Bad Thermistor?

What can I do to confirm a thermistor is dead?

I've been getting this for days:

< 10:53:23 AM: Error:0
< 10:53:23 AM: : Extruder switched off. MINTEMP triggered !
< 10:53:23 AM: Errorrinter stopped due to errors. Fix the error and use M999 to restart. (Temperature is reset. Set it after restarting)

It doesn't seem to be the RAMPS (crossing the pins was able to raise the temp reading past 290+) or USB cable (tried another cable).

This is on an ABS printer that came fully assembled.

 

This usually means that the RAMPS board isn't getting a resistive reading from the thermistor. This means that somewhere there is a break in the wire connecting the thermistor to the board.

If you had the opposite where you had an insane reading though nothing was heated would mean you have a short. Typically, I believe, we've seen when a thermistor dies, you get a short not a break.

So check your wires. Disconnect the thermistor wires from the ramp and see if you can use an ohmmeter to find the break.

 

Did you ever get a multimeter?

 

I got the multimeter and checked the wire, it's getting resistance. Does that mean it's not broken?

If so, then does it mean the thermistor is bad?

 

Resistance is a good thing. It should be around 100k resistance at room temperature.

You have a loose wire somewhere between the thermistor and the ramps board

 

Isn't the wire from T0 connected straight to the thermistor?

 

yes and if it's reading 0 you're getting an open connection, which is probably from a loose wire

 

But it's not reading 0, it reads 118 or so, therefore it isn't a loose wire?

So I guess it is the thermistor?

 

Loose doesn't mean broken. It means intermittent. IE movement from the nozzle

118 doesn't really make sense. In your post it said: < 10:53:23 AM: : Extruder switched off. MINTEMP triggered ! which means that it hit below 5C.

I suppose a faulty thermistor *could* read 118 but that's very unlikely. Thermistors work by measuring the resistance change across dissimilar metals at varying temperatures. If you have a connection between the two metals you'll get the expected resistance. As the joint is secured in a glass bulb it is very unlikely these two metals would be improperly connected if they worked at all. You can verify by it should be around 100k resistance at 25C.

Generally when a thermistor fails 1 of 2 things happen. It shorts and it acts as if the resistance has fallen to a very low amount and the control board reads 5v and outputs a very high value, ~290-300+C. The second is it's an open circuit, which shows 0v on the control board. This is because as a thermistor reaches 0C it starts to enter a very steep temp vs resistance curve and you no longer have reliable readings. This is why they add a cut off of 5C since that's relatively stable.


Check your cables. If you can pull it apart, it'll wiggle loose during use.

 

Sorry I meant the resistance was reading 118k not 0. The thermistor of course reads 0.

I've been pulling on the cables quite hard and nothing is coming loose... everything seems very well connected. How many connections exactly am I supposed to be checking?

 

my extruder thermistor cable had 4 different soldering points along it. You might need to pull it out of the protective wrapping. Or just contact team robo and they can send you another but either way you'd need to take it out.

 

Why wouldn't it just be one continuous cable from T0 to the thermistor?

 

I took everything apart, I'm guessing at this point its just a bad component. This would explain why the printer inexplicably fixed itself one time after I got this error.

 

Hi Guys,
I was doing some changing in wire-up and I broke my E3d V5 thermistor, I found my old stock head and I took out that thermistor will it work? I would need to make the hole in the E3d block bigger to facilitate for the robo stock thermistor, will I be able to just drill the hole bigger?
And if everything is given the go a head I cannot remember what I have to change the thermistor settings back too as well.
Thanks guys.

 

Thanks Mark