For a long while now I've experienced USB devices intermittently disconnecting on my Macbook Pro Retina 2012 (El Capitan 10.11.2).

I'm currently using a Targus 7 port USB 3 hub (http://targus.com/au/usb-30-7-port-hub-with-fast-charging) but this problem existed when I was using an older USB hub. I bought this one in the hope it might resolve this problem, but it didn't.

This USB hub is connected to its power adaptor.

From memory this problem also existed before El Capitan update.

For work I use Microsoft Lync for Mac, and I sometimes notice than when a new instant message arrives, my keyboard, mouse and headset will disconnect. But they also sometimes disconnect without this trigger.

To reconnect them, bizarrely, i seem to need to unplug and replug each device in 3 times specifically.

It's very frustrating and inefficient for my workflow. Just wondering if there are any suggestions or recommendations as to how I can troubleshoot or resolve this?

Following are screenshots of the USB map (two separate screenshots as the contents of the USB 3.0 Bus details page didn't fit in one screen)

Page 1

Page 2

  • Was your Logitech Keyboard light on when you made this screen capture? If not, do it and pay attention to the field: Current Required (mA).
    – dan
    Commented Aug 10, 2016 at 17:35
  • @danielAzuelos The keyboard light was on when I made the screen capture. I did a further test by turning the light off and reconnecting the keyboard, then re-opening the USB map, and it seems the Current Required (mA) remains the same at 300. I tested with the light on again, and it's 300 every time.
    – Manachi
    Commented Aug 10, 2016 at 23:23

2 Answers 2


Disclaimer: this is an answer under construction.

Open the  > About This Mac > System Report..., select Hardware > USB, and open every small ▼.

Select the USB bus where is connected your USB hub, and enlarge the lower part of the window to have a complete vue of all your USB equipments.

Make a screen capture: commandshift4, space, select the USB map window and click. You will get something like:USB config

Include this screen capture within your OQ (original question).

Verify that the sum of the Current Required (mA) of all the equipments connected to the same internal USB hub don't exceed the Current Available (mA) for the hub. This value might be different depending on the USB port available outside and what is already connected on it internally.

As a basic simple rule, avoid the external USB port which is on the bus where is connected the FaceTime HD camera (Current Required (mA) = 500 mA). For example, on a MacBook Pro, I discovered through trials that my FaceTime HD camera is on the bus with the USB external port nearest from the front.

To check this hidden cabling, just use your external mouse.

Connect it on port nearest from the front. Hit commandR in System Report... to refresh the USB connection information. Note on which bus is this external USB port.

Repeat the same operation for port farthest from the front.

  • 1
    Thanks, I've awarded you the bounty because your help was so thorough and taught me (and will teach others) about how to troubleshoot this issue clearly and accurately. thanks! I've answered the question separately because my particular scenario seems to have been a very specific and unexpected solution, but one that I think may help others.
    – Manachi
    Commented Aug 16, 2016 at 0:47

After trying every possible combination of hubs and configurations I could try, and with the very helpful guidance of daniel Azuelos (other answer) it turns out that in my scenario, everything started working seemlessly when I attached a USB 2 hub to the USB 2 port in my Macbook Pro (on the left), and attached only USB 2 devices to that hub.

I attached the USB 3 hub to the USB 3 port (on the right) and attached only USB 3 devices to that hub.

It seems when doing this everything stays connected and stable.

In particular the problem seemed to be arising when having USB 2 devices attached to any hub on the USB 3 port (regardless of whether the hub was USB 2 or USB 3). I don't know why this behaviour occurs, but keeping 'like with like' has worked in my situation.

Interestingly, the USB 2 hub is unpowered.

I do audio production meaning I sometimes use a LOT of USB devices, including eLicensers, an audio interface, synthesisers etc. And the USB 2 devices just did not like being on the USB 3 port.

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