Dead USB port on Windows tablet

[brainwash]

I don't have high hopes for this but perhaps it can still be revived.
I have a laptop/convertible Atom thingie which has worked pretty flawlessly until recently. Now the usb port does not recognize (negotiate) any device, but it provides power to the port. I think last time I tried to plug something into the USB it was a DigiStump Arduino thing which might've had the data lines connected to something (5V or perhaps even 12V or ground). The tablet stopped seeing it but I could program it with my larger laptop, so not sure what went wrong there.

The internal USB still works, the detachable keyboard and touchpad work through it but it's based on 3.3V, probably with some SPI to USB converter. So I can see a USB3.0 hub in device manager that is disconnected when the keyboard is detached.

The external micro-USB port is a 2.0. I get 5V on the power line and 0V (not floating, it seems) on the data lines. I could not detect any shorts.

Here are some pictures of the board and arrangement:
http://imgur.com/a/QgMIc

I could possibly rule out a dead USB port if the internal port is working, but I'm not sure on that. I tested the SOT-23-3 devices in the vicinity of the port and could not find any shorts or breaks. I don't know if there are any fuses, the white components on the front side look to be caps (one pin goes to ground).

I'm not familiar with how USB ports are designed, perhaps someone can give a hint on what I can test and what the path for troubleshooting should be.

EDIT: for clarification, this is not a software/driver issue. I've tried to boot off of a USB stick, tried various peripherals, tried to use a powered usb hub. It just looks like the data lines are not doing anything but 5V is fine. For reference, the charging port on the tablet takes 5V.

[Rasz]

you  could look for esd protection chip in line with usb data lines, or maybe external termination resistors
but seeing separate 5v charging barrel socket tells me its one of those ~$100 chinese garbage tablets where they couldnt even be bothered to budget for proper usb charging switch = they probably used japanese school of cost optimization aka removed every single non essential component

[brainwash]

I was able to trace the differential signals to some pads near the SoC after which they probably become buried. Since it seems like a direct connection from the port to the SoC the port is probably dead on the chip itself. I could not find anything that looks like a usb hub chip or something similar.
Since AFAIK the USB data signals should not be routed out (split) the only explanation is that the 'test' points near the SoC are the only connection to the external port.

The 5V USB rail is 'isolated' from the 5V charging rail. Probably the circuit is Vcc 5V -> PMIC -> Vbatt (4.2V) -> 5V USB. Obviously the switching on the PMIC would be smarter, but I'm all out of ASCII art today.

Anyway, not a huge deal, but I should probably look for something more rugged as my lab laptop. Hopefully something like the Thinkpad X230 doesn't have these kind of issues. I was initially looking at a Macbook Air as a replacement but I don't think it would withstand connecting various [problematic] lab equipment to it.

[Rasz]

raspberry PEE is great for usb shenanigans in the lab, you can either log in remotely or use USB over IP
you get perfect isolation (wifi + battery)
works great for everything not requiring set in stone usb 2.0 bandwidths (those would be for example cheap usb logic analysers or sdr)

[brainwash]

The PI would normally be an interesting proposition but it's too slow for most tasks. I have a gen 1 that's barely able to run OctoPI for my 3d printer, and that's without any slicing.
A Pi3 (35E) + dongle (7E) + supply (7E) + battery (5E) + screen (10-50E) + trackpad keyboard (20E) is a mess of wires and already costs more than an i5 laptop that can run circles around it. I have rPi(s) around the house and a bananapi, they are limited to headless servers. Even Kodi runs much faster on a 20E android box. Plus with a laptop you get the convenience of dual-booting, for those times you need Windows. That's just my rant on the subject.
The single advantage is that if you burn it you can replace it with another one and you're good to go.

Back on topic: before putting the cheap laptop back together I've checked the USB data lines. I have 0V on D-, 0V on D+ with no device and 3V on D+ with a device connected and no signal edges. Since I see no other connections I have to assume again that the port on the SoC is destroyed. Anyway, a replacement 'laptop' with a broken touchscreen or similar is <50E and a used one can be had with a bit of hunting for ~70E. Would've been nice if debugging it was possible.

