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Help - MK8 Extruder upgrade and now thermsistor problem
Hi gang. I'm finishing a changout of the extruder from my XYZ and while everything seems to function, the hotend thermsistor reads a constant 20 degrees C. At the same time I swapped out the extruder I also installed Repetier - which I'm less than comfortable with. Heating the hotend is no problem - I measured $280 degrees with a laser thermometer, when I shut the printer off to stop it. The screen still said it was 20C. I'm uncertain if I have a hardware issue or a problem with my Repetier configuration.

Any help appreciated.

I installed an MK8 extruder a couple of days ago. I have been using Repetier Host and Repetier firmware for some time now. My extruder came fully assembled with the heater and thermistor already installed. For me everything just worked. I did eliminate the extruder control board. I wired the thermistor to the black and yellow wires directly. The only thing the board adds to the thermister is a couple of filter capacitors, so I did put a 2.2 mfd cap between the two wires (cathode/GND/- to the yellow wire) but that was more for my benefit and I really doubt it will be required. I have not yet verified my temperatures are correct but the printer is working just fine. I hope that helps a little...
Thanks James. I'll try changing the one that came with my assembled extruded. I've never had a thermsistor sorta work before. They either were perfect or they didn't work at all.
Make sure your temps are correct with the thermistor you are using. For my mk9 I had to calculate the temp table in REP using the thermistor's Beta.
After a few days with the new hot end, I started having intermittent temperature problems too. My MK8 is a Chinese knock-off (printer was down and I was very low on funds.) The thermistor runs through the heater block, with one wire coming out each side rather than next to each other. The hole it is in however is about twice the size of the thermistor itself leading to poor physical contact between the two. The sleeve the wires are in appears to run all the way up to the actual part, so I used a small wire to pull a doubled over piece of copper braid (desoldering wick) through the hole along side the thermistor. Problem solved.
OK, nevermind. The copper braid worked for a day or so, long enough to print a mount for the E3D that I should have saved my pennies for in the first place. I knew I shouldn't cheep-out but I did anyway. Lesson learned (again.) The mount I printed looks great though!

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