Why does my external 23.7in LG 24MD4KL display go brownish on my MacBook Pro 16in when waking?

Question

Why does my external 23.7in LG 24MD4KL display go brownish on my MacBook Pro 16in when waking?

Quite often, but not always, when my MBP wakes from sleep or leaves the screen saver, the LG screen is brownish and the resolution seems smoothed. (My MBP screen is does not change.) I can use the LG screen but it looks horrible. A refresh of the display returns it to normal view. Such as changing resolution via display preferences or hitting escape from login and try again. The AMD Radeon Pro 5500M graphics card has 8GB of memory. Any ideas on why this happens and how to fix it? But before you offer suggestions, these are a few of the things that I have done.

1. Reinstalled OS 10.15.2 in recovery mode

2. Reset SMC and NVRAM

3. Ran Disk First Aid

4. Ran Apple Hardware test (no issues)

5. Got a replacement monitor from Apple. LG said they did not have this issue logged.

6. Tried connecting LG with either Thunderbolt 3 or USB C cables. No difference.

7. Set either MBP and the LG as primary screen. No difference.

8. Tried MBP keyboard, wired USB keyboard and Apple Bluetooth keyboard. No difference.

9. Tried waking only with track pad. No difference.

10. Connected to my old MBP late 2013. Seemed just fine.

I have noticed that occasionally the MBP screen will throw up some random lines about 2/3 of the way up the screen before the LG goes brown.

I am open to suggestions. Could it be a known driver problem? That might be the easiest fix (for me).

Posted on Dec 22, 2019 5:28 AM

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Answer 1

Dec 27, 2019 3:33 AM in response to William Hakes

For what this is worth and if anyone has this issue:

Since then:

I installed the 24MD4KL on an MBP late 2013 and it functioned perfectly. I installed my old 22MD4KA on my MBP 16in and when the screen turned off, it did not restart until I restarted my computer. Even unplugging did not help.

Safe boot. Could start screen saver but when it woke from sleep, it was fine.

Set up a new account: Same problem with LG screen. But then I hit the return key, both screens were dark. I turned the room ights on and the MBP screen brightened whilst the LG didn’t. Turned off True Tone and seems to have fixed LG screen.

Rebooted from regular account: With True Tone turned on, only LG display is dark. Turned of True Tone and turned on screen saver and waited for screen to shut off, LG display did not darken.

This is a work around. Either there is an incompatibility with the LG driver or there is a bug in 10.15.2. Or there could a flaw in the light sensor in the LG display. But since this is my second display, I kind of doubt it. But it could be. Or maybe I don't understand. Case closed.

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Why does my external 23.7in LG 24MD4KL display go brownish on my MacBook Pro 16in when waking?

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