Mistery smoke on 6HC

  • Hello,
    Something odd happened to my Duet 6HC v1.0 WD31943 + 3HC hook up with a RPi4.

    I was trying to read a sensor connected at the 3HC.out4 using M409 command. Suddenly, a smoke came off from the L4 component on 6HC in the picture. After turning everything off and looking for errors, 6HC works fine like nothing happened.

    What function does this component have? Where should I expect an error to occur?

    I repeat, there seems to be no issues with 6HC




  • Guessing its a filter for the internal 5v supply

    how's the power arrangement for the pi?

  • administrators

    Looks like the 5V output was overloaded. It turned out that the overload protection of the 5V regulator that we use on the MB6HC isn't very good. The rated current of the regulator is 3.5A but the overload protection may not kick in until 6.5A. L4 is the component that fails or smokes first when excessive current is drawn from 5V.

    On the version 1.1 boards, we beefed up L4 and added a 3A PTC fuse.

    I suspect that you were powering too much from the 5v rail, for example a RPi 4B plus HDMI screen. Or perhaps you had a transient short circuit between +5V and ground.

  • @dc42 looking at the jumpers it looks the Duet Pi is externally powered? thats why I asked OP to confirm.

  • administrators

    @bearer said in Mistery smoke on 6HC:

    @dc42 looking at the jumpers it looks the Duet Pi is externally powered? thats why I asked OP to confirm.

    Good point!

    Maybe there was a short on or under one of the IO_n connectors or the DotStar/Neopixel connector, between +5V and ground?

  • The RPi was powered externally using a 5V power supply

    There is a high chance that I made a short circuit on the IO_n port. "Duet" to my jump scare everything was unplugged as soon as the smoke appeared before made a thorough inspection. My bad

    Everything works normally. What problems should I expect if L4 fails completely?

  • administrators

    I think it's unlikely that L4 will fail unless you get another short circuit, but if it does then the internal 5V regulator will just stop working.

  • @dc42 I'll keep an eye on it and try my best not to definitely fry my board this time

    Really happy with how you design this board. It has been a blast playing with them.

    Kudos to you and the Duet team!

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