New 4k LG monitor only has 800 x 600 setting when connected to 2020 MBP?

[TJ82]

Picked up the LG 43UN700 4k monitor and instantly the resolution was 800 x 600.

In the options for displays it's the only option available too.

Looks horrific.

Any ideas?

 

[Fishrrman]

Are you talking about an Intel or m1 MacBook Pro?
What display cable are you currently using?
What display input are you connecting to?
What is the display input set to?

You could:
Change the cable.
Change the connection scheme.

 

[TJ82]

Are you talking about an Intel or m1 MacBook Pro?
What display cable are you currently using?
What display input are you connecting to?
What is the display input set to?

You could:
Change the cable.
Change the connection scheme.

Intel one, just before the M1 was released. Using USB-C, the one that came with the monitor..

Yesterday after changing to top left port it all worked again.

This morning though, that port reverted back to 800x600p.

Just switched port on the USB-C connection to the right hand side and it gave me new options (but still not the best resolution like I had yesterday).

Now I get:

1600x900
1080p
720p

Just tried the bottom right hand side port, get option:

720p

Okay this is ridiculous, why do my different MBP ports give different resolution options!

 

[BrianBaughn]

Are these all of the resolution options you see if, in System Preferences>Displays, you hold down the option key when clicking the "Scaled" button?

 

[TJ82]

Are these all of the resolution options you see if, in System Preferences>Displays, you hold down the option key when clicking the "Scaled" button?

Unfortunately yes!

 

[Fishrrman]

Again... try a different connecting cable.

 

[joevt]

For Intel Macs, you can use the AGDCDiagnose command to see what the connection is (DisplayPort link width and line rate). For 4K, it should be four lanes of HBR2.

 

[TJ82]

Just spoke to LG support, they said it has to be a TB3 to TB3 lead, not USB-C for this setup to unlock the higher resolutions!

 

[joevt]

Just spoke to LG support, they said it has to be a TB3 to TB3 lead, not USB-C for this setup to unlock the higher resolutions!

It's not a Thunderbolt display therefore a Thunderbolt cable will not work, unless it's one that supports USB 3.1 gen 2 or DisplayPort Alt Mode.

 

[TJ82]

It's not a Thunderbolt display therefore a Thunderbolt cable will not work, unless it's one that supports USB 3.1 gen 2 or DisplayPort Alt Mode.

Oh my.

Got a Belkin lead yesterday too, to try until the TB3 arrives and it didn't work at all.

No connection recognised. https://www.amazon.co.uk/gp/product/B072L88ZFX/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

That one.

This is getting hopeless. What sort of lead should you use to get an MBP to 4k monitor working over a USB-C port?

 

[joevt]

Oh my.

Got a Belkin lead yesterday too, to try until the TB3 arrives and it didn't work at all.

No connection recognised. https://www.amazon.co.uk/gp/product/B072L88ZFX

That one.

This is getting hopeless. What sort of lead should you use to get an MBP to 4k monitor working over a USB-C port?

That cable should have worked.

Do the following command for every cable (change the file name for each cable) It will show if it's connecting correctly.
/System/Library/Extensions/AppleGraphicsControl.kext/Contents/MacOS/AGDCDiagnose -a > AGDCDiagnose_1.txt 2>&1

Try a USB-C to DisplayPort cable.

Try SwitchResX to see a list of resolutions and timings.

 

[Tozovac]

Did you get it to work?

 

[TJ82]

Did you get it to work?

Nothing fixed it. Tried a boatload of different lead types and brands now and all have the same issue.

Got hold of a 13inch MBP last night and tried that. Worked in 4K right away with both leads I had sitting there, USB-C and DP.

Both laptops running latest versions of Big Sur so now it’s looking like a 16 inch MBP issue specifically. Going to contact Apple again tomorrow.

 

[peta909]

I have 16" MBP 2019 (Big Sur OSX 11.4) with LG 43 UN 700. The default USB C cable comes with LG doesn't work. I have a spare USB C cable (labelled: Type C Gen 1 5A) that works. I managed to get it to only work with the bottom left TB3 (me facing the screen when its open). I guess LG's monitor is USB C compatible but not fully TB3 compatible. Sorry, I cant recall where I got my USBC C cable from.