No Power to Bed or Hot End, after VSSA fuse replacement?

  • I am running a Duet Wifi, with the latest firmware

    Some time ago, I accidentally created a short between the bed power wires and the bed thermistor. After that my bed heater and hotend stopped working, the VSSA fuse, labeled F1 was blown. I replaced it this morning and also installed a new bed probe (NPN NO inductive probe). Everything is working, motors, hotend fan, auto calibration, web interface etc, but there still is a problem with the heaters.

    The web interface shows a temperature around 40 degrees for the bed and the hotend, a bit high but not completely abnormal. I measured the resistance of the thermistors and they are both around 100kOhm. I measured the VSSA fuse and it seems fine, no open circuit.

    The problem I'm having is that both the bed and the hotend are not heating up. After a couple seconds I get the error, heater heating up much more slowly than expected.

    After checking, the heaters are just not getting power from the board.

    Is there another fuse that I'm missing? Or could something else be messed up after the short, blown trace and how would I check that?

    I really hope someone can help me out, I need this printer for production, so it's really frustrating that it has been down for so many days.


  • administrators

    Before you get the error message, do the LEDs on the Duet for the bed heater and/or the extruder heater illuminate?

  • Thank you for the quick reply. Both the bed and the extruder heater LED do not light up, when I try to heat them up.

    I just noticed that when I do Not connect the thermistors to the board, they both read around 40 degrees, at the web interface. When I plug them in, the value doesn't change. I don't think 40 degrees is the correct value, when there is nothing plugged in. So the board probably is not reading the thermistors but some other component of the board?

  • Oh and on my other printer, the led next to the usb port keeps lid, and on the broken printer it goes out after 0.5 sec when switching on the machine.

  • administrators

    It does sounds as though something else has been damaged besides the VSSA fuse. Possibly the ADC in the ATSAM4E chip. Is that chip getting hot?

  • Yes, not super hot, but it's definitely getting hot. If that means the chip is toast, I will probably have to order a new board, since I won't be able to replace the chip myself I think.

  • What is the exact part number of the ATSAM4E8E chip, or which one should I buy from the link below?

    I would like to try to replace the 8 dollar chip, before ordering a new 180 dollar board..

  • administrators

    The chip is the LQFP 144 pin version:

    ATSAM4E8EA-Axx the last digits refer to the packaging (tape/tray) and the temperature, both are interchangeable in this use.

    The second revision "B" chips should also work:
    ATSAM4E8EB-Axx however I don't believe we have had any through our supply chain yet so I have not tested them. Generally you would expect a few bug fixes but with something this complex the new revision could have introduced a new bug which is why I mention it.

  • administrators


    What is the exact part number of the ATSAM4E8E chip, or which one should I buy from the link below?

    I would like to try to replace the 8 dollar chip, before ordering a new 180 dollar board..

    Replacing a LFQP144 chip is tricky. If you are in the US then you could send a PM to forum user W3DRK who may be able to replace the chip for you.

  • Oke, thanks a lot for the quick help! I ordered 3 chips (for future mishaps ;p), some fine solder and a flux pen, so lets hope my first SMD adventure goes well. I will report back if the replacement was successful, or not..

  • administrators

    It's worth watching some YouTube videos on SMT rework before trying. It's easy to pull the copper traces off the board if you are not careful. As a minimum I recommend getting some good solder wick and flux if you don't already have it.

  • administrators

    I advise against attempting it unless you have the right equipment. Here's the technique I use to replace driver chips, and it should work with processor chips too. You will need:

    • Electric hotplate
    • Thermocouple temperature measuring device. I use the thermocouple attachment on my multimeter.
    • Hot air SMD desoldering tool with a square nozzle about the right size for the chip.
    • Vacuum pick up tool. Very cheap on eBay.
    • Fine tipped tweezers
    • No-clean flux pen
    • Isopropanol spray
    • Cotton buds
    • Fine-tipped soldering iron
    • Solder wick
    • Strips of corrugated cardboard covered in Kapton tape - probably not needed when replacing a processor

    Use the strips of Kapton-covered cardboard to mask Molex connectors and other sensitive parts near the chip to be replaced from the hot air. Place the board on the electric hotplate with the thermocouple probe underneath it and adjust the hotplate to get a reading of 100 to 120C on the thermocouple. Wait several minutes for the board to come up to temperature. This makes desoldering easier. Heat the chip with hot air at about 260 to 300C until you are quite sure that the solder has melted all round. Gently lift the chip off with the vacuum pickup tool. As Tony says, it is easy to lift the fine traces off the board if the solder is not completely molten all the way round.

    To fit the new chip, apply no-clean flux to the pads. Drop the chip on the pads, the right way round, using the vacuum pen. Nudge it with tweezers until it is perfectly aligned with the pads. Heat the chip with the hot air until the solder is molten again (about 20 seconds), then remove the hot air and gently press the chip down with the tweezers, taking care not to shift it sideways. Remove the hot air and turn the hotplate off. Allow to cool.

    Check under magnification that all the pins are soldered down and there are no bridges. Touch up any bad joints using the flux pen and fine tipped soldering iron, and remove any solder bridges using solder wick. Finally, use isopropanol spray and cotton buds to remove surplus flux.

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