I use two Thunderbolt displays with my mid-2012 retina MacBook Pro. I keep my iPhone 5 in a dock hooked up to the left Thunderbolt display via USB. On Friday, I noticed that when I went to commute home, my battery was very low. Odd! Today, I noticed that sitting my phone in its dock didn't make the charging lightning bolt show up next to the battery indicator.

A few minutes of testing proved that all three USB ports on the left Thunderbolt monitor are failing to charge my phone. Using the same cable in the other Thunderbolt monitor, or in the laptop itself, behaves exactly as expected.

How do I go about troubleshooting these USB ports?

UPDATE: OS X (10.9.2) also does not see the camera on the left-hand Thunderbolt display, and won't send sound out through it, either. It's not just the USB ports, clearly. How do I troubleshoot, uh, everything-but-the-screen?

UPDATE 2: From a suggestion in the comments, here are the System Report details on USB, Cameras, and Audio:

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  • First thing I'd look at is the system report, to get a better idea of what the system sees. Click the apple menu in the upper left. Click "about this mac." Click "More info" button. Click "System Report." From there you can click on "camera" to get a list of currently seen Facetime cameras, and "USB" to see what USB devices and buses are seen. – Bart Silverstrim Apr 28 '14 at 17:58
  • @BartSilverstrim Post updated. – hairboat Apr 28 '14 at 18:09
  • I'm thinking I'll try resetting the SMC before I go home tonight. – hairboat Apr 28 '14 at 18:18
  • Try that reset, and you said the display is working so while the cable seating shouldn't be a problem it wouldn't hurt to reseat (remove and replace) the cables as well. If that fails I'm apt to suspect a possible problem with a controller on the display. There might be something in the logs as well (the "Console" application will display those, but unless you're used to reading Matrix glyphs it may be hard to interpret.) – Bart Silverstrim Apr 28 '14 at 18:25
  • SMC reset solved it. Case closed. – hairboat Apr 28 '14 at 18:54

I never figured out what the problem was, but it went away when I reset the SMC.

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