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Released in July 2018, the 15" MacBook Pro, model A1990, features a 15.4 inch LED-Backlight display with True Tone technology, TouchID, and up to 6 Core i9 Processor.

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USB C Dead, USB Accessories Disabled.

Hi, my 15” MacBook Pro 2018 Touch Bar system has a problem

One of the 4 USB C's has failed! I did an update to Catalina it was not fixed. I have tried I believe correctly resetting NVRAM / SMC but no success... The system passed the diagnostic test. I have tried safe boot again nothing.

When I try to plug in something it pops this message (in Mojave I have never received a pop like this)

Block Image

USB Accessories Disabled

Unplug the accessory using too much power to re-enable USB devices

After some experimentation.

Connect first to the Dell monitor, cable -> charges. Then I connect also the Apple charger to the problematic USB C port it charges.

I unplug the Dell monitor cable, then it charges from the problematic USB C port (but I’m not sure if it works the percentage drops, but if I unplug it the display dims down…)

I tried while plugged in and powered the hunt to SMC reset but I failed.

Somehow I believe that something with electric circuits, electricity from my Displays USB C charge has been evolved in this case. My display is a Dell 3219Q USB C.

Any ideas what to try?

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I think you are right your Dell display is a factor here. Your Dell display is designed to be a power source for your system as well as being a display. But you appear to have been trying to also charge your system using the Apple charger in addition to the Dell display so you have two chargers connected!

The USB-C standard has a weakness which you appear to have fallen into! It currently doesn’t over dual power supply support.

I had two systems come into me which exhibited this issue. In there case they where using two chargers as the system, was being used to render videos. The owners thought they could run the systems with two chargers as the system would run out of power between the battery and the one charger with some long videos! Sadly, they damaged their systems TB/USB-C ports. I suspect you’ve done the same here.

The onboard diagnostics have limitations it won’t test the power services as it has no means to do that. You’ll need a USB-C power meter to test your ports ability to receive power as well as deliver it.

Here’s one unit that will do the job USB-C Tester DC Digital Amp & Volt meter

But you still have to deal with your damaged logic board. If you still have AppleCare coverage or have gotten AppleCare + service support contract you should be able to get Apple to fix your system, If not there are people who can replace the damaged power control chip or just not use that set of ports.

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so a its a chip damage or I have to replace the USB C ports with the specific replacement

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Sadly its not the port connector assembly its the logic on the logic board the connector connects to. There is a bit of logic which is designed to monitor the power entering the system as well as power leaving. It was not designed to handle doing both at the same time! Which causes the damage.


If i dont fix it is there any chance to destroy the whole logic board? I dont mind the 1 usb c!


I would get the USB-C meter to make sure of things. Loosing one port won't be a big loss but over time you could loose its mate.


The fact is that I have never charged the macbook, with a double charge.

This was just an experiment after the USB C failed....

The paradox is I believe the display did the damage to it... Because at the moment I discovered that the one of the USB Cs failed was at the same time the dells USB C cable died. I cant recall before this event if it was working or not..


Without having a means to test the USB-C ports in-line with the displays power it will be hard to tell what the cause was/is.

I do recommend getting a good surge suppressor or better yet! A UPS.Making sure all of the systems peripheral's are all connected to the same surge /UPS unit.

You still should check your outlets making sure they are correctly wired and the sound connections are properly done at the outlet and at the main breaker panel to the building ground point which is either a cold water pipe leaving the building or one or more ground rods. Making sure the connection is clean and secure.


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