Strange MacBook Pro, LG monitor connectivity issue

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Level 1

42 points

Strange MacBook Pro, LG monitor connectivity issue

New MBP 14". Ran into a weird connectivity issue with my LG 32UN880-B monitor. I have the monitor attached using the USB-C to USB-C cable that came with it. It worked just fine on my M1 MacBook Air. But not so much with the new MBP.

If the MBP is already booted up, it connects to the LG monitor fine. However, if I reboot the MBP with the monitor connected, it does not connect. Pulling the USB-C cable and reconnecting does not work; still no connection. And it's not just video that doesn't work. The LG 32UN880-B is capable of powering the MacBook. But the battery icon does not register that it has power in this reboot use-case. The only way I can get it to connect is to power the monitor off and then turn it back on. Or, I can pull the USB-C cable to disconnect the monitor before I reboot, then reboot the MBP and then reconnect the monitor after I get past the password screen.

I ended up on a call with second-level Apple support. We tried everything. We tried different USB-C cables. We reset everything. No luck.

Then they asked me to try a different connection. I had a DisplayPort to USB-C cable sitting nearby. And as soon as I switched to the DP cable, the monitor worked fine again. It finds it after a reboot every time using the DP cable. But fails every time with the straight USB-C cable.

I got off the call with Apple feeling like it was an LG issue. But thinking about it more, I'm not so sure. It worked fine with my previous MB Air. A few differences - the Air had an M1 where my MBP has an M1 Pro. I had Big Sur on the Air - obviously Monterey on the MBP. But I sold the Air in order to get the Pro so I can't go back and test the Air any more.

I feel like there's something funky with the way the MBP or Monterey is handling the USB-C ports during boot-up.

Any thoughts or suggestions?

MacBook Pro 14″, macOS 12.0

Posted on Oct 28, 2021 9:27 AM

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Answer 1

maxfill

Level 1

8 points

Jan 25, 2022 1:15 PM in response to EdMartin

I believe the issue is the power output of the LG monitor is only 60W and the needed power for the new MBPs (14" and 16" M1 Pro) needs to be at least 67W. I don't have anything foundational to back that theory up, but that is where I have landed.

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Answer 2

Dec 18, 2021 6:15 AM in response to Lucasnygaard

any changes after Monterey 12.1 update, released Monday, 13-Dec-2021?

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Answer 3

ubbulls

Level 1

8 points

Nov 6, 2021 7:23 AM in response to EdMartin

I'm having the exact same issue with the new MBP 14" and the LG 32UN880-B monitor. The only way I'm able to get it reconnect with the monitor is pulling the power supply off of the monitor and then reattaching it. Were you able to figure out any other solutions?

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Answer 4

Argelius

Level 2

257 points

Jan 17, 2022 1:25 PM in response to EdMartin

I have been using the LG 5K Superfine monitor in clamshell mode with my 14" M1 pro MBP ever since I got it (the MBP) without problems. They are connected with the USB-C to USB-C cable that came with the monitor.

Then, one day (with no system changes/updates I am aware of), the external monitor stopped being recognized by the MBP, although the USB'-C cable is still supplying power to the MBP.

I tried all of the above things (different cables, power cycling, different USB-C ports, etc).

So I thought maybe the monitor was bad, so I bought a different one from Samsung also with a powered USB-C. It worked, so figured it was the LG. Then after one day, I plugged the monitor back into the MBP and same thing -- monitor not recognized by the Mac as being attached.

Also, on the Samsung I connected the MBP to it via HDMI and this worked fine.

So this is definitely a problem on the Mac side, specifically with the USB-C ports.

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Answer 5

Dec 18, 2021 7:45 AM in response to Lucasnygaard

12.0.1 is not the same as 12.1 released Monday, 13-Dec-2021.

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Answer 6

Nov 6, 2021 7:31 AM in response to ubbulls

You have 90 days free telephone support with the purchase of a new Mac. Call them. Have your serial number at the ready.

The more instances of this problem they see, the sooner it will get fixed.

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Answer 7

ubbulls

Level 1

8 points

Nov 6, 2021 7:39 AM in response to Grant Bennet-Alder

Thanks, will do!

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Answer 8

jmw00d

Level 1

8 points

Dec 7, 2021 2:38 AM in response to EdMartin

I've just bought this same monitor to use with my new MBP 16" and it's doing the same thing. Thought I'd got a dud screen or I was going crazy. Will also try and call Apple!

Thanks

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