No Signal with usbc/dsp adapter and MacBook Pro 2017 with AOC U2868PQU monitor after a couple of weeks

I have had been using an AOC U2868PQU monitor for over 2 years with a Windows Lenovo Thinkpad via Mini DisplayPort to DisplayPort adaptor successfully. In September 2017, I switched to a MacBook Pro (15-inch, 2017), which only contain usb-c ports. I purchased the Plugable USB-C to DisplayPort adaptor in September of 2017 thru Amazon. It worked flawlessly with no issues, for a couple of weeks. Then unexpectedly it stopped working – No signal. Monitor does not recognize a connection. MacBook does not recognize a connection. After a few weeks after responding via Amazon, eventually plugable technologies sent me a replacement cable. Monitor recognized the input immediately and I was up and running happily again. Then again a couple of weeks later – no signal.

I have combed through the support forums on apple and here on pluggable. I tried the following:

All attempts have not helped resolve the issue.

Is there anything else I can try to remedy the situation?

Hello Leo, thanks for posting and I am sorry to hear that the replacement cable stopped working, as well. Based off of the steps you’ve already tried, it could be that another cable became faulty (which is extremely rare).

Just to clarify, does the same behavior occur regardless of USB-C port you are connecting to and rebooting the system has not helped, either?

One additional thing to check on the monitor’s end would be to change would be the DP mode that the ports are set to within the monitor’s on screen menu. Does changing the DP mode to DP 1.1 help, if applicable (as illustrated on page 27 of the manual here –>…) ?

Thank you,

David W.
Plugable Technologies

Hello David,

Thank you for your reply!

To your first question - yes, the same behavior occurs regardless of USB-C port I connect to. And yes, I had rebooted. Or do you mean the sequence of changing ports AND rebooting system immediately after? I had not tried that.

Anyway, to your second suggestion - changing of the DP mode must have done something, because the second monitor is now working!!!

Unfortunately, I can’t say exactly the sequence of what made it work. Because there was no signal, I could not bring up the monitor’s on screen menu. So to get around that I connected another device (my raspberry pi) to the monitor, via a straight HDMI-to-HDMI cable, since that is the only output available with the raspberry pi. Once I had the display come up via HDMI, I was then able to bring up the monitor’s on screen menu, navigated to the DP mode setting and changed it to 1.1.

I then unplugged the HDMI cable and plugged in the usbc/DisplayPort adaptor from the macBook. Either the monitor automatically detected and switched to the DP input or I manually switched the monitor to the DP input. The screen went blank and remained blank. However, instead of eventually the monitor displaying the “No Signal” message, it just remained like a black screen and I noticed a hard to see but slight flicker to a slightly lighter shad of black. I launched “About This Mac” window and clicked on the “Displays” tab. It showed the U2868 Display. That was promising to see! However, still no picture, but no “No Signal” message either.

I decided to try to switch the DP mode back to 1.2. To do this I had to plug the HDMI cable back to my raspberry pi again, since I could not bring the monitor’s onscreen menu up again in it’s current state. The monitor did not automatically detect and switch to the HDMI input and could not toggle to it manually, so I unplugged the usbc/DP adapter cable and powered down the monitor off then on again. The HDMI input was detected and got picture. I was able to get to the onscreen menu and set the DP mode setting back to 1.2. I then reconnected the DP adaptor cable. The extended macOS desktop now appears on the second monitor!

I unplugged HDMI cable from the other device and the second monitor connection appears to continue to work!

Post-mortem thought: I wonder if all I needed to do after changing the DP mode setting initially was just to power off and on the monitor again.

So I am back to having my second monitor fully functioning again in DP mode 1.2 as originally set, with the usbc/dsp adaptor cable.

Perhaps you may have any idea of what and why the DP setting switch to 1.1 caused the monitor to be “detected” somewhat and why it is operating again after switching it back DP mode to 1.2?

My gut tells me that this may happen again, but at least I know what to try to do if it does!

Thanks David!

So wanted to provide additional updates after the weekend. On Friday, my end of work day, as what I usually do everyday, I walk away from my MacBook Pro, leaving it to go to sleep. When I returned to it this morning (Monday), the display was gone again and was no longer recognized by the MacBook. I went through what I did last time, to toggle DP mode back and forth, unplugged usbc/dp adapter cable from the MacBook and then turned the monitor off and on. Got the display back.

If this condition reappears again tomorrow, I will try turn off/on the monitor to see if that will do anything (although, I remember doing this numerous times in the past with no success). If that does not work, I will switch and keep the DP mode set to 1.1.

I will continue to monitor and report back any changes in behavior, in the hopes to get feedback to attain a consistent behavior where the display monitor retains its connection to the MackBook.

Hi Leo, thanks for the replies and apologies for my delayed response.

Thank you so much for the documenting and letting us know the steps taken to fix the issue whenever it does arrive. I am unsure why it is happening. One thing to further narrow things down would be to test with another monitor, but understood if that is not a possible test.

Otherwise, there’s not much else we can suggest other than trying another pre-tested replacement USBC-DP cable. If interested, please just let us know and we can begin this process.

Thank you,

David W.
Plugable Technologies