I'm absolutely livid about this.

After 10.15.3 was a disaster too. I'm tired of all the hours lost because of Apple's lax standards when it comes to its OS.

Does anyone know how to downgrade back to 10.15.5?

Hey, always back up even when not having trouble. Its always a great practice to ensure all of the hard work you put in and all of our precious moments (Pictures & Videos) are protected and stored in a safe place. ~Time Machine

if you want to isolate and prove its a Mac OS incompatibility issue or a "System Wide" glitch, Just test it without transferring data across after the install. Time Machine gives you the option to restore just data or you can do this manually but only after you prove that it does work even after a full Upgrade to Catalina.

I too have this problem. I have a CalDigit Pro and previously had two ACTIVE DP->VGA adapters coming out of the CalDigit Pro dock. Was working great with some other peripherals. But the minute after updating to 10.15.6 I can only get one working reliably. Very frustrating when it was working almost perfectly before 10.15.6.

Ok. Resetting NVRAM helped. But it's still sensitive to what order the displays are connected for some reason. They only work plugged in right to left. Not left to right. Which is odd. But at least it's sorta working again.

I had this problem on my Dell display as well (model U2715H), and downloaded / installed the DisplayLink MacOS Software from this page:

https://www.displaylink.com/downloads/macos

It got my display back online after rebooting.

I have a similar problem. Updated to 10.15.6 and monitors not working. It seems that all USB C ports are now inactive. HDMI and USB 3.0 still works but USB C ports are dead. Waiting for Apple Support to get back on how to fix

I have a similar issue. I have been using a Satechi Type-C Pro Hub Adapter for 2 years, with a direct HDMI monitor and a USB C to HDMI dongle (uni USB C to HDMI Cable), with both monitors working fine from the dongle. This adapter used both USB-Cs on a side of your MacBook. I then on the other side use an Apple HDMI / USB Dongle to supply power and the 3rd monitor. All was working great.

Since 10.15.6, I am unable to run the 2x HDMI via the Satechi dock, and I also upgraded to a caldigit ts3 plus, and with this I am unable to run 2x monitors going into the one connection it provides back to the Mac.

When I take the dongles and plug one monitor per dongle, per USB-C port, be it the CalDigit or the Satechi, I can only have 1 monitor in each port, but I can get all 3 running at once.

So, I can run 3x HDMI monitors if I have 1 dongle in its own Thunderbolt 3 port, but if you double up on a single port, this no longer works.

I thought the CalDigit was not powerful enough to run 2x monitors at once, but turns out it's 10.15.6. I dont have another Thunderbolt 3 Mac handy to test with on a lower version.

Sounds like a 10.15.6 issue to me.

I just upgraded to 10.15.6 from 10.15.5 - turns out this was a mistake. I have a 16" MacBook Pro and I have the same Problem now.

I use a USB-C to HDMI adaptor from Belkin and a USB-C to VGA adaptor from Belkin.

The HDMI Adaptor works fine. Only when I plug the VGA adaptor in the Laptop the previously connected displays (including the internal display) go in a loop where they light up for a fraction of a second before they turn black again.

I tried to plug in the VGA adaptor in all ports and various combinations with the HDMI adaptor and I encountered the same problem. I tried this with 5 different external monitors.

I am so ****** about this. This update is now almost a month old and there is still no fix. How is it possible that they publish an update that has a bug like this. I purchased a premium product for 6k and I expect not to deal with bs like this. Catalina was a mess from the beginning but that they sill f**k this up with updates a year after the release of the OS is outstanding.

I do have a backup but I don't really have the time to go back to 10.15.5 right now as It takes a bit to transfer 4Tb of data.

Oh and apple support also has no clue whatsoever and couldn't fix the problem. GREAT.

Same issue here. It's definitely affecting VGA monitors. I have two displays HDMI and VGA, when the HDMI is plugged in alone all is well, once the VGA gets plugged in the HDMI and the MacBook Pro built in flicker on and off to black. VGA alone gets no signal.

I was able to switch the VGA to an HDMI and now I have all my monitors back.

I'm using VGA and HDMI loosely, because that is the actual monitor connection - all of my external displays go into a DVI adaptor that then connects to the laptop via USB-C.