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User profile for user: codermike
codermike Author
User level: Level 1
4 points

My MacBook Pro M1 sends no video signal to my USB-C 4K monitor (LG 27UP850-W). Blank screen?

I have a 2020 13" MacBook Pro M1 running macOS Big Sur 11.4. When I connect it to my new USB-C 4k monitor, using the monitor's supplied USB-C cable, I get no video signal on the USB-C monitor when selecting the USB-C video source input. I've tried both USB-C ports on my MacBook Pro to no avail.


However, the power delivery is working and I am able to charge my MacBook Pro. The system report for USB also shows it as detecting my LG monitor, but I'm getting no signal. I've tried the standard troubleshooting (power cycling, etc.) and no luck.


    USB 3.1 Bus:

    Host Controller Driver:	AppleT8103USBXHCI

    4-Port USB 3.0 Hub:

    Product ID:	0x9c02
    Vendor ID:	0x043e  (LG Electronics USA Inc.)
    Version:	1.50
    Speed:	Up to 5 Gb/s
    Manufacturer:	Generic
    Location ID:	0x00200000 / 2
    Current Available (mA):	900
    Current Required (mA):	0
    Extra Operating Current (mA):	0

    4-Port USB 2.0 Hub:

    Product ID:	0x5411
    Vendor ID:	0x043e  (LG Electronics USA Inc.)
    Version:	1.50
    Speed:	Up to 480 Mb/s
    Manufacturer:	Generic
    Location ID:	0x00100000 / 1
    Current Available (mA):	500
    Current Required (mA):	0
    Extra Operating Current (mA):	0

    BillBoard Device:

    Product ID:	0x9c02
    Vendor ID:	0x043e  (LG Electronics USA Inc.)
    Version:	1.00
    Serial Number:	12********FGH
    Speed:	Up to 12 Mb/s
    Manufacturer:	Realtek
    Location ID:	0x00140000 / 4
    Current Available (mA):	500
    Current Required (mA):	500
    Extra Operating Current (mA):	0

    LG Monitor Controls:

    Product ID:	0x9a39
    Vendor ID:	0x043e  (LG Electronics USA Inc.)
    Version:	4.11
    Serial Number:	10*******415
    Speed:	Up to 12 Mb/s
    Manufacturer:	LG Electronics Inc.
    Location ID:	0x00130000 / 3
    Current Available (mA):	500
    Current Required (mA):	0
    Extra Operating Current (mA):	0


According to this YouTube video this is a well known problem with M1 MacBooks and the latest macOS. Are there any workarounds other than having to use a USB-C/DisplayPort cable? (which is what I'm doing in the meantime).


Thanks if you can help!


[Personal Information Edited by Moderator]

Posted on Jul 19, 2021 2:36 PM

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User profile for user: woodmeister50
woodmeister50
User level: Level 7
20,503 points

Posted on Jul 20, 2021 1:25 PM

You do not show what shows up under "Graphics/Displays" in System Report

when the LG is connected via USB-C.


The other thing is to try a Thunderbolt 3 cable or a Thunderbolt4/USB4 cable

instead of the supplied USB-C cable. Make sure they are power delivery capable

(should be if meeting specs).


As an aside, how is the display working otherwise via the USB-C/DisplayPort

cable as I am seriously considering the 27UP850 or the stripped down 27UP600

(doesn't have USB-C or adjustable stand but all else is the same) to save a few

bucks. Also, if you don't mind, which USB-C/DisplayPort cable are you using.

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User profile for user: woodmeister50
woodmeister50
User level: Level 7
20,503 points

Jul 20, 2021 1:25 PM in response to codermike

You do not show what shows up under "Graphics/Displays" in System Report

when the LG is connected via USB-C.


The other thing is to try a Thunderbolt 3 cable or a Thunderbolt4/USB4 cable

instead of the supplied USB-C cable. Make sure they are power delivery capable

(should be if meeting specs).


As an aside, how is the display working otherwise via the USB-C/DisplayPort

cable as I am seriously considering the 27UP850 or the stripped down 27UP600

(doesn't have USB-C or adjustable stand but all else is the same) to save a few

bucks. Also, if you don't mind, which USB-C/DisplayPort cable are you using.

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User profile for user: codermike
codermike Author
User level: Level 1
4 points

Jul 26, 2021 8:39 AM in response to woodmeister50

Forgot to answer this:

As an aside, how is the display working otherwise via the USB-C/DisplayPort
cable as I am seriously considering the 27UP850 or the stripped down 27UP600
(doesn't have USB-C or adjustable stand but all else is the same) to save a few
bucks. Also, if you don't mind, which USB-C/DisplayPort cable are you using.

My USB-C/DisplayPort cable worked perfectly fine at 4K/60Hz. It's just a AmazonBasics bi-directional USB-C/DisplayPort cable. I also tested the other direction (DisplayPort -> USB-C) with my Windows computer and that worked fine too.

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User profile for user: woodmeister50
woodmeister50
User level: Level 7
20,503 points

Jul 26, 2021 2:37 PM in response to codermike

I ended up getting the 27UP600 and using a certified USB-C to HDMI cable and it is working spectacularly once calibrated matches my M1 MBA very, very well. 27UP600 just lacks the USB-C and an adjustable stand and $100 less. I didn't think having USB-C and the adjustable stand (I can always get a world of different stands since it has a VESA mount) justified the additional cost since I already had a USB-C dock.


While it might have been beefy, not all USB-C cables are created equal as I have seen in many posts on this forum.

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My MacBook Pro M1 sends no video signal to my USB-C 4K monitor (LG 27UP850-W). Blank screen?

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