Diagnosing a probably bricked Duet2



  • Hi, this is my first post and I'd like to announce that I probably scored an 8/10 on the "how to destroy you Duet2" guide. I managed to misplace one z probe wire and shorted it with the heater. The board lighted up as if it was Christmas and quickly I disconnected it from power (24v).

    Now, when I connect the board to my desktop via USB, only the 5v and USB power leds light up and the board is not detected by the computer's OS. I have followed all the steps in the wiki, nothing worked.

    I have a moderate knowledge in electronics and started to diagnose the board. The first thing I found out is that, when connected to the USB power, the U2 regulator is outputting 0.55v to the 3.3v rail and the 3.3v pin of the z probe has the same voltage reading. When the power comes from VIN 24v, the z probe connector 3.3v pin reads 0.68v. There is no reading on the U2 pins.

    I'd like to know if I should replace the U2 regulator or if there are any further steps that I should follow to get the correct diagnose of my board's problem.

    Thanks in advance



  • U2? Which Duet 2 do you have?

    But yeah, if the voltage regulators aren't doing their job then I'd start by removing the regulator, measure the impedance on the regulators output pads (i.e. on the board) and possibly feed in power from a current limited bench supply to see what else may or may not heat up, and keep removing parts until you have a nominal current draw, then start soldering in replacements.


  • administrators

    If you shorted the heater wire to the +3.3V pin on the Z probe connector, that's bad news (a short to any of the other pins would probably have been survived). At the vert least the WiFi module and the SD card will have failed. Probably also the 3.3V regulator and the processor. Maybe also the stepper drivers and the 74HCT02 mosfet buffer.

    If you have an external 3.3v PSU then I suggest you remove the SD card, apply 3.3v to the Z probe 3.3V pin, and see what components on the Duet are getting hot. Most likely it's one or more of the 3.3V regulator chip, the WiFi module, the 74HCT02 and the main processor. Then with hot air equipment, you could remove that component and repeat.

    BTW we're aware that users sometimes have these types of short, so on Duet 3 we've taken great pains to protect it against even a short between +24V and the external +3.3V pins.



  • @bearer said in Diagnosing a probably bricked Duet2:

    U2? Which Duet 2 do you have?

    But yeah, if the voltage regulators aren't doing their job then I'd start by removing the regulator, measure the impedance on the regulators output pads (i.e. on the board) and possibly feed in power from a current limited bench supply to see what else may or may not heat up, and keep removing parts until you have a nominal current draw, then start soldering in replacements.

    Sorry, it's a Duet2 1.04b

    @dc42 said in Diagnosing a probably bricked Duet2:

    At the vert least the WiFi module and the SD card will have failed.

    Yes, the Wifi module does not light up it's blue led.

    @dc42 said in Diagnosing a probably bricked Duet2:

    Probably also the 3.3V regulator and the processor.

    Is there a way I can test this while powered to VIN 24v or USB, before I try the external 3.3v PSU?


  • administrators

    @kauedg said in Diagnosing a probably bricked Duet2:

    Is there a way I can test this while powered to VIN 24v or USB, before I try the external 3.3v PSU?

    You can remove the SD card and if the 3.3V rail is still at much less than 3.3V, see whether any chip or the Wifi module is getting hot.



  • @dc42

    My room temp is about 25C but no component is above 31C. Checked the wifi module, U11, U2, steppers, processor... Nothing seems out of the ordinary. I believe the U11 is the 3.3v regulator.

    Unfortunately I don't have a 3.3 ext PSU.



  • (if you happen to have an arduino board or similar you could perhaps borrow 3.3v from that)



  • @bearer Excellent idea!

    Did this and now the Duet2 board is detected by the OS and I can connect to it using Pronterface. Should I try inserting the SD card now?

    Bus 001 Device 022: ID 1d50:60ec OpenMoko, Inc. Duet 3D Printer Controller



  • Oh, you might have gotten lucky! I'd look up the datasheet for both 3v3 regulators and just swap them if pin compatible and sufficient current on the arduino one.



  • God, I'm so relieved!

    What component is the regulator I must replace? I've been wandering around the KiCad project but I'm a real noob at this



  • I'd keep the champagne in the fridge till you test the drivers and everything else.

    If the board didn't work with usb but does with external 3v3, then U2 is probably toast at least. I'd remove that, then test if you get 5v with 24v applied (before installing the new U2)



  • @bearer Yeah, I have a presentation to write right now but I'll do a full test, connecting the board to my Voron. If the processor is alive, it's a great thing already. I'll start replacing U2 (no pun intended).



  • I've replaced the U2 voltage regulator of my Duet2 board but the component is still outputting 0.3v and works fine using an Arduino on the 3.3v rail, as recommended.

    How can I diagnose the C4 capacitor of the 3.3v regulation system?



  • @dc42 said in Diagnosing a probably bricked Duet2:

    so on Duet 3 we've taken great pains to protect it against even a short between +24V and the external +3.3V pins.

    not directly related to the topic but..

    I made (with a friend) an ethernet stepper controller (similar to MESA 76ixxE cards only with Virtex FPGA instead of Spartan so ethernet in, stepper/servo/encoder/sensors signals in-out) and protecting all io's was not too hard, for digital input simple 5 to 36V differential 1MHz opto inputs are not that expensive, for outputs 1000V isolated 2MHz differential outputs are also fairly cheap.. user can do anything with input/output the board will survive.. (as long as user don't short anything on board 😄 that's why board is in case 😄 ) ... if duet3 is to be used in industry having everything 36V (or 48V depends on industry) safe is kinda must 😄

    now for analog inputs we use mcu that's talking spi with fpga and that spi is 1000V isolated so in case of crap entering analog input mcu can die (there is a spark, shottky from vss and to vcc, a ferule bead and few tantalums but ... still) it was cheaper solution than opto isolated linear opamp that would be a better solution (but you can get 10 mcu's for the price of that opamp 😞 so mcu it is)



  • @kauedg said in Diagnosing a probably bricked Duet2:

    How can I diagnose the C4 capacitor of the 3.3v regulation system?

    good in-circuit esr tester would be the easiest thing, but, when you blow the circuit like that I always recommend replacing all capacitors on the power rail, especially main output cap like C4 in this case... so just trash it and put a new one in, will save you lot of grief later 🙂


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