PLUTO dead: possible cause

  • Thanks to DL5QY sending me his dead PLUTO, I was able to trace down the problem and offer an explanation for the probable cause.

    TLDR: GND potential difference between SMA and USB frying L7 which then shorts the internal 5V line.
    A more detailed diagnosis is attached in the zipped PDF.

  • HI,

    Good catch... I had the same problem.. And I started debugging.. I was seeing short circuit in powe rlines (even in USB input)...

    I thought the voltage selector U8 or U9 is the reason.. :( I didn't want to desolder them, because they were very tiny to resolder back.

    I never thought that it can be the L7.

    Desoldered U8 and U9 didn't give me a solution but then I was sure that it is L7.... Just in your photos it was shortcircuited internally. I just placed wires instead of the coil L7, and carried the USB power from P2 pin 1 (Data USB power pin) to D3 (or shorted L7 power lines). Also removed the F1 fuse and D2.


    What does all this mean... No voltage selection for data USB and/or Power USB plug.. Which means I cannot power USB ethernet or similar OTG devices.


    Now the device has LEDs back.... Checked the voltage test points and all seems fine. But LED1 is blinking twice every seconds and I cannot have the USB drive present on PC side.. even IIO_INFO command cannot find any device...



    Anybody with any ideas ?




    Thanks

    Baris DINC

    73's de

    OH2UDS / TA7W

  • I will document my progress here, someone else can face the same issue...


    I connected a serial/USB converter to RX and TX pins on the JTAG port (be carefull it is 1V8 , you may want to use a level shifter)..


    I used 3V3 USB serial converter (worse case to loose the whole device...)


    Now I have the console.... I will investigate why I don't see any action on the USB port side :(



    73's de OH2UDS / TA7W

    Baris

  • I re-solder the F1 fuse back.. This allows the device to sense the USB connection..


    after resoldering F1, when I put the device into DFU mode (press user button and plug in usb power) I was able to see the dfu interface on usb (id 0456)..


    Then used the firmware and dfu-util to flash the latest firmware


    sudo dfu-util -a firmware.dfu -D pluto.dfu


    and the device started back to working as normal....


    sanother PLUTO recovered :)



    73's de OH2UDS/TA7W

    Baris

  • I had another GND strike on my second PLUTO today... This time I was not so lucky. I lost the laptop computer totally.... And the pluto..

    I can still have console on plutor using the JTAG Rx and TX pins but this time the USB chip looks died (USB3320C-EZK).


    The internal LDO 3v3 is not providing output so the device assumes itself in OTG mode.... I will try to replace the USB3320C-EZK

  • oh2uds it seems you have a severe ground loop problem and as USB is not galvanically isolated, this will lead to future defects unless fixed. You have to break the loop somewhere, either by inserting a capacitor in the SMA GND input or using an OTG USB-Ethernet adapter (Ethernet is galvanically isolated).

  • Hi,

    I accidently applied 12V to USB power socket and killed my Pluto. On inspection found L7 getting hot and pluto drawing excessive current with resistance between D3 (TVS DIODE) and ground showing only 45 ohms. Removed D3 and L7 resistance jumped to 4.5k. Do I have to short both primary and secondary pads from where I removed L7 to power up pluto or only primary side is to be jumpered? If pluto does not wake up what else could be damaged/checked?

    73

    Syed

  • Thanks Rocco for the tip.I connected the wires across both the pads of L7 and powered through P2 or P3,still no LEDs light up. I forgot to mention L7 checks ok, no shorts. The short is between either USB (P2 or P3) pin 1 and PG. Since fuse F1 is ok, I suspect U8,U9 and U16. The max voltage for these devices is 6.5v. Obviously 12v will destroy these. Next step will be to isolate PG and apply 5V direct at D3.

    73 Syed

  • I had another GND strike on my second PLUTO today... This time I was not so lucky. I lost the laptop computer totally.... And the pluto..

    I can still have console on plutor using the JTAG Rx and TX pins but this time the USB chip looks died (USB3320C-EZK).


    The internal LDO 3v3 is not providing output so the device assumes itself in OTG mode.... I will try to replace the USB3320C-EZK


    Yes exactly true.... and got the second strike and lost the USB3320 this time.... I checked that the FPGA side is still alive by connecting JTAG.. and after replacing the USB3320 the device came back alive "once more"...... I will be much more carefull this time...



    73's de OH2UDS/TA7W

    Baris Dinc