[sf-lug] Weird USB problem, maybe hardware

[Akkana Peck]

I'm having a weird problem with my Carbon X1's USB ports, and
I can't figure out how to summarize the problem in order to search
for solutions.

My old Kobo ebook reader, when plugged in to a computer, pops up a
dialog saying a computer was detected, do I want to connect to it?
(At this point, the computer won't show anything in dmesg.) If I say
yes, the Kobo connects as two mountable usb-storage devices (sda is
the internal filesystem, sdb is the SD card). If no, it just charges
and the computer never sees it.

Lately, none of this works on the CX1, because the first part,
the Kobo detecting there's a computer on the other end of the USB
cable, doesn't happen. The Kobo sees that it can charge, but it
never presents the "connect?" dialog, so it never creates the
usb-storage devices so I can mount them. There's nothing in dmesg.

The thing is, I can't even figure out how to do a web search for
this problem. What is it that makes a computer's USB port look
different from a charge-only port? And is there a searchable term
for that? All the keywords I've thought of lead to pages on getting
computers to detect a USB device, not how to get the computer to be
detectable BY a device.

Other USB devices (storage, camera, microphone, Android phone)
work fine on the CX1, so it's not that USB is dead.

I've tried:
- three different USB A-to-micro cables
- different USB ports (the laptop's built-in USB3 ports, plus a
  powered USB2 hub connected to the other USB3 port)
- same Kobo and cable on an older laptop running a 2-year-old Debian
  (works fine, the Kobo shows the connect? dialog)
- Kobo and cable on the husband's Mac (shows the dialog)
- rebooting the CX1 into an older Ubuntu where this used to work
  (still no dialog, suggesting this is a hardware failure?)

I tried a voltmeter on the CX1 USB3 port, a port on the USB2 hub,
the USB2 port on the old laptop, and a cheap charge-only adapter.
All four gave +5 V on pin 1 (5.14 for the CX1's built-in USB3), 0 on
all the others. So whatever the difference is, it's not detectable
by a simple voltmeter test.

Anyone know what makes a computer's USB port look different from a
charge-only port? And is there a way to fix it if it fails?

        ...Akkana