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Thread: USB2AX seems broken

  1. Re: USB2AX seems broken

    Definitely looks like a cold solder joint, which temporarily connected while you were probing. And most probably on the MCU.
    Probably can be fixed in 2s with some flux and a flat tip iron if you are brave enough, but in the end when you have one, you could have others waiting to break after some vibration.
    Better change it, sorry.
    Personal blog:
    USB2AX documentation:

  2. Re: USB2AX seems broken

    Thank you Xevel! I've opened a ticket with Trossen and hope to hear from them soon! Kind regards, -- Ihab Awad

  3. Re: USB2AX seems broken

    Hi again,

    I got a new USB2AX from Trossen and tried it and here are the results.

    With no 12V power applied, between the DATA and GND pins, a scan produces the following trace:

    Zooming in on the various pieces, they are:

    I did not protocol-analyze these segments but they look like TTL square waves to my untrained eyes.

    I then applied 12V power using my "Y" cable. The traces became VERY NOISY to the tune of +/- 3 volts. I could not figure out why, and I think I smelled a burning smell. I am sorry but I did not save any of the traces during that period. In any case, it would not be surprising that any device on that line would not recognize the signals as valid serial data -- it was really horrible.

    Subsequently, the USB2AX behaved in the "broken" state. Here is what a scan *now* looks like without 12V power applied:

    and with 12V power applied:

    So I guess my USB2AX was good and is now broken. I don't know how I could have broken it though. I checked and re-checked the voltage on my wires and it seemed fine. VDD - GND was 12 volts; and the DATA line in my "Y" cable is not even touched at all.


  4. Re: USB2AX seems broken

    Here is one more thought. I looked at my Y cable and noticed a possible difference from how it "should" be. This diagram should explain:

    Click image for larger version. 

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    I looked at the schematics and layout for the USB2AX again in Eagle and it seems to me that indeed the VBUS signal in connector DXL1 is indeed just a lone through-hole connected to nothing. So having the +12V routed back to the USB2AX should not cause any problems.

    But I just got through spending a month debugging a circuit only to have a more experienced person look at my board and tell me that the soldermask was off by a fraction of a millimeter, which caused a short circuit which was in some cases intermittent. Drove me crazy!

    So here is a hypothesis:

    1. The current production run of the USB2AX has some random production flaw where +12V is being routed into something it should not be;

    2. Meanwhile, most people create their Y cables in such a way so that +12V is not routed back to the USB2AX

    3. I am the only person in the universe dumb enough to create a Y cable the way I did, with +12V going back to the USB2AX; and so

    4. I happen to be the only one to have encountered this problem.

    I honestly don't know if that is the case.

    You may ask why I am not using the 6-port power hub from Trossen:

    Well I ordered the full Trossen servo manager kit:

    It seemed like the 6-port hub was missing, but it could have been my fault since I had unpacked the kit in a bit of a hurry while busy with other things. So I just decided making a "Y" cable was easy enough anyway, and went ahead and made one.

    But looking at the 6-port hub, it appears the connection back to the USB2AX is not "special" -- meaning that the Trossen hub must bring the +12V signal to *all* the middle pins of its connectors, meaning that with this hub, the USB2AX would indeed "see" +12V on its VBUS terminal. So if I had been using the Trossen hub, I would have subjected my USB2AX to the same conditions.

    I'm rather confused.


  5. #15

    Re: USB2AX seems broken

    The USB2AX is fine with a voltage on the VBUS line.

  6. Re: USB2AX seems broken

    Cool. And *Xevel* said it's even ok with 12V on the DATA line as well. So I'm puzzled as to what I could possibly have done.


  7. Re: USB2AX seems broken

    Yeah, connecting the 12V pin on the USB2AX shoukd not be a problem, it's not internally connected to anything. And like already mentioned a few times, the DATA pin of the USB2AX *should* survive 12v with no sweat whatsoever.
    This is all very annoying...
    PM me your address, and I'll send you another one, and I'll also give you an address to send the ones you have.

    Sorry for all that lost time
    Personal blog:
    USB2AX documentation:

  8. Re: USB2AX seems broken

    The only way I could think would damage stuff would be if on the USB2AX you had some crazy inversion of pins, like 12V on USB2AX GND, and GND on USB2AX DATA (it is not protected against -12V). But to appear it would require a lot of misunderstanding, and from the pictures you posted it should not have happened...
    Personal blog:
    USB2AX documentation:

  9. Re: USB2AX seems broken

    Thank you Xevel! Here's what I've done. I have ordered:

    * A new USB2AX v3.2a
    * The Trossen 6-port hub

    With these and the Trossen 12V power supply, my setup will be 100% store-bought per the Trossen servo manager kit. I will repeat my tests and try to gather as much oscilloscope data on every step. If my problems are fixed, then either it was my fault or I just had a run of two bad USB2AX units. If not, then we have a well-defined baseline for trouble shooting. In either case, I will be happy to send you the damaged units and we can decide how to proceed from there.

    Kind regards,

    Ihab Awad

  10. #20

    Re: USB2AX seems broken

    Note that, if you're using the AX-12a pinout description in the manual, it is super confusing. The description of which pin is which is ordered "wrong" compared to the ports you see; you have to actually trace the wire drawings (which invert at some point) to see which is which.

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