external monitor not being detected by MacBook Pro 2019

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

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

If not, your display adapter may be defective.

I recently purchased a 2020, 16-inch MBP to replace a 2008 16-inch MBP. I wanted to connect my new MBP to an external monitor (LG 27" UHD 4K, Model 27UK850). I purchased a "digipower" 7-port direct connect USB-C hub to use with the MBP. The USB hub has an HDMI out which was my preferred method of connecting to the monitor. When I initially tried to connect the monitor, it took some messing around with the connections but I eventually got the display to work and things were fine for the first two weeks. I then acquired a new, AUKEY, 10 port USB-hub to connect multiple external drives to my MBP. When I did this my LG monitor quit working and nothing I found on this thread or any other trouble-shooting sites seemed to help. I was growing very frustrated. Eventually I tried plugging in my Apple provided USB-C power cable into the USB-C port on the "digipower" adapter and the LG monitor suddenly came to life. Here is what I think is going on.

The "digipower" adapter does not receive enough power from the MBP to be able to push a strong enough HDMI video signal to the LG monitor. Once I connected the additional USB-C cable feeding power into the adapter it was then able to provide enough voltage to transmit a stable enough video signal across the HDMI cable to the LG monitor to allow it to work. I have replicated the problem several times, reliably. As soon as I disconnect the Apple USB-C power cable the LG monitor immediately dies. I believe that when I initially got the computer, my old USB hub for my external drives probably provided enough voltage to the "digipower" adapter to allow the HDMI connection to work but once I switched to the AUKEY 10-port adapter, there was not enough voltage provided to the "digipower" adapter to allow it to work.

So, my recommendation is when all these other steps fail, check your power input into whatever video adapter you are using to get the video feed into your monitor. Try plugging in either another powered USB-C or standard, powered, USB 2.0/3.0 connection and see if that won't help get your video signal to the monitor. It has fixed my issue. Good Luck!

Yes indeed, an explanation from Apple would be really calming, as I purchased a Display Port Cable that worked for the last 10 days, but stopped working yesterday too.

And still, the monitor works using any of the cables (usb c, usb-c to diplay port, usb-c to hdmi) with a Windows laptop that is 6 times cheaper than this Macbook Pro 16".

Update: Resetting NVRAM (https://support.apple.com/en-us/HT204063) does fix the issue partly, as now it works with the usb-c to display port cable, but still doesn't work a single usb-c or an usb-c to hdmi cable. (And it's also not too convenient to reset the NVRAM every 10 days to get it to work...)

I have the same problem. Wont detect any display Ive tried 3. Spent over 3 hours on Apple Support calls over 3 weeks.

NVRAM resets Safe Mode Boot, multiple cables multiple connectors including Apple Connector. Sleep mode to awake. The arrangement tab wont show up at all. Im ready to get a sledge hammer and see if that makes a difference.

Apple Support Engineering has combed through 3 downloads with the support group. The delays kill me when they go off for 5 days and I have to wait till they get back from their break. Talk on Monday then they cant get back until Friday. They do one action then wait another 4 to 5 days.

Ill repost if anything get resolved but Im losing patience.

Yes. But that response confuses me. Arent we supposed to update to the current Apple updates for all kinds of reasons secuirity bugs etc. It feels like Apple is back in the 1980s like when Microsoft was making everyones life a problem.

I tried going to a previous version with Apple Support desk I think. Not quite sure what they were doing but they said they were reverting to the default system that it was shipped with in Jan of 2020.

Thanks for the response. I think I might agree after looking at multiple reviews. The hard thing is this missing arraingment tab that never shows up and the OPTION Detect Display. Ill sit here and tap that button hundreds of times thinking it will eventually work. Ive bought 4 different dongles between HDMI and VGA Ive tried 5 different monitors including a new TV HDMI.

I bought a LG 4K Ultrafine display from the Apple Online Store and encountered the same problem when I connect it to my MBP 2017. I have installed the latest Catalina update this morning and there is still no response from the external monitor. I did not expect any compatibility problem like this with something I bought from the AOS...and at this price...

I just bought a Samsung U28E590D and do have a new Macbook Pro 16" with the latest Catalina. Same for me, can't see the external monitor and have tried different things that where recommend elsewhere. Might see if the cable or adapter is the problem.

Would be great if someone from Apple could respond to this and provide an update.

Ulrike wrote:

...

Would be great if someone from Apple could respond to this and provide an update.

Apple Support Communities provides Community support -- support from other Users like you.

If you want answers from Apple employees, the only way to get those is through the "Contact Support" link conveniently located at the top of every forum page.

system preferences > displays

Hold down the Option key and click on the (Detect Displays) button that should appear there (lower right corner).

Are you guys using Catalina 10.15.4? Seems that this version is causing problems to external monitors...

Any updates on this? 2019 Macbook Pro 16" with Dell U3219Q doesn't detect screen via usb-c. It does work with a Windows laptop with the same cable.

Just a quick update from me. I could solve it by not using an adapter but buying a HDMI to USB C cable. Works perfectly now :-)