Macbook Pro 16 Thunderbolt ports dead/damaged twice after used with Samsung CJ89 43" monitor with USB-C

Question

I have a brand new 2019 MBP and I hooked it to a Samsung CJ89 43" monitor directly through USB-C. It worked for a while and then suddenly the built-in screen started flashing and then the connection to the monitor was lost. The laptop reboot itself and now all 4 of the thunderbolt ports are not charging anymore. What's worse is all above happened last week. So I took it to Apple store and got it repaired. Basically they replaced the logic board and Touch ID on the device.

Now, I plugged the replaired MBP to my monitor with the same USB-C cable which is the original one from Samsung come with the monitor. It worked for a while. But the nightmare happened again suddenly. I can hear the fan go wild and it alerted with message "USB ports disabled, unplug ...". All the 4 ports are not charging AGAIN!

I tried everything like reset SMC and NVRAM etc, none of them working. Very frustrated at the moment. I'm not sure where the problem is and how can I solve this? I booked in another Genius Bar appointment on Tuesday. However, the thing is, even if it's replaced or repaired - again, I really can't tell what is causing the issue and I'm afraid of plugging it to the USB-C port on my Samsung monitor after that.

Need some help and advice please.

Answer 1

I know you’re frustration and you’re hoping against hope that it’s something simple, but the evidence is pointing to a defective monitor. Apple may decline warranty service for this second repair if plugging into the same monitor causes the same issue.

I answered a very related question regarding monitors and warranties.

Is it safe to connect external screen to MacBook via USB-C from the warranty perspective

In short, you should feel confident that plugging in your monitor, especially a known brand like Samsung is a safe procedure. However, if it’s found that the monitor is what is the cause, they may direct you to Samsung to cover the repair costs - and would legally be within their rights to do so. Samsung isn’t perfect, nor is Apple and it’s not unreasonable that Apple decline something that‘s not their fault.

I’m not a lawyer and this should not be construed as legal advice, just my opinion based on many years of this type of experience.

Bottom line is you may get it repaired or you may not. But, if you do, before plugging it in for a 3rd time, it would be in your best interest to not plug you Mac into that monitor until you get it checked out.

In fact, as a DYI test, you can try a USB-C meter inline with another device (like a sacrificial Android tablet) and see what your power is being sent by the monitor. Anything cheap and you don’t mind losing. Anything but your Mac. If you see more than 20V @ 5A and/or you fry the test device means you’ve definitely got a problem with your monitor.

It’s highly unlikely Apple will fix this a third time