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Solved Thermistor stopped working (again)

Discussion in 'Troubleshooting' started by 4sfaloth, May 23, 2020.

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  1. 4sfaloth

    4sfaloth Member

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    Hi all,

    A few weeks ago my thermistor stopped working and I ended up swapping it (if you want you can check that somewhat long thread here: http://community.robo3d.com/index.php?threads/cannot-release-hotend.23859/page-2)

    After that the printer resumed working fine, and I've been printing quite a bit. However, once again I'm having thermistor failures. The symptoms are pretty much the same as last time:
    1. All prints stop (not clog, the printer actually stops) after 5-20mins and through the serial interface I get this error message Recv: Error:Extruder switched off. Temperature fell too much during print!
    2. Sometimes when heating the extruder I see sudden jumps in temperature. For example just now I was heating it to 190ºC and when it was about 180º it suddenly jumped to 200ºC
    So again it seems like thermistor failure alright. Since the thermistor is quite new I thought it was just an assembly issue (yes, I don't trust myself with the hardware that much :p), that perhaps the thermistor was too loose against the hotend. But I verified quite the opposite: it seems to be really stuck inside and I am unable to remove it event after unscrewing the tiny screw that's supposed to keep it in place.

    So my questions are:
    1. Is a bad contact between extruder-hotend still the most likely explanation for this, or should I look into something else? I am really concerned that the new thermistor is failing in the exact same way as the previous, though as I said I wouldn't trust my assembly skills that much
    2. Any trick for removing the stuck thermistor from the hotend?
    Please let me know if any other information/photos/experiments can be useful in understanding this.

    Thanks in advance,
    Filipe Morais
     
  2. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    1) This error is in the FAQ :) Even if you replace the thermistor the reasons the firmware will raise this error are unchanged. The firmware saw temperature drop a fair amount so it raised that error and halted the printer

    http://community.robo3d.com/index.php?threads/faq-r1-r1-series-printers.19735/#post-119221

    2) That is probably also a contributing factor to the #1 above. It is probably jumping around because it is cracked or damaged. Thermsitors are tiny glass beads and don't suffer much damage or wear before failing. If you have an R1+ then it is encased in a metal canister (which helps) but it does not keep it from failing. Replace it.

    1) see above. The only other possibility is a bad connection in the wires that run back tot he RAMPS and there is at least one connector in the wiring harness if this is an R1+ ... that connection could be faulty.

    2) Heat it up (with that set screw loose or removed) ... to 240 or 250 C and gently push/pull that canister out.

    EDIT: I see from the pictures in the other thread that this is indeed an R1+
     
  3. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Check the insulation on the thermistor wires down near the hotend as well because if there is any bare wire exposed that can short out against the heater block and will give you crazy readings as well.
     
  4. 4sfaloth

    4sfaloth Member

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    Hi Mark,

    thanks for stepping in once again.

    1. Insulation seems fine
    2. Damaged thermistor is of course a possibility, but isn't it odd that it will fail after less than a month of use? The previous one lasted much much longer
    3. I saw in the FAQ that another possibility is the fan blowing over the thermistor. The fan is still the original one, so it hasn't been moved or misdirected so I guess it's fine. I did notice however, that when assembling this hotend that the thermistor and the other cable and coming off the front and slightly to the right, while with the previous one the cables were coming off almost 90º to the left. Is it possible that this makes it get more air from the fan, and thus fail more? That would explain why it fails after a few minutes, and not immediately. Is so, do you know if I can try to assemble the hotend in a different position, or if they only come up in a precise orientation?
    4. I did change a fan-related setting on the slicer recently (not sure if it was exactly before this issue). Basically I increased the height at which the fan would be turned on. I don't see how this could be related though
    Thanks in advance,
     
  5. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    I was afraid it was actually the thermistor, but hoping that it was just insulation missing or something simple :)

    If you think the fan is the culprit disable it. The parts fan is not required (but it does help a lot) and disabling it for a test will tell you if that is the problematic part. If it is then maybe consider a different fan mount that will redirect the airflow away from the nozzle/heater core better -- there are a lot of alternatives on thingiverse,

    Given your description of how it is behaving I would say it is NOT a defective thermistor (or not likely at least)

    There are a lot of variations on the GregsWade extruder that Robo used. However switching would mean being able to print one. Most of the ones you can buy preassembled are much the same as what Robo used. But there are a lot of different fan mounts so look at that...
     
  6. 4sfaloth

    4sfaloth Member

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    I tried to print with the fan disabled today but to no avail. So that's not the issue :\

    I was unable to remove the thermistor core from the hotend, even after heating it up to 240ºC. It really seems stuck in there...

    For now I just disconnected and reconnected all thermistor wires (there are two connectors before going 'inside' the printer) and I'm now trying to print again (but I'm not very optimistic about it :p)

    I am very close to blame it on thermistor failure and order a new one (even though this one only lasted <1 month!) but before that I just wanted to try and clarify something in my head. @mark tomlinson you said before
    . The only other possibility is a bad connection in the wires that run back tot he RAMPS and there is at least one connector in the wiring harness if this is an R1+ ... that connection could be faulty.

    but I'm wondering: wouldn't a faulty connection lead to 'binary' errors, that is, either it worked or not? Or could it also somehow cause the temperature spikes I've noticed (eg: jumping from 180º to 200º when trying to heat to 190º or something like that)
     
  7. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    A bad connector could either always cause an immediate failure or, if just loose/poor connection it could intermittently cause a failure.
    If you can't get the thermistor core out maybe just get an entire hotend so you can swap the new one in and then mess around with fixing the other one on the bench :) You could then disassemble it mist of the way and heat up the heater block in an oven and try to get the thermsitor can out.
     
  8. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    The type of connector that Robo used is not really what I would consider the best choice for that application.
    Deans connectors or Anderson Power Poles would be far more reliable.
     
  9. 4sfaloth

    4sfaloth Member

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    that's what I think I'll do... Thanks for the help
     
  10. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Best of luck.

    There is always a remote chance that the RAMPS or Arduino is failing, but I would consider that most unlikely.
    I mention it just to cover all the bases.
     
  11. 4sfaloth

    4sfaloth Member

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    I have some new information regarding this issue, though I'm not sure it changes anything in the end.

    After the last print failure I noticed the thermistor's copper tube (the part that sticks out of the hotend) was VERY close to the heating wires (the red ones); since that can get really hot I thought that perhaps was not a good thing and could be related to this. So I wrapped the thermistor and the heating wires separately using capton tape. After doing this I was able to successfully finish a 2h print. However, I got the same error 3h30min into another print. So it seems it helper, though not completely fixed

    Am I right in assuming that the thermistor's copper tube should not touch the heating wires? Perhaps the proper fix for this would be to somehow try to physically separate them a bit more?
     
  12. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    The tube is mounted to the heater block and that block is (effectively) ground.
     
  13. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    This video is an assembly of the hexagon. I think it is from before they switched to canister style thermistors, but other than that it is all the same. You don't want wires touching if you can avoid it

     
  14. 4sfaloth

    4sfaloth Member

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    I forgot to update this but in the end I had to replace the hotend (couldn't remove the previous thermistor from it, which I clearly overtightened and smashed, probably causing the issue in the first place). Thanks once again for all the help
     
    mark tomlinson likes this.
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