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MBP 16" not connecting to display via usb-c to DisplayPort cable

O

Octavzz

macrumors newbie
Original poster
Sep 29, 2020
26
3
I have an MBP 16" 5500M 4GB, and I used to connect it through hdmi and the apple hdmi adapter. I wanted better refresh rate as my monitor can go to 1440p 144hz, so I decided to get an usb-c to Displayport cable, but unfortunately, my monitor won't recognise any input.

I tested the cable with my PC's GPU and the cable works, as well as the monitor in both hdmi and DisplayPort connections, so I am left out to believe the issue is with my MBP 16". I have tried some fixes around like restarting, connecting cable in clamshell etc. but I still can't figure it out. The cable is not the issue apparently, neither is the monitor.

What should I try to get DisplayPort working on my MBP 16"?
 
Can you go back to your original connection setup?
Does it work then?

I would try a "factory reset" of the display (with the computer OFF), using the display's on-screen controls.
 
Fishrrman said:
Can you go back to your original connection setup?
Does it work then?

I would try a "factory reset" of the display (with the computer OFF), using the display's on-screen controls.
Click to expand...
If I switch to HDMI, then it works ok, except having to deal with lower refresh rates and the notorious overheating when connecting external displays to the 5500M.

I want specifically to make it run on DisplayPort.

I will try a factory reset of the monitor and will update if it helped

EDIT: Didn't work.
 
Last edited:
I read that someone have to use usb-c dock with external power to "feed" that DP 144hz output. Maybe macbook didn't delivery enough power to drive that connection ?

HDMI 2.0 support 144hz but you should use only usb-c to hdmi cable - not with addition usb-A ports - but your monitor have to support via HDMI.
 
imp3rator said:
I read that someone have to use usb-c dock with external power to "feed" that DP 144hz output. Maybe macbook didn't delivery enough power to drive that connection ?

HDMI 2.0 support 144hz but you should use only usb-c to hdmi cable - not with addition usb-A ports - but your monitor have to support via HDMI.
Click to expand...
Even if higher refresh rates are not supported, it should still work at 60hz through DP. Instead, it does not work at all.
 
And MacOS detect connected monitor in Settings ? Can you set 60hz Refresh rate in settings ?
 
If I connect my monitor via HDMI, yes it works as intended except MBP 16" gets super hot.
If I connect my monitor via DP to USB-C cable, neither macOS or the monitor recognise the connection, it's like I haven't plugged anything in.
 
What cable do you use ? Do you have specifcation or link to it ? Your GPU in PC probably have an USB-C port and support Display Port altmode output.

Macbook doesn't support DP alt mode. Cable or adapter have to get Display Port signal from Thunderbolt 3 (same as your usb-c - HDMI cable do - but internaly - convert DisplayPort to HDMI).

Can you try other usb-C -> DP cable ?
 
imp3rator said:
What cable do you use ? Do you have specifcation or link to it ? Your GPU in PC probably have an USB-C port and support Display Port altmode output.

Macbook doesn't support DP alt mode. Cable or adapter have to get Display Port signal from Thunderbolt 3 (same as your usb-c - HDMI cable do - but internaly - convert DisplayPort to HDMI).

Can you try other usb-C -> DP cable ?
Click to expand...
I bought the cable based on a review that stated that it works with a MacBook. Did DP alt mode support drop in this generation of Macbooks, or it hasn't ever been supported?
 
It hasn't ever been supported. They use "native" display port output, which means that thunderbolt 3 can output native DP signal via TB3 data lanes. So you can connect Usb-c -> usb-c via thunderbolt 3 and that connection is same as DP to DP... or usb-c display port cable which "extract" display port data from TB3 and put to DP port in monitor...
 
imp3rator said:
It hasn't ever been supported. They use "native" display port output, which means that thunderbolt 3 can output native DP signal via TB3 data lanes. So you can connect Usb-c -> usb-c via thunderbolt 3 and that connection is same as DP to DP... or usb-c display port cable which "extract" display port data from TB3 and put to DP port in monitor...
Click to expand...
Thanks, I will look into getting another cable, will return this one, although I find it quite strange that this exact same cable has worked with another MacBook.
 
imp3rator said:
It hasn't ever been supported. They use "native" display port output, which means that thunderbolt 3 can output native DP signal via TB3 data lanes. So you can connect Usb-c -> usb-c via thunderbolt 3 and that connection is same as DP to DP... or usb-c display port cable which "extract" display port data from TB3 and put to DP port in monitor...
Click to expand...
Any USB-C port (Thunderbolt or otherwise) that outputs video is using USB-C DisplayPort Alt Mode.
The HDMI adapter is using DisplayPort Alt Mode. It has a DisplayPort to HDMI converter inside.
If the MacBook Pro gets super hot using the HDMI adapter, it will get super hot using any video output.

