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I have a MacBook Pro Retina, Early 2013, running Mountain Lion with an external monitor connected via a Thunderbolt-to-DVI adapter on the rear Thunderbolt port i.e. the monitor is connected to the Thunderbolt port closest to the power supply, the power supply also connected.

"On occasion" (once or twice a day), I don't touch the system for the sleep timeout period. The MBP's retina display sleeps. The external monitor stays alive without any content i.e. the galaxy desktop image is on, but nobodies home. What can cause the external monitor to remain on when MacBook Pro Retina goes to sleep? The external monitor should turn off with the Retina display when entering sleep mode.

This external monitor sleep problem happens about once or twice a day.

(My main concern is that I stuck my MBP in my backpack, took it out about 2 hours later, and the MBP was very hot and had shut itself down. Indeed, I booted it right away while it was still very hot to the touch so I could use SMC Fan Control to cool the unit down, and I noticed that my Hardware monitor software indicated that several of the internal core temp's were near 200dF. I have not been able to recreate this heating problem, but I have been able to recreate the monitor not sleeping problem, and I have a video to prove it. :-) But this isn't the primary reason for this message, just related, maybe.)

The above external monitor sleeping problem occurs once or twice a day, non-deterministically, and I've determined three (3) ways to get the MBP to behave normally, again, once it does happen:

(Way 1 - Works 99% of the time; if not, try again; if it still doesn't work, use Way 2)

  1. Disconnect external monitor (from Thunderbolt port closest to power connector);
  2. Put MBP to sleep by closing the lid and waiting for 15 seconds (if I open the lid too quickly (and notice that the Retina display looks as if it never turned off), this procedure doesn't work, so I shut the lid and wait 15 seconds again until it does appear that the Retina display turned off);
  3. Open MBP lid, pressing the space bar if the Retina display doesn't come back alive shortly after opening the lid;
  4. Reconnect the eternal monitor (to Thunderbolt port closest to power connector);
  5. See if the problem is fixed by moving the track pad pointer to a hot-corner allocated to sleep the MBP.

(Way 2 - Works the rest of the time when Way 1 doesn't work.)

  1. Reset the SMC.

(Way 3 - This way is still being checked out, but shows 48 hours of promise.)

  1. Connect the external monitor to the Thunderbolt port farthest away from the power connector. I hypothesized this as a fix 2 days ago, and the problem has not returned since I moved the display connector to the front Thunderbolt port. I've moved the connecter back to the supposed problematic Thunderbolt port a few hours ago i.e. the rear Thunderbolt port closest to the power supply connector. I want to see if the problem re-surfaces before I show the Geniuses over at Apple my video tomorrow afternoon.

Follow-on question: Are the Thunderbolt ports "symmetric?" That is to say, is there any "hardware difference" between the two ports? To answer my own question, at least partly, the rear Thunderbolt port appears to be hotter i.e. when I place my finger on the aluminum above the back port and when I place my finger on the aluminum above the front port, it feels to me that the back port aluminum is hotter, hence, there does appear to be a difference in the operating temperature near the two ports' physical connections.

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Related: apple.stackexchange.com/questions/7684 –  starlocke Jan 2 at 14:47
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