U2415 blanking randomly, 15' cable, MBP

Several unknowns here. First, we only tested/validated on Windows operating systems =

Second, Dell has only tested/validated 6' cables which is what we provided. If the Dell 6' cable never has the issue, then that is your answer. The MacBook Pro is not sending a consistent signal through the 15' cables causing the U2415 to lose the signal. You should ping the Apple users on their Forum and see if they can offer some insight.

We just replaced 1/4 of our company with these monitors. Our setups use 4 monitors per desk. This is important because the blinking you refer to is loss of signal. So when one monitor loses signal, then all those windows that a user spent time setting up get rearranged in random way. In some cases the monitor signal does not come back up and monitor appears dead. I cannot  express the loss of face my team experienced in what should have been a positive experience for both user and the tech team. We spent hours responding to my monitors are blinking and my windows get rearranged or my monitor has gone out. Eventually after many days our fix was to buy display port cables and use those. I am not going to do work for Dell troubleshooting but let me be clear at what we believe is the case. Either the mini display ports on monitors are bad, or the mini display port cables provided with monitor are bad, or both.

This issue is applies to all monitors we ordered, and we ordered them in stages, so not like we just got unlucky with a bad batch. Let this also be a record that states that these monitors are bad out of the box.  

My answer to you is to use Display Port and not mini Display Port. Nothing you can do to fix it as this is hardware issue on the monitor and you got it like that from Dell.

Rough situation and interesting conclusion. Unfortunately, at least in my case it has to be something more. The mini displayport on my monitor was never used, only the fullsized DP. My laptop output is mDP (via Thunderbolt port) to which I used a mDP to DP cable. In fact I tried 3. I have also tried a mDP to HDMI in a 10ft run (had one laying around), and while more stable than the previous 15ft mDP/DP cables mentioned, still cuts out the monitor. Since I am not pushing any crazy resolutions or daisy chaining monitors my last resort is to use a 15ft HDMI Redmere cable. I'm hoping the extra oomph in the Redmere chip equalizes any issues over the 15ft run the Displayport spec doesn't seem to support. I'm curious were the cables in your set up standard 6ft runs? It's my understanding mDP is electrically the same as DP so if it's a bad port it has to be a manufacturing problem instead of a spec issue...

Chris, I gave up on the displayport over cable runs longer than it's spec'd for. I went for a 15ft HDMI cable with a Redmere chip. There is no way there should be any issues over this short distance with a chipped cable and even when writing this post, my U2415 blanked out for like two seconds before coming back up. The only common denominator now is this monitor. What gives? I'm starting to look for an alternative if I can't get this to work reliably.

-Michael

Per the warranty, you may initiate a monitor exchange. Test the replacement before sending any monitor back to Dell. If the replacement does not have the issue, keep it and send us the original. If the replacement has the same issue, two monitors could not be at fault. Send the replacement back to Dell. Look to something else in the mix as the culprit.