Solved Extruder Thermistor Fail (née: Heated Bed Failure)

I am well within my warranty, I will start that now. I got the firmware updated, it's saying I've still got a target temp of 210 (PLA)
I've got it running another test print from the sd card and it's hovering around 199 and going strong. I'll give that a minute and see.

 

Ok, I've got a parts request started, firmware updated, I do have a multimeter (didn't think I did) but I don't know how to actually check the resistance, as I've never used it before.


do I need to have it turned to a specific setting? And which connection am I touching it to, the one coming directly from the hot end, or the thermistor itself that unhooks from that?

*Edit - Alright, test print is done, and good! Looks like it's working, though the hovering around 199 concerns me a bit.

 

If it can't get to 210 then the thermistor is loose and not making good contact with the metal.

 

ok, I turned everything off, I set the multimeter to 200k ohms (the horseshoe-like symbol right?)
Tested the connector coming off the machine itself and the meter read about 5.5
Tested the thermistor and it reads 76.0 - 77.2

 

in the 70kohm range is fine if it's warm. 100kohm is for ambient temperatures.

Just gotta follow all the connection points and try and make it trip. It's frustrating to troubleshoot but eventually you'll find the smoking gun

 

Alright, moved it around a bit, getting the same reading (I take it I am using the measurement from the connection coming directly off the machine?

And since I am getting the same 5.5 reading, what does it mean that it's not tight against the heater block, that the bead isn't in a good spot on the hot end? Or that it's something to do with the wiring?\


*Edit - ok, it sounds like I am measuring from the connection on the thermistor itself, I checked that again and I'm up to about 83.1ish and rising



Ok, just remeasured and then measured at the point where the wires are soldered to the thermistor, both are fluctuating around 79.~

*Edit - pulled the boot off again, this where where the thermistor is currently sitting, it's kinda stuck actually, I don't know how much it matters where it is touching the extruder or what not or if there is a specific spot it needs to be.


There is still some leftover PLA around the extruder itself, thin bits and pieces.

 

that's really not a good spot for the thermistor. It needs to be in the hole for it.

 

Alright, and which hole is the thermistors?
I've got the big hole the heater core wires go into
the small hole to the left of it

and another small hole on the side to the right of that.

 

Alright, gonna heat it up so I can melt the PLA on the extruder and wipe it off a bit, but it is hole #2 here then?

 

that's the rubber boot but yes it does go in the hole adjacent to number 2

 

And I just push the bead end of the thermistor into the hole and put the boot back on?

like so:


I got it into hole 3 here but it keeps jumping out when I try to get the boot back on.
Hole 2 is too small, I had difficultly trying to get it in there and I was afraid I might break it.

 

nope you're not understanding.

It doesn't need to go through the boot holes at all, you can just use the boot to kinda press in on the thermistor wires from the side

Watch this, the most important part is that the thermistor is making good contact with the metal inside the hole. As you're actually measuring the internal temperature of the metal instead of the colder exterior.

 

Ok, I think I've got it. Though I did manage to get it in the hole of the boot as well, running another test print now.

Ok, looks like we got the same thing, it starts alright and then kicks out after a few minutes

 

it's probably a connection somewhere. Check the ramps board underneath

 

Nothing appears to be loose on the board, Except for the fan that covers the board on the bottom cover I'm comparing it to the diagram from the first page of this thread.

Pretty much disconnected and re-connected every cable on the board I can find

Put everything back together, and running another test print

*Edit - Same issue the extruder temperature falls after a few minutes

 

Try printing from a software like repetier host. Watch the temperature curve during a print and see if it's more of a gradual drop off or if it's a sudden spike