Retina iMac screen flickering with Dell 4K secondary display

[boogi]

I've been using my Retina iMac (base model 3.5ghz i5 with M290x) with a Dell 27" U2713HM as a secondary display and things were fine. I recently upgraded to a Dell 27" P2715Q 4K display and noticed some graphical quirks on my system. My friend has the same exact setup (base Retina iMac and P2715Q) and hasn't noticed these issues. Unfortunately, he doesn't live nearby, so we can't test all our hardware at once. I've been pulling my hair out trying to troubleshoot, so I thought I'd post here to see if anyone has any suggestions. I'm trying to figure out if there's something wrong with my iMac or the Dell display (or possibly the cables?).

For the record, I've already tried resetting the SMC and PRAM, and I also did a clean install of Yosemite, and none of those fixed the issue.

I have tried three different Mini DisplayPort to DisplayPort cables. All of them are DisplayPort 1.2:

1) Cable that came with my Dell monitor -- the iMac recognizes that a secondary display is connected in System Prefs -> Displays, but the Dell monitor remains black and no image ever appears. I've tried toggling the "Mirror Displays" box, which I've found to help in the past, but that didn't work either.

Surprisingly, I tested this cable and the 4K display with my girlfriend's MacBook Air, and it worked fine. I also tested this cable with my iMac and my old Dell monitor, and that also worked.

2) 3' StarTech cable from Amazon -- the 4K display works fine with this cable, but when I wake my computer/displays from sleep after 5+ minutes (<5 minutes seems fine), the iMac screen will flicker to black twice while the Dell monitor tries to wake. The Dell monitor will then show a light blue color until I login. After I login, the Dell monitor works fine again.

Here's a video of what it looks like. (iMac on the left and Dell 4K display on the right. In this video, the iMac background actually switches to a solid gray after the second flicker instead of the frosted desktop background of the login screen, which I've never seen before.)

3) 6' StarTech cable from Amazon -- same results as the 3' cable (scenario 2).

Has anyone else seen anything like this? I would really like to figure out if there's a problem with my Dell 4K display or my Retina iMac. I'm willing to try out any other testing scenarios as well. Thanks in advance!

 

[phpmaven]

I've been using my Retina iMac (base model 3.5ghz i5 with M290x) with a Dell 27" U2713HM as a secondary display and things were fine. I recently upgraded to a Dell 27" P2715Q 4K display and noticed some graphical quirks on my system. My friend has the same exact setup (base Retina iMac and P2715Q) and hasn't noticed these issues. Unfortunately, he doesn't live nearby, so we can't test all our hardware at once. I've been pulling my hair out trying to troubleshoot, so I thought I'd post here to see if anyone has any suggestions. I'm trying to figure out if there's something wrong with my iMac or the Dell display (or possibly the cables?).

For the record, I've already tried resetting the SMC and PRAM, and I also did a clean install of Yosemite, and none of those fixed the issue.

I have tried three different Mini DisplayPort to DisplayPort cables. All of them are DisplayPort 1.2:

1) Cable that came with my Dell monitor -- the iMac recognizes that a secondary display is connected in System Prefs -> Displays, but the Dell monitor remains black and no image ever appears. I've tried toggling the "Mirror Displays" box, which I've found to help in the past, but that didn't work either.

Surprisingly, I tested this cable and the 4K display with my girlfriend's MacBook Air, and it worked fine. I also tested this cable with my iMac and my old Dell monitor, and that also worked.

2) 3' StarTech cable from Amazon -- the 4K display works fine with this cable, but when I wake my computer/displays from sleep after 5+ minutes (<5 minutes seems fine), the iMac screen will flicker to black twice while the Dell monitor tries to wake. The Dell monitor will then show a light blue color until I login. After I login, the Dell monitor works fine again.

Here's a video of what it looks like. (iMac on the left and Dell 4K display on the right. In this video, the iMac background actually switches to a solid gray after the second flicker instead of the frosted desktop background of the login screen, which I've never seen before.)

3) 6' StarTech cable from Amazon -- same results as the 3' cable (scenario 2).

Has anyone else seen anything like this? I would really like to figure out if there's a problem with my Dell 4K display or my Retina iMac. I'm willing to try out any other testing scenarios as well. Thanks in advance!

It seems like you've eliminated the cable being the issue. If it was me, I would return the monitor and get a new one and see if it has the same issues.

 

[WilliamG]

It seems like you've eliminated the cable being the issue. If it was me, I would return the monitor and get a new one and see if it has the same issues.

Be simpler to take the monitor to the Apple Store (maybe call and ask prior) and see if an in-store model does the same thing.

 

[dagamer34]

I know this thread is old but I just got the same monitor (Dell P2715Q) and it has the same flickering issue. I've recently used a Dell UP2414Q and it didn't have this issue.

 

[boogi]

I tried exchanging it to Dell and the second monitor had the same issue, so I think it's a software issue. I tried troubleshooting with Apple, and they said that it could just be that the monitor is too new that it isn't officially supported yet. I've kinda just learned to live with it. It really only affects the login screen when waking from sleep for me, although sometimes when I wake from sleep there is no image whatsoever on the Dell monitor (I've found that a reboot fixes the problem).

I know it's not an ideal solution (or even a solution at all), but I'm hopeful that it will go away over time. Let me know if you come up with a better solution!

 

[dagamer34]

Do you end up running yours at "looks like 2560x1440" mode or "best for display"?

 

[boogi]

I run it in 2560x1440.