Unpredictable behavior with Dell Ultrasharp U2415 Dual Monitors

Question

Ever since I set up my two Dell U2415 monitors, I've had sporadic problems with one or both of them not being recognized. I have a Windows 10 T1700 Dell Precision system with dual monitors. This is the first time I've ever owned monitors that utilize the Mini DisplayPort technology. The problems are:

1. I would like to turn the monitor power OFF at the end of the day, because I don't like the glow of the light from the power buttons when not in use. But it seems turning off the monitors always brings problems when I come back to the computer the next day. For instance, if I turn off the monitors, the next time I turn everything back on, only 1 monitor is recognized. Sometimes it's the one on the right, and sometimes it's the one on the left. The other monitor has power, but no input is recognized, and it just says "Entering Sleep Mode" or something like that, and there is no display. When this happens, there is no 2nd monitor available when I go into Control Panel display settings. It's as though the monitor is not plugged in. I have to restart my PC again (this time, making sure both monitors are turned on at the time that it restarts), which sometimes seems to get both monitors back.

2. On Monday I got alerted about a Dell Display Manager software update, so I installed the update. At the end of the day, I put my PC to sleep (leaving monitor power ON). When I came back in the morning, the PC woke up only recognizing 1 monitor. I had to go into Windows 10 Display Settings and extend it to the 2nd monitor (why am I having to do this again)?

Why are these things so touchy? Is there a precise order in which everything must be turned off and back on so that both monitors will be properly recognized? Should I wait until my PC is powered off to turn the monitors off? Do I have to turn on the PC BEFORE the monitors (or the other way around)? Do I need to turn on the primary monitor BEFORE the secondary monitor (or vice versa)? There does seem to be some magic to all this, and I would like to understand exactly what is going on. I want to be able to turn off the monitors whenever I like and feel confident that both will be recognized when I turn them back on. At this point, I am leaving the monitor power on all the time due to the many problems I've had and because I simply don't trust them.

Thanks

DELL-Chris M · Accepted Answer

For the computer to identify a monitors DP/mDP, the monitors need to be on first, then the computer video card reaches out to the monitors DP/mDP to initiate the handshake. Any change in that order will disrupt the handshake. A computers hibernate or sleep modes tends to confuse the DP/mDP handshake. So I do not use them at all.

DELL-Chris M · Answer

I would start with this scenario -

The computer and both U2415's are on and you are in windows.

End of work day =
* Turn the computer off, Click Start- Shutdown- Shutdown- Ok or Click Start- Turn Off Computer- Turn Off
* Turn both U2415's off via their power buttons
Next day =
* Turn both U2415's on
* Turn the computer on

In this scenario, how do all three operate together?

kewpcg · Answer

Thanks Chris. Tried this and it seemed to work out okay. Just because I like to understand these things, can you explain a little about the mDP technology and why they need to be turned off last and started first (before the PC)? I didn't see it mentioned anywhere in the monitor documentation, and have never had such a struggle with monitors. I'm beginning to wonder if these problems are unique to my particular setup, or is this common with the mDP dual monitor scenario?

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Unpredictable behavior with Dell Ultrasharp U2415 Dual Monitors

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