LG 38WN95C Thunderbolt issues with Macbook Pro M1

[PaulKemp]

LG 38WN95C Thunderbolt issues with Macbook Pro m1​

LG 38WN95C suddenly stopped working over thunderbolt a few weeks ago. It has been working perfectly with the M1 Macbook Pro 14" for 4 months with all bells and whistles. Native resolution at 144hz, mac charging and usb hub. Display works perfectly over display port to my other machine.

Have anyone got any tips or other ways to troubleshoot this?

Issue:

• When connecting Thunderbolt cable, the Macbook cycles through this procedure around every 5 seconds;
  • Starts to charge, "ding sound".
  • Super quick showing "Allow accessory to connect" (Can be seen in the attached gif)
  • Disconnects the charing.
• LG display not seen in detailed "System information" under Thunderbolt connections nor in the System Prefs "Displays".

Troubleshooting done

• Ran Mac diagnostics at startup, no isses found
• Tested booting in safe mode, the exact same thing happens.
• Replaced Thunderbolt cable, tested 3 total including the one that has been working the past 4 months. Changes nothing.
• Tested all 3 TB ports on the mac - same thing happens on all.
• Enabling System prefs -> Privacy & Security -> Always allow accessories to connect

System
Macbook pro m1 2021 with Ventura 13.1

I am currently awaiting a response from LG regarding this issue.

Normally, I though resetting SMC or NVRAM would help with this, but since this is a M1 mac, no dice.

Also posted this on the Apple discussions forums.

 

[satcomer]

LG 38WN95C Thunderbolt issues with Macbook Pro m1​

LG 38WN95C suddenly stopped working over thunderbolt a few weeks ago. It has been working perfectly with the M1 Macbook Pro 14" for 4 months with all bells and whistles. Native resolution at 144hz, mac charging and usb hub. Display works perfectly over display port to my other machine.

Have anyone got any tips or other ways to troubleshoot this?

Issue:

• When connecting Thunderbolt cable, the Macbook cycles through this procedure around every 5 seconds;
  • Starts to charge, "ding sound".
  • Super quick showing "Allow accessory to connect" (Can be seen in the attached gif)
  • Disconnects the charing.
• LG display not seen in detailed "System information" under Thunderbolt connections nor in the System Prefs "Displays".

Troubleshooting done

• Ran Mac diagnostics at startup, no isses found
• Tested booting in safe mode, the exact same thing happens.
• Replaced Thunderbolt cable, tested 3 total including the one that has been working the past 4 months. Changes nothing.
• Tested all 3 TB ports on the mac - same thing happens on all.

System
Macbook pro m1 2021 with Ventura 13.1

I am currently awaiting a response from LG regarding this issue.

Normally, I though resetting SMC or NVRAM would help with this, but since this is a M1 mac, no dice.

Also posted this on the Apple discussions forums.

That means it is formatted NTFS a Microsoft boot disk! If this new, reformat the drive!

 

[PaulKemp]

That means it is formatted NTFS a Microsoft boot disk! If this new, reformat the drive!

I am sorry, I dont understand what that means. The main drive on the Mac is APFS and no other storage is connected, flash or others.

 

[satcomer]

I am sorry, I dont understand what that means. The main drive on the Mac is APFS and no other storage is connected, flash or others.

NTFS is Microsoft ONLy format that only allows Mac OS to read only nfs drives even Linux guys are finding this fact! Like APFS in now the default for SSD Mac drives directly counted (DAS disks)! Mac OS then uses the older HFS+ for network drives (NSS disks)! as old Mac user I always had to reformat new drives from nontraditional vendors that primarily sold only to Microsoft users, that was just a fact of Life!

So if the drive is either HFS+ or APFS and is failing so you have to face that fact!

 

[PaulKemp]

NTFS is Microsoft ONLy format that only allows Mac OS to read only nfs drives even Linux guys are finding this fact! Like APFS in now the default for SSD Mac drives directly counted (DAS disks)! Mac OS then uses the older HFS+ for network drives (NSS disks)! as old Mac user I always had to reformat new drives from nontraditional vendors that primarily sold only to Microsoft users, that was just a fact of Life!

So if the drive is either HFS+ or APFS and is failing so you have to face that fact!

That might be, but that is not relevant to the fact that my monitor is not working over thunderbolt. No drive isses.

 

[satcomer]

What thunderbolt cable you are using? I ask because it might 3 or 4 cable and monitor needs one or the other! Does it have a manual you can use to see what able you should use!

 

[PaulKemp]

What thunderbolt cable you are using? I ask because it might 3 or 4 cable and monitor needs one or the other! Does it have a manual you can use to see what able you should use!

Tested both TB 3 and 4. Two brand new cables + the one cable that has been working perfectly for 4 months. So it is not a cable issue.

 

[stradify]

Sounds like you're experiencing a glitch with 'allow accessory to connect'.
Try this: Set 'Allow accessories to connect' to 'Always' and see if that corrects the problem.

