I got my replacement thermistor from e3d’s site, because after a print fail, my old thermistor got torn in half. After wiring up the new thermistor I booted up Cura, and my temp read 129c. Which is what it was showing with the old thermistor when it was broken. I switched the heated bed thermistor with the hotend one and the temp then changed to 24c (room temp). I really doubt that the brand new thermistor is broken, so could this be a firmware thing? I ruled out a board problem because the error follows the sensor, not the port.
How about wiring between the hotend thermistor and the control board?
I’m leaning towards brand new thermistor being broken. Do you have a volt/ohmmeter? You should measure a short between the two tabs/wires. The tips are spotwelded together and because it’s two different metals it’s a very brittle weld: they may have broken apart.
I will test it when I get home. What kind of reading am I looking for?
@Alan_Thomason thanks the first thing I checked, the wires are perfectly intact and if it was broken I wouldnt get a reading at all.
You should see a resistance of around 100k ohms for the thermistor. I would disconnect it at the controller board and check from there - that way you eliminate the wiring at the same time and you see the actual value that the board sees. Also, while you have the ohm meter attached, tightly hold the thermistor between your fingers - you should see the resistance change as it heats up.
@Alan_Thomason Thanks! Will do.
@Alan_Thomason I’m getting a reading of only 1k ohms, but the meter is old so I may have to zero it
As far as I know, most thermistors are around 100k at room temp. You may have to verify that value with the printer manufacturer or if it has a part marking you may be able to find the specs online.
If re-zeroing doesn’t do it, try measuring at the thermistor. A reading of 1k at the board would either be a partial short in the wiring (very weird) or a defective thermistor (assuming 100k is the right value for this thermistor).
@Alan_Thomason yes 100k is the correct value. Im just going to use a electric one rather than my analog one
@Alan_Thomason ok so I zeroed the meter and am still only getting 10k ohms, does that mean I’m shorting somewhere?
Yeah, that would be a partial short. Can you check each wire separately? Or disconnect the thermistor and check it and then check the wires…
@Alan_Thomason ya I will test them now
@Alan_Thomason ok, so by completely bypassing the wires the thermistor reads 45k on the Rx1k setting but when I switch to the Rx100 setting, it reads only 14k, so I’m not really sure whats going on here
That’s really weird. Are you using a digital volt/ohm meter?
@Alan_Thomason its analog, so I could be reading it wrong but I don’t think so. I’ll show u some pics
@Alan_Thomason sorry I realized it had a loose connection, sorry.
How can I test the wires?
Jusr realized how stupid that question was xD
Confirmation: yes the wires are broken.