I Fried my duet, and I have no idea how



  • Well, I have half an idea how. I shorted some LED tape by accident that were hooked directly into the 24v supply and everything turned off. The supply is fine, the duet got burned.

    Here is where it gets weird though, its blown the 3.3v line on the duet. 5v line is still fine (as far as the red LED lights up). I can't connect to the interface, or through usb.

    I've taken a lot of care on this build… The duet is isolated from the frame with plastic mounts and nylon screws, the wiring is neat and nothing peculiar. Surely a short on the VIN rail at 24v should not cause this? From what I gather the board is quite protected from over voltage at this point. I also had absolutely no magic smoke to suggest that something went seriously wrong... it just turned off.

    To make matters worse, I've only had the board hooked up to the printer for a few days! I've ordered a replacement board as I'm on a tight deadline, but I would love to know how I killed this board. I feel it may warrant extra investigation



  • Maybe the 3.3v regulator died. Can you supply 3.3v via the expansion connector see if it will boot up?


  • administrators

    I am sorry to hear of your misfortune. If the short was on a 24V circuit connected directly to the power supply, I can only guess that this caused a large transient on the 24V rail, and this transient exceeded the 30V rating of the stepper drivers or the 40V rating of the 5V regulator IC.

    Which revision Duet PCB is it?



  • As far as I can see, it is V1.02, according to the writing in the center of the board. It is the duet ethernet version. The board blew around 6'o clock yesterday though and the self resetting fuses (if that was the problem) don't appear to have kicked in.

    I have no means of applying 3.3v to the board unfortunately to see if that helps. I know the vin line is working, as the fans turn on still and the blue vin led still works, along with the red 5v led when I plug in USB.

    I'm surprised to see that such a short has caused this to the board though. According to the 'How to destroy a duet' guide, its quite hard to achieve this, hence why I started the topic. Could one of the protection methods built in to the board be faulty? I would be willing to send this back to you guys to see what you think


  • administrators

    Is there any way (other than via the VIN connection from the power supply to the Duet) that the LEDs blowing could have (temporarily) put 24V into the Duet 3.3V circuit (like for example were the LEDS routed with thermistor wires?)

    If not then its as David says - temporary over-voltage on VIN above the the stepper driver maximum if the 5V circuit is working correctly.



  • The LEDs were not routed with any thermistors, they were wired direct to power supply just to illuminate the whole printer. Hence why I'm surprised that this has caused the board to blow. There were no nearby components and none of the wires are damaged (I have checked today) I thought it was extremely difficult for a simple short at the power supply to cause this? This leads me to believe a possible fault with the boards protection features



  • are your endstops shorted? It sure sounds like the 3.3v regulator isn’t working. Did you try unplugging all the connections to the board?



  • Yes, as said I checked all my connections and wiring. This printer is for a client and so all wiring has been checked, checked and triple checked.

    The 24v short happened when I was installing some 5050 LED tape. The end of the tape was exposed where the tape was cut and touched the bench whilst I was testing them. Complete oversight for me, and I've now insulated the ends of all my leds. The printer immediately turned off to only find that the 3.3v line has fried. According to their own guide, this should be next to impossible to do so I'm fairly certain something else is wrong that shouldn't be. This sort of fault should only happen if you accidentally load 12/24v into the z probe or similar outputs and I don't even have a z probe



  • I know you’ve checked the wiring but is there any possibility at all that one of your endstops has a short to the frame of your printer. A single stray strand or a bit of nicked insulation is easy to miss and hard to spot without putting a meter on it.

    From from your description of the initial incident it sounds like you have a metal (or at least conductive) work surface. If this is the case and you had a short from the power or signal line of an enstop to the frame there could have briefly been a direct route from the 24V supply to the 3.3V circuitry via the printer frame.

    Qdeathstars suggestion of disconnecting everything is a good one. It sounds like your board is terminal but testing it in isolation may yield some unexpected good news.



  • can’t know if the board is terminal until you have 3.3v on the 3.3v rail. A coin cell might provide enough power to do a quick test….


 

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