Hotend turns off randomly  

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jorik.o
(@jorik-o)
New Member

Hey,

I've had my printer (mk3) for about 3 weeks now. Produced some high quality prints so far, but now I start running into the same problem over and over again.
The bed heats up fine, but after some minutes of printing (or preheating) the temperature of the hotend starts dropping and at some point the Thermal Runaway error shows up.

I measured the output of the Einsy Rambo to the hotend and at some point it doesn't show any voltage anymore. From this point onward the temperature starts dropping and the thermal runaway error shows up as mentioned above.

Hope any of you have an idea.

edit: I measured the voltage of the 2 power lines coming out from the PSU towards the Einsy board. These are still 24v during and after the temperature drop, so I guess that rules out PSU problems.

Posted : 25/08/2018 12:34 am
MrMik
(@mrmik)
Honorable Member

Where did you measure the EINSY output voltage?

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Posted : 25/08/2018 2:27 pm
charles.h13
(@charles-h13)
Noble Member

Could there be a broken wire?

Posted : 25/08/2018 2:40 pm
jorik.o
(@jorik-o)
New Member


Where did you measure the EINSY output voltage?

I stuck some jumper cables in the plug of the cables running to the hotend.

Posted : 25/08/2018 3:50 pm
jorik.o
(@jorik-o)
New Member


Could there be a broken wire?

I measured the output voltage of the Einsy to the hotend at the board, so it wouldn't be a broken wire from the board towards the hotend.

I looked at the 2 power lines coming in from the PSU and they keep providing 24 v even during the power cut

Posted : 25/08/2018 3:54 pm
MrMik
(@mrmik)
Honorable Member



Where did you measure the EINSY output voltage?

I stuck some jumper cables in the plug of the cables running to the hotend.

So it's not a broken cable to the heater.
I don't understand the software or electronics, but while you are waiting for more informed members to chime in, here is what i think:

There could be at least 2 causes:
1) The electronics want to supply power, but cannot (some electronic component failure)
2) The electronic think they need to turn off power to the heater element when they should not.
3) The electronics think they should turn off the power and they actually should (safety shutdown).

For scenario 2, a broken heat sensor or sensor cable could be the cause. You can diagnose this further by watching the nozzle temperature displayed on the LCD, before and especially during the failure.

Take not of the temperature fluctuations: If they are gradual and small, going just 1-2degC above and below the target temperature, that's good.
A broken temp sensor cable will be making intermittent contact and function apparently normally, until the z-height reaches the point where the contact becomes intermittent, usually worse at some x-axis point compared to another. This will then cause rapid and obviously erratic temperature display fluctuations, e.g. the displayed temperature drops or rises at an impossible rate, 10, 20, 30 or more degC from one second to the next.
As the x-axis movement bring the cable ends temporarily together again, the actual temperature is displayed again. It may then be a few degC too high or too low, because the heater was turned on or off while wrong information was being fed to the electronics. When the x-position comes to the cable break position again, it begins to jump erratically again. Eventually the (incorrectly reported) temperature remains too low for too long, and the algorithm concludes that there is a serious problem and turns off power to the heater element.

...
Posted : 25/08/2018 11:46 pm
jorik.o
(@jorik-o)
New Member



So it's not a broken cable to the heater.
I don't understand the software or electronics, but while you are waiting for more informed members to chime in, here is what i think:

There could be at least 2 causes:
1) The electronics want to supply power, but cannot (some electronic component failure)
2) The electronic think they need to turn off power to the heater element when they should not.
3) The electronics think they should turn off the power and they actually should (safety shutdown).

For scenario 2, a broken heat sensor or sensor cable could be the cause. You can diagnose this further by watching the nozzle temperature displayed on the LCD, before and especially during the failure.

Take not of the temperature fluctuations: If they are gradual and small, going just 1-2degC above and below the target temperature, that's good.
A broken temp sensor cable will be making intermittent contact and function apparently normally, until the z-height reaches the point where the contact becomes intermittent, usually worse at some x-axis point compared to another. This will then cause rapid and obviously erratic temperature display fluctuations, e.g. the displayed temperature drops or rises at an impossible rate, 10, 20, 30 or more degC from one second to the next.
As the x-axis movement bring the cable ends temporarily together again, the actual temperature is displayed again. It may then be a few degC too high or too low, because the heater was turned on or off while wrong information was being fed to the electronics. When the x-position comes to the cable break position again, it begins to jump erratically again. Eventually the (incorrectly reported) temperature remains too low for too long, and the algorithm concludes that there is a serious problem and turns off power to the heater element.

Firstly, thanks for thinking with me 🙂

The heat sensor of the hotend seems to be working fine, the fluctuations are small (the problem also occurs when the printer is in preheat mode, without the motor and thus cables moving). The power coming from the Einsy shuts of first, causing the temperature to drop.

The causes that you descriped could be it indeed. I just have no clue how to test them to rule them away/confirm them.

I contacted customer support as well, they also didn't really know what the problem could be.
They are going to send me a new heating element, although I doubt that this will solve it.

Not really sure how to proceed now :/

Posted : 26/08/2018 10:32 pm
MrMik
(@mrmik)
Honorable Member

A new heater element will not fix the problem.

I would probably avoid taking the entire cable bundle apart to prove that, and just plug the new heater into the Einsy and into the extruder, but leave the printer otherwise assembled. If it turns out that the new heater does fix the problem, then you have not wasted any great amount of time establishing that.

I don't think you can safely test the new heater without installing it in the extruder, but it's cable can be left loose just for the testing.

I think you will need a new Einsy.

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Posted : 27/08/2018 12:08 am
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