Thermocouple board faults on power up



  • This is on a Raise3D N2+ printer. Duet2 WIFI board. PT100 board and Themocouple board.

    Extruders on this printer have TypeK thermocouples. I put a PT100 sensor on the bed.

    I am using shielded, twisted, typeK thermocouple lead to run from the print head to the Duet board. Over 2M of wire required to make the connection. The drain lead from the shields is connected to a vacant ground terminal on an Extruder endstop connector.

    The issue I'm having is that when I power up the machine the thermocouple board will fault with red LEDs illuminated. If I touch the bare header pins on the top of the board with my finger the fault clears and I can then print without issue. Over the past week i ran 25+ print jobs for over 100 hours of printing without issue.

    When I was done with that batch of work, I powered the machine down briefly and switched it back on - the thermocouple board did not fault. I left it powered down for several hours and when i powered up one channel faulted. When I touched the pins the error cleared.

    As a shot in the dark, I took some slightly conductive foam and stuck it on the exposed pins on the board thinking that maybe the resistance of my fingertip was clearing the fault. That does not clear or eliminate the fault, but if I touch the foam with my finger the fault clears.

    If the board was easy to access, having to touch it on startup wouldn't be a big deal - but it's on the back side of the machine under a screwed-on cover, so access is not easy.

    I found a post that suggested putting .01 uf capacitors between the thermocouple pins and ground to improve noise rejection. Did that, it did not resolve the issue.

    Any suggestions on what to try to either resolve the issue or help identify root cause?



  • How hard are you touching the pins?

    It sounds like it might be an intermittent bad connection.



  • The slightest touch. I discovered this by accident when checking to make sure the board was seated.

    It seems to be between the first pair of pins inboard on the side of that connection and the center pair (don't know if it's one or both pins in either case).

    I took the daughterboard stack apart and joined the two board with a short 10 pin extension and that did not impact the behavior.

    I have carefully reseated the board without touching those pins - that had no effect. The fault clears immediately with a finger on the pins.


  • Moderator

    How do the pins on the Duet look?



  • @Phaedrux said in Thermocouple board faults on power up:

    How do the pins on the Duet look?

    They look fine, and there's no issue with the PT100 board under the thermocouple board - and again, I printed multiple jobs for for 100 hours of print time without issue once clearing the fault by touching the pins.


  • Moderator

    From DC42: "The 2x10 sockets on the underside of the daughter boards are hand soldered from the top of the board, so I would check first that all 10 of those pins are soldered on both daughter boards."



  • @Phaedrux said in Thermocouple board faults on power up:

    From DC42: "The 2x10 sockets on the underside of the daughter boards are hand soldered from the top of the board, so I would check first that all 10 of those pins are soldered on both daughter boards."

    Looked those over under magnification. No sign of a bad solder connection. Reflowed them all just because I could. No change.

    This is printer #2. Printer #1 is wired with the TC board on the print head and a long 10-pin extension (2m) between the PT100 board and the TC board. It has been working fine. I'll swap the TC boards when I have the time and see how that turns out.


  • administrators

    If you re-send the M305 or M308 commands that configure the thermocouples, does it clear the fault?

    Have you connected PSU negative output to mains ground? Is not then there could be a transient when you apply power, which could put the thermocouple interface chips into the fault state.

    Are you certain that you have a good connection between the shield of the thermocouple cable and Duet ground?



  • @dc42 said in Thermocouple board faults on power up:

    If you re-send the M305 or M308 commands that configure the thermocouples, does it clear the fault? ...

    Apologies for the lack of response. I've changed my profile so hopefully I'll get notification of replies.

    I will try your suggestions next time I have some time to kill. I tried swapping the TC boards between the two machines. The issue did not follow the boards. On the subject machine, the thermocouple of extruder 0 quit faulting. I tried replacing the TC in EXT1, but now it's worse and the fault doesn't clear when I touch the pins. The connection arrangement I have with the TC extension is a pain, so I'll have to double check what I did there.

    For now I have simply disabled EXT1, as I only run single-extruder prints. I would like to have it working at 100% though, so I will continue to try to get it solved. Thanks for your input.


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