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Hotend no longer reaching correct temperatures

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I've had my UM for about 1.5 years now. I'm very happy with it and I have used it a l lot. Lately I've been having problems with my hotend (after testing some conductive filament http://flashgamer.com/arduino/comments/conductive-abs-from-repraper) and I need some help.


My problem is that it seems that the extruder never reaches the temperature that is reported on my Ulticontroller. When the Ulticontroller says 220, I can barely extrude PLA by hand and ABS is impossible. When it reads 230, I can extrude a little PLA, but still no ABS. When I crank the extruder up to 260 (max) PLA flows fine but it's not fluid, and ABS is still super slow.


I've tried to measure the temperature on the aluminium block in two ways:

- using an IR meter

- using a cooking thermometer that goes up to 300 degrees (K Type Thermocouple)


When the Ulticontroller reads 260, these two will both report 185 degrees. I know that IR meters are known to be inaccurate, but when the thermocouple gives the same result and I'm having a hard time extruding all types of plastic, I feel that this the UM must be reporting this completely wrong.


My UM is upgraded with latest extruder + extruder drive and it's been running pretty much flawlessly for more than a year. Does anyone have suggestions as to where to start searching for errors? Do the UM thermocouple "fade" with age?


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a TC cannot really fade... I would take a look at the solder joints in the TC amp board on top of the head, and simply reflow them. then I would take a look at the output cable from the TC board to the UM board... maybe the pins on the connectors are corroded (and increasing the resistance, so you get only 1.85V instead of 2.2V on the pin)?


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Thanks for suggestions!

Today I finally had time to do some thorough testing. I tested all connections (no sign of corrosion), did a quick reflowing of the TC-board, tried a different cable and it's still the same.


Next, I found another temperature sensor based on a DS18B20. I taped both of these to my heated bed using Kapton, set 50 degrees and observed. Both my cooking thermometer, the DS18B20-based temperature sensor and the Thermistor beneath the HBP showed 50 degrees +/- 2 degrees. I then set 70 degrees and all three followed.


Next, I taped the two temperature sensors tightly onto each side of the aluminium block on the print head,wrapped it in aluminium foil to prevent any heat loss to the sides and did the same experiment. When the thermocouple reports 70 degrees, both the other two sensors report 50-51. When I set it to 100 degrees, the other two sensors report 68 and 72 degrees. The UM set to 125 returns 81 + 85 on the other two. If I point my IR thermometer up onto the aluminium block through a hole in the aluminium, it also reports the same temperature as the other two devices.


Between each measurement, I've let the temperature "set" for 5 minutes and the readings are very steady. I'm at a loss. Unless anybody has other good suggestions, I'll contact UM support tomorrow. Below is a picture of how I set this up for measuring.



PS: sorry about cross-posting to the Google group. I just want to get the printer up and do some long prints while the family is off on holidays :wink:



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Just thought I'd update this thread with the resolution in case others have similar problems. I was certain that it was the electronics, but after UM sent me a PCB to test with, I could conclude that different electronics didn't matter. Earlier tonight I stumbled onto the solution when changing the hotend to a brand new one.


Some months ago I experimented with conductive ABS:



This caused me to have to clean the nozzle maybe 20 times and during one of these "cleanings" I must have pulled on the Thermocouple cord rather than push it out through the aluminium block. This caused it to be slightly yanked out of it's metal casing. It still measured temperature fairly correct, but it reported it lower than it did when I now pushed it back nicely in it's metal housing.


The other part of my problem was that material didn't flow properly. I found this to be due to the white teflon part (above the PEEK) being damaged. I've taken the hotend apart so many times, but I never pulled out and checked this piece since it's not where the blockages occur. I had a spare one and with that in place, the printer now works nicely.


I hope this can help others with similar problems :)


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