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Jus12
Asked: 2020-08-29 10:54:26 +0800 CST

Certain USB-C cable / port combination not working

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I have a USB extension hub with the following specs (ASCII art is worth 10000 words):

                  ----------------------- 
                  |                     | 
                  |               [Type A female] -> output 1
   Input -> [Type A female]       [Type A female] -> output 2
                  |               [Type A female] -> output 3
                 LED              [Type A female] -> output 4
                  |                     | 
                  -----------------------

I have the following cables cables:

  1. (Type A male) <--> (Type A male)
  2. (Type C male) <--> (Type A male)
  3. (Type C male) <--> (Type C male)

My Ubuntu box has both Type A and Type C female connectors. I also have an external SSD that has a Type C female connector.

The combination of cable 2, my Ubuntu desktop and the hub does not work. In summary, the following combinations have been tried:

 | Cable # | Cable side one   | Cable side two   | works? | Conclusion          |
 --------------------------------------------------------------------------------
 |    1    | Desktop Type A   | USB hub input A  | yes    | USB hub works       |      
 |    2    | Desktop Type C   | USB hub input A  | No     | ???                 |
 |    2    | Desktop Type A   | SSD input C      | yes    | Cable #2 works      |     
 |    3    | Desktop Type C   | SSD input C      | yes    | Desktop Type C works|

The table shows that alone each of the three work (Desktop Type C, USB hub and Cable #2). However, the combination does not. What could be the reason?

networking usb usb-c 20.04

1 Answers

  1. I believe I found your problem, it's the hub and cable not adhering to the USB spec. Here's the evidence:

    (Type A male) <--> (Type A male)

    And this:

    By work, I mean the LED comes on (also have tested it to actually work).

    A cable that complies with the USB spec is not supposed to be able to have a male USB-A connector on both ends and still provide power.

    Here's an example of a USB-A to USB-A cable that meets the spec: https://www.datapro.net/products/usb-3-0-super-speed-a-a-debugging-cable.html

    In the description it points out that a compliant cable leaves the USB D+/D- and 5V pins unconnected. Your USB-A to USB-C cable will connect the power pins on both connectors but it's "smart" enough not to supply power to a cable with a USB-A male end on it as the USB spec does not allow USB-A ports to take in power.

    Do yourself a favor, and a favor to anyone around you, and destroy that cable and hub before someone uses that non-compliant cable in something other than that hub and starts a fire or something.

    Replacing this hub with one that is new and complies with the spec would be something like $20. Not replacing it runs the risk of far more damage than $20. Take that cable and cut it in pieces so no one else picks it out of the trash to use. Drop a brick on the hub too while you are at it. Then go buy a new hub.

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