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LG Ultrafine 27MD5KA-B provides power to laptop, but does not get detected by computer. No video.

intothewild

Apr 18, 2020
2
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Apr 18, 2020
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Hi all! First time posting here. I'm a software developer that has worked with laptop repair in the past, but I am not seasoned in hardware. Seeking help on the following:

I have a LG Ultrafine 27" 5K 27MD5KA-B monitor that I have acquired. When I first hooked it up, my laptop would detect it and display video, but it would intermittently disconnect/reconnect every couple of minutes. It's only connection is a Thunderbolt 3 / USB-C connection, so at first I used the cable that was provided. My next step was to try a brand new Thunderbolt 3 cable directly from Apple. The display issues persisted until one time the video went out it it has never been able to be detected on the computer again.

I've tried all of the unplugging the power from the monitor, trying different ports on my Macbook Pro to connect to, resetting the PRAM/SMC on the macbook, switching thunderbolt 3 cables, etc, but to no avail.

My next step was opening up the monitor, since this monitor was out of warranty and I wanted to see if there was anything obvious inside that could be causing the issue. I've attached photos of the only two main circuit boards that are in the monitor. One appears to be the main board that has the ports attached to in and connects to the LCD cable. The other appears to be the power board. I couldn't notice any bulging capacitors or odd burns anywhere on the boards. There was a small button on the main board that was only accessible when the back case was removed. I pushed this button while the monitor was plugged in and it actually displayed a rotating image of color blocks to the screen (Red, Green, Blue, etc). This showed me that there was actually power to the display in some way. I'm assuming this is used at the factory to test the display for dead pixels and such.

One thing to note is that the USB-C port that connects the monitor to the computer is a bit loose. This seems to be a complaint for this model of monitor and people who have complained about the "wiggle-room" of the port usually seem to not have display issues. I'm not sure though.

Has anyone run into an issue like this or does anyone have a suggestion on what to try next?

Thanks!

Images of boards and monitor label:

https://ibb.co/d7Xtf3R
https://ibb.co/BysStgt
https://ibb.co/yPFDvHj
https://ibb.co/G7chnM3
 

Cirkit

Oct 28, 2015
148
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Oct 28, 2015
Messages
148
One thing to note is that the USB-C port that connects the monitor to the computer is a bit loose.

I would suspect this. Are you able to provide a detailed close up photo of the solder connections on the reverse of the connector?
 
Last edited:

greens

Apr 26, 2020
1
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Apr 26, 2020
Messages
1
I have the exact same problem, except I'm using a MacBook Air. I think the difficulty is in the power supply, not the video connection, but I'm not sure. Any help would be welcome.
 

MainMacMan

Jul 28, 2020
2
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Jul 28, 2020
Messages
2
Any Update here? I am experiencing the exact same problem. any help appreciated
 

thebumpershoot

Jun 21, 2021
2
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Jun 21, 2021
Messages
2
Hi there, I know this is a while back but i just got given 3 of these monitors all with the same issue, they all have the button on the back that makes them display the Red Green Blue Black White loop, and they all chrage the macbook pro but none of them come to life, any thoughts?
 

intothewild

Apr 18, 2020
2
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Apr 18, 2020
Messages
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I've given up on fixing mine, but I believe the issue has something to do with a bad / loose chip connection on the main logic board. As you've stated, the power to the Mac is fine and the RGB test loop is fine. Good luck!
 

MainMacMan

Jul 28, 2020
2
Joined
Jul 28, 2020
Messages
2
Hi there, I know this is a while back but i just got given 3 of these monitors all with the same issue, they all have the button on the back that makes them display the Red Green Blue Black White loop, and they all chrage the macbook pro but none of them come to life, any thoughts?

Good day, I spent WAY too much time on this problem. The TBT3 Female connector on the monitor needed to be replaced - I believe this board is separate or connected to the Logic board. I believe the total to replace out of warranty board was about 550.00. I had to search for an AUTHORIZED LG repair place as these boards are not available to 3rd party repair firms. They must order the board from LG - Very appleish :(
 

thebumpershoot

Jun 21, 2021
2
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Jun 21, 2021
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Hey thats some really useful info thanks, saved me lots of time. Thanks for your help everyone!
 

derwoodums

Jan 25, 2023
1
Joined
Jan 25, 2023
Messages
1
Do yourself a favor and try a new Thunderbolt cable first. Not just a USB-C cable, it has to be a Thunderbolt 3 cable with data transfer rates of 40 Gb/s and 100 W Power Delivery. I had 2 of these displays apparently go dead within 2 months of each other. I chased my tail and wasted a lot of money replacing the logic board and the power supply board and still no joy. Finally I saw a post that the Thunderbolt cables can go bad over time (plugging/unplugging, moving, ...). I bought one (they're about $50), put all the original cards back in the display, and both are now working. I'm not saying the main logic board can't go bad, just try the easy fix first!
 
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