Allow access to USB and Thunderbolt accessories​

By default, your Mac laptop with Apple silicon asks that you allow a new or unknown accessory to connect. To change this setting:

1. Choose the Apple menu  > System Settings.
2. Click Privacy & Security.
3. Scroll down and click the pop-up menu next to "Allow accessories to connect," then choose which option you want. Learn more about the options.

On supervised Mac laptops with Apple silicon, administrators can control this setting.

 

[PaulKemp]

Sounds like you're experiencing a glitch with 'allow accessory to connect'.
Try this: Set 'Allow accessories to connect' to 'Always' and see if that corrects the problem.

Allow access to USB and Thunderbolt accessories​

By default, your Mac laptop with Apple silicon asks that you allow a new or unknown accessory to connect. To change this setting:

1. Choose the Apple menu  > System Settings.
2. Click Privacy & Security.
3. Scroll down and click the pop-up menu next to "Allow accessories to connect," then choose which option you want. Learn more about the options.

On supervised Mac laptops with Apple silicon, administrators can control this setting.

Thanks for the detailed description and taking the time to write it!

I have tried this and it was also suggested by Apple support. However changing the setting does nothing (my bad for not writing this as part of the troubleshooting steps, I forgot).

When this setup works, it doesn’t prompt me to accept anything. That is when the display is getting recognized as a display. When it is buggy, I am getting the error seen in the gif.

I am getting more and more certain it is the display who is the culprit however I am still awaiting a response from LG.

 

[nancy415]

Thanks for the detailed description and taking the time to write it!

I have tried this and it was also suggested by Apple support. However changing the setting does nothing (my bad for not writing this as part of the troubleshooting steps, I forgot).

When this setup works, it doesn’t prompt me to accept anything. That is when the display is getting recognized as a display. When it is buggy, I am getting the error seen in the gif.

I am getting more and more certain it is the display who is the culprit however I am still awaiting a response from LG.

Hey Paul,

I have the EXACT same issue. I am using the 2021 MacBook Pro M1 Max 16". Troubleshot the same way you did.
Tried new Thunderbolt 4, restored the OS, used Recovery Mode, also purchased a new MacBook Air just to test it out.
I have already sent my MacBook twice for servicing. The first time I sent it in they replaced the logic board. Problem still persisted. Second time I sent it in, the replaced all the USB-C ports. Problem still persisted. Just yesterday I spent 1.5 hours on the phone with a senior advisor to CaptureData to send to the engineering team. I also video recorded the issue of the connection dropping and compared it to a MacBook Air M2 to show that there was no problem there. Just now I got a phone all from the senior advisor and she said the engineering team suggests I change the refresh rate of the monitor to 60hz. As soon as we got off the phone, the problem started again but this time it only drops every few minutes vs. every 5-ish seconds.
She's going to call me back tomorrow again to check in and I will report to her that the connection still drops. I tried to reply to your post in the Apple forums but it's closed.

Have you heard back from LG?

 

[nancy415]

My monitor is the LG 38BN95C-W

 

[andrei524]

I also have the LG 38WN95C and have the same exact issue.
I tested this using two M1 MacBook Pros from '21 (1 base model and the other with a slightly beefier chip and 32GB ram) and various Thunderbolt 3/4 and passive/active cables.
What's interesting is that it didn't happen all the time, at first it worked perfectly then slowly it started happening more and more often, to the point where now the monitor doesn't even turn on on thunderbolt. Also, it used to be just one of the laptops with which the monitor had issues, now it's both of them.
I bought the monitor off Amazon, and it seems they don't do any sort of servicing, they'll just give me my money back and that would allow me to purchase a new one (which at this time is more expensive and takes a couple of weeks to be delivered...)
I don't know at this point if this is an issue related to the monitor or it has something to do with the M1 chipset so I'm not sure if I should purchase this display again or go for a different one.

Edit: Also forgot to mention there was also another issue I had with the monitor, namely the screen would flicker at 144Hz given that more than x% of the image was a certain shade of grey. Weird right?
I work as a software engineer and use intellij idea based IDEs on a daily basis, and noticed with the default dark theme, if it covered more than around 70% of the screen, the display would exhibit this odd backlight flicker effect. Moreover, it sometimes showed windows, that were previously on the screen, appearing almost "burned in", pretty much seeing a faint image of a previous window.
This also happened on certain default MacOS apps in dark mode (however harder to reproduce). Turning the refresh-rate down to 120Hz and brightness below 60% + tinkering with the Gama seemed to fix the issue temporarily. This also happened on both of my M1 macs, however I haven't tested this with a different machine unfortunately.

 

[andrei524]

Since my last post I have had LG repair my monitor — they changed the monitor board.
A few months have passed since the repair and everything is still working fine!

 

[jaredly2]

I'm using an LG-38WN95C with my M1 MacBook Pro, and it was working great until the 13.5.1 (22G90) update. Now, the monitor won't connect with USB-C.

Solution: After the update, the USB-C connection couldn't handle both charging and the monitor signal. But I found a workaround:

1. Keep the USB-C plugged in.
2. Add the MagSafe charger.
3. Now, the monitor works over USB-C again.

Note: Removing the MagSafe charger will stop the monitor from working over USB-C.

Hope this helps someone out there!