Mine is one of the very earliest launch units from back when it first launched, and it's always been a bit twitchy (used together with an early 2011 13" MBP.) Every once in a blue moon it would just simply disappear completely (not literally, obviously, heh.) It'd go black, my attached keyboard would stop working, and it would not list under Displays in the system settings applet or in "About my Mac" under Thunderbolt heading. Sometimes the Mac would hard-crash when that happened, forcing me to do a cold reboot. Often it would not wake up from sleep after a random, X number of wake/sleep cycles - "X" sometimes equalling 1, sometimes 20+. If I wanted to continue using it, I had to re-plug the TB cable, then restart the MBP, and then it'd function normally for another number of wake/sleeps. Unless I restarted my Mac I would have to keep re-plugging the cable every time I needed to use it, and although this got kind of tedious I figured, first world problem, and kept waiting for a software patch to arrive which would clear these problems up, which never happened. Not even the latest patch which arrived a couple months ago changed anything. ...Which brings us to present day. I was using my Mac, I went away for a while and when I came back the display had blacked out. Opening the lid did nothing (Mac was completely unresponsive), so I held the power button until the computer shut off, then turned it back on. TBD did not work afterwards, so I did the usual song-and-dance with re-plugging it, pulling its power cord from the wall socket (dust bunnies! Lol), and so on. Nothing changed, the TBD was still black, and did not show up in the OS. Holding my hand on the TB connector I could feel it was warm - and it is STILL warm now even with the computer sleeping - but the display just isn't there, so to speak. I've had it serviced once just before my Mac's applecare ran out this spring, but the service tech claimed he could find nothing wrong with either my Mac or TBD, so I shrugged and just continued using it like I've been doing all this time. Anyone know if there's anything to be done to maybe coax it back to life, or should I return it to the repair center and let the techs there have another crack at it (paying through my nose for the pleasure this time no doubt)? TYVM for any assistance... Edit: Oh and by the way... The TBD's power supply seems fine, because my Mac charges/runs just fine off of the integrated magsafe connector. Can't charge my iPhone off of the USB ports on the unit though.