Dell P2715Q Display with iMac

I have an iMac (Retina 5K, 27-inch, Late 2014) running Mac OS 10.12.6 with a second display attached - Dell Ultra HD 4k Monitor P2715Q 27-Inch Screen LED-Lit Monitor.

Everything is good but every once in a while the iMac does not wake properly and I have to do a hard reboot. The Dell screen goes to sleep and the iMac screen stays black.

The display is connected with a Cable Matters Gold Plated Mini DisplayPort (Thunderbolt Port Compatible) to DisplayPort Cable, Black, 6 Feet.

I’m pretty sure that the problem is related to some sort of handshaking (detect displays) between the Dell and the iMac.

I have tried just about everything included a reinstall of the OS, but I still find myself having to reboot the Mac every day or two.

Besides this one headache, the monitor is great - but if I have to, I may just purchase another secondary display. Anybody else encounter this? Are there any suggestions for fixes or for a display that is more compatible?

only idea to isolate the source of the problem: try with another displayport monitor …
did it work previously ?
can you try with another monitor, not eventually display port ?

[quote=346421:@Jean-Yves Pochez]only idea to isolate the source of the problem: try with another displayport monitor …
did it work previously ? [/quote]
Unfortunately, I don’t have another display.

I am about to get a 2017 27" 5k iMac, and just ordered two adapters from Cable Matters (not the same as the OP, as I will have T3 ports not T2)… And will be using them to connect two Dell 1905FP monitors (which are only 1280x1024)… so I sure hope they work

The monitor I have is great except for that occasional reboot.

Have you tried to Power ON the external Monitor after the iMac Boot is over ?

I have no problems during boot, only after waking from a deep sleep.
If I set the iMac not to sleep, or turn off the external display before the iMac goes to sleep, the problem seems to be avoided.
Unfortunately, this problem is intermittent. For the most part, the iMac wakes with the two displays OK - but then there is that one time, usually when I need to access the iMac remotely, that the crash occurs.

I get this problem occasionally with a Apple TBD and a MacBook Pro; without the display attached the MacBook Pro will wake correctly; with it connected theres always the chance that the machine won’t wake up properly (Kernel Panics galore).

I also have this problem running a MacBook Pro and an LG 34inch widescreen monitor. It hasn’t happened recently but used to occur about once a week. Very strange!

Same here with a Dell monitor. Happened both for my old MacPro and the new Hackintosh. The monitor now isn’t allowed to sleep.

exchange your monitor temporarly with friend or work, if you kindly ask no one can refuse.

You don’t know Americans very well do you? :smiley:

Does anybody know of a monitor that works well? I may just buy it and see how things work. Staples, for example, has a 14-day return policy - so I can return it if the same this happens.

Exactly the same problem with that monitor but with a HP EliteBook 840.
Windows 10 doesn’t recognize the monitor when waking from sleep and I have had to disable sleep entirely. Connected using DisplayPort directly from the laptop. Doesn’t happen when using HDMI but then I only get 30Hz refresh rate. With DP I get 60 Hz.

Philips Brilliance B-line 26’’ USB-C
ref 258B6QUEB/00
has all connectors you can dream of, from vga to usb-c direct connexion.

Are-you able to see a difference between the two refresh modes ?

I have a Dell UP3214Q, it has a similar issues, no signal when bringing the screen out of power saving, sometimes half a panel when turning on. I sold my trashcan a while back and went back to windows so my computer doesn’t suffer from not turning on any more. My bro’s monitor does the same, I think Dell dropped the ball on this chipset. They claimed to have fixed it in a new firmware (which I have) but it hasn’t. I can live with it, happens maybe once a week.

Between 30Hz and 60Hz? When I mis-configure my monitor and put it into 30Hz its like night and day, I can tell the different with just the mouse refresh speed, let alone window movement refresh speed.

Oh yes - dragging windows and moving the mouse clearly shows the difference.

The pain is that I need to reboot the system since the display scaling on Windows sucks and force me to reboot to be restored when the monitor took a too long nap. The hassle or shutting down virtualbox and restarting everything is a PITA.

Investigating further, I have found that the Dell UltraSharp U2515H in my home-office seems to be compatible with my laptop and sleep. It was bought just a couple of months ago, but since the monitor in my office doesn’t work reliably I haven’t bothered testing it on my home-office monitor until now.
@JulianS - do you know how to check the firmware?