Duet 3 Thermistors showing -273.1

  • Hello,
    On my new duet 3 board, all four thermistor inputs constantly show -273 °C when running reprapfirmware using the M105 command, regardless of the attached resistor.

    I Tried connecting

    • Short Circuit (0 Ohm)
    • 1k Resistor
    • 100k Resistor
    • 100k Thermistor
    • Open Circuit

    between the thermistor pins, with no success.

    Also my continuity tester beeped between VSSA and Endstop GND, so I think the VSSA fuse is fine.

    The rest of the board is working fine.
    Is this a hardware issue or can this happen by falsely configuring the firmware?

  • the only hardware explanation i can think of is if there is a short from the thermistors to VSSA, should be possible to measure when powered down.

    if there is no short, then odds are the configuration is wrong, but its also possible the ADC has failed but less common.

    post your config and/or do some measurements?

  • administrators

    1. Please share your config.g file.

    2. Check your config.g file by runnig M98 P"config.g" to see if you get any error messages.

    3. One cause of all thermistors reading -273 is that there is a short between VSSA and a higher voltage, for example a heater wire. Such shorts are quite common in 3D printers, which is why Duets are protected against them. So disconnect all thermistors from the Duet, then test using resistors again.

    4. If you still always get a reading of -273, check the resistance between VSSA and GND. It should be only a few ohms, it's the resistance of the VSSA polyfuse..

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