[ReddBeardd]

if you hit the USB port with voltage going the wrong way -  just be glad the device works at all -  that port is done.if using a usb device is mandatory -  either replace the tablet -  or get a router that allows for a networked usb port -  my dlink  will even let me plug in a mouse or keyboard to the router and use it on any windows device attached to the router -  same for anything else usb -  even a pair of logitech g930 headphones.

[Rasz]

The PI would normally be an interesting proposition but it's too slow for most tasks. I have a gen 1 that's barely able to run OctoPI for my 3d printer, and that's without any slicing.
A Pi3 (35E) + dongle (7E) + supply (7E) + battery (5E) + screen (10-50E) + trackpad keyboard (20E) is a mess of wires and already costs more than an i5 laptop that can run circles around it. I have rPi(s) around the house and a bananapi, they are limited to headless servers. Even Kodi runs much faster on a 20E android box. Plus with a laptop you get the convenience of dual-booting, for those times you need Windows. That's just my rant on the subject.

you misunderstood me
either log in remotely - as in SSH over the network into the PEE(orange/whatever other cheap arm devboard) and run command line tools there, like openocd/gdb serial terminal or firmware flashers
or use remote usb on your current laptop/tablet https://www.raspberrypi.org/forums/viewtopic.php?f=36&t=36851

the only thing you could feasibly fix would be bad usb socket on this chinese crap - check if there is a good connection between pins and actual tracks, other than that its over (good luck sourcing replacement atom and reballing)

[brainwash]

@ReddBeardd: I'm glad that everything still works but was intrigued by the fact that another USB port was still working. I hoped it was only a fuse/inductor/transistor that could be replaced. I have a router with USB support (Fritz) but it's a bit far away and everything in the house relies on it.

@Rasz: rPi is totally inappropriate for my workflow but you just gave me an idea. I have a few bench instruments with USB (multimeter, supply, soldering station, oscilloscope, siggen, bench projects with dev boards) and using them via ssh or even X11 is painful. But perhaps they can work with USBIP / usb over ip, which would let me use them with both windows and linux.
Reballing the Atom SoC is not a dealbreaker, but it is when similarly used tablets go for 70E on ebay.


The main use case for my little laptop is watching youtube, but it shines when travelling and I need to back up my stuff to Google Photos. For that I bought a small-ish wireless NAS which, while slow, could provide everything needed. The other use case is: once a year I might need to hook up a diagnose cable to a car, which needs windows. For everything else I use a BT-OBD adapter which works just fine with Android. Even photo backup is doable with Android and OTG, I did that 4 years ago when I was backpacking for a month or so.
And the other use-case is programming devboards in remote locations but that can be mostly replaced with ESP8266-UART bridge.

So probably the only real thing I need is a very small portable USB router/nas thing. The Zsun one ( http://www.gearbest.com/memory-cards/pp_246129.html ) looks promising but it lacks a separate usb port.
I will still buy an 'ultrabook' like X230 or E6320 or X1 carbon which can be had really cheap now for the other use cases. Hopefully they have protection.

[brainwash]

Just wanted to close this topic, as the issue has been resolved a few months ago.

Basically, the docking port (5 pins) provides power and USB signals from the tablet to the docked keyboard.
So I just bought a few random 1$ USB hubs to see which would fit the best. Then I soldered the stripped hub in series with the existing keyboard/touchpad controller.  I went through 3 hubs doing this, they randomly quit working or were just faulty to begin with. The joy of AliExpress... Also, the most promising (compact) hub was only USB1.1.

The keyboard controller was wired to one of the ports, another port was brought out with a micro-USB female connector. I still have 2 extra ports, my intention was to bring out a full-sized USB female connector, but the folding mechanics and space constraints worked against that.

I gave the "laptop" away eventually, but I still miss the great battery life and great screen. I don't miss the Atom architecture which is the Celeron of today. Hot, slow and draining, just like dating a supermodel. But cheap.

LE: USB over IP is still crap. Tried everything under the sun. I could only get a commercial solution working, which limits you to one device.

http://imgur.com/a/pNEil