Octavzz said:
Thanks, I will look into getting another cable, will return this one, although I find it quite strange that this exact same cable has worked with another MacBook.
Click to expand...
The MacBook Pro has four Thunderbolt ports. Did you try all of them?
Did you test all the ports with any USB (2.0 and 3.x) or Thunderbolt device?
Maybe your MacBook Pro needs repair.
 
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joevt said:
Any USB-C port (Thunderbolt or otherwise) that outputs video is using USB-C DisplayPort Alt Mode.
The HDMI adapter is using DisplayPort Alt Mode. It has a DisplayPort to HDMI converter inside.
If the MacBook Pro gets super hot using the HDMI adapter, it will get super hot using any video output.


The MacBook Pro has four Thunderbolt ports. Did you try all of them?
Did you test all the ports with any USB (2.0 and 3.x) or Thunderbolt device?
Maybe your MacBook Pro needs repair.
Click to expand...
I did try all of the ports, but all ports behaved the same. I don't believe my MacBook needs repair though, as any other devices work as intended.

I just returned the cable as it is of no use to me if I cannot use it with my MacBook.

I will keep on searching for another DP to usb-c/thunderbolt cable. Any recommendations for one that is tried and tested with the MBP 16"?
 
Octavzz said:
I did try all of the ports, but all ports behaved the same. I don't believe my MacBook needs repair though, as any other devices work as intended.

I just returned the cable as it is of no use to me if I cannot use it with my MacBook.

I will keep on searching for another DP to usb-c/thunderbolt cable. Any recommendations for one that is tried and tested with the MBP 16"?
Click to expand...

Same issue here!
I tried StarTech USB C to DisplayPort 1.4 (CDP2DP146B). It works fine on MBP 13" 2016, but not on MBP 16" 2019. Laptop doesn't detect the monitor, and the monitor doesn't detect any signal.

I don't understand how it works on MBP 13" 2016 but not on 16" while both are Thunderbolt 3! It's strange.
 
I have the same issue here with my MacBook pro 16" 5500M 2019.

I just bought the Moshi USB-c to DisplayPort cable which can be bought in Apple store and tried to connect it to my external monitor ASUS VG27AG. My Macbook pro also doesn't detect any monitor and my monitor just has a message said the displayport has no signal.

However, my newly bought Lenovo legion 7 laptop has no issue connecting the monitor using the exact same cable.

Did you guys find you any ways to connect external monitors? I am trying to upgrade to Big Sur now.
 
gm292347 said:
I have the same issue here with my MacBook pro 16" 5500M 2019.

I just bought the Moshi USB-c to DisplayPort cable which can be bought in Apple store and tried to connect it to my external monitor ASUS VG27AG. My Macbook pro also doesn't detect any monitor and my monitor just has a message said the displayport has no signal.

However, my newly bought Lenovo legion 7 laptop has no issue connecting the monitor using the exact same cable.

Did you guys find you any ways to connect external monitors? I am trying to upgrade to Big Sur now.
Click to expand...

**** after I upgraded to Big Sur, it actually solved the problem!!!! thank god!

It must be the mac os issue.
 
I was already using Big Sur and I had this issue, but my problem disappeared after installing the very latest update (version 20E232).

What's new in the updates for macOS Big Sur - Apple Support

macOS Big Sur updates improve the stability, performance, or compatibility of your Mac and are recommended for all macOS Big Sur users.
support.apple.com support.apple.com

From the bug fixes section in the release note: "External 4K monitors may not display in full resolution when connected over USB-C"
It doesn't say it directly, but it solved the problem for me. Though, it has been only a couple of hours. If I see any issues, I'll drop a note here.
 
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