Thermistor not working...

I have a Printrboard running Marlin that has been working great until today. I was "fiddling" with the j-head and upong reconnecting everything the thermistor read 218.36C. Unplugging the thermistor resulted in no change so it is obviously the board. The Temp is not always the same and can change up to 1C while I watch it but that is it.

I assume I shorted something out but how do I find out what? What can be fixed and what cant? I checked the resistance of the pins and both the heat bed and extruder thermistor read 0 ohms even though the Heat bed thermistor works fine. If it is unfix-able, can I route the ext therm pins elsewhere?

Quote

I checked the resistance of the pins and both the heat bed and extruder thermistor read 0 ohms

So both are shorted. BTW., did you unplug the thermistor while measuring? Measuring the resistance of the ATmega pin isn't helpful.

Quote

even though the Heat bed thermistor works fine.

Not possible. Perhaps your insulation is weak enough to short only when doing measurements with the meter, but a shorted thermistor gives always a very high temperature readout.

---

Generation 7 Electronics	Teacup Firmware	RepRap DIY

Your RAMPS might be fine. I've also noticed with an older version of the Marlin firmware on my RAMPS 1.2 that it didn't update the nozzle temperature when I disconnected the thermistor. But it worked fine after I plugged the thermistor back in, restarted Pronterface and reset the board. I didn't look in the code, but I assumed that the fw might not be updating the T reading or returning an M105 response when it senses that the thermistor has been disconnected (very high resistance).

Traumflug Wrote:
-------------------------------------------------------
> I checked the resistance of the pins and both the
> heat bed and extruder thermistor read 0 ohms
>
> So both are shorted. BTW., did you unplug the
> thermistor while measuring? Measuring the
> resistance of the ATmega pin isn't helpful.
>
> even though the Heat bed thermistor works fine.
>
> Not possible. Perhaps your insulation is weak
> enough to short only when doing measurements with
> the meter, but a shorted thermistor gives always a
> very high temperature readout.

To be honest I'm a hazard to everyone around me when I get my hands on a multimeter so lets just say I measured the pins incorrectly because the heat bed thermistor works fine. The extruder thermistor reads the same (around 220C) whether plugged in or unplugged so this means firmware or a component on the Printrboard is damaged. I am away from the printer for a week so cant upload fresh firmware but could it really go from fine to not for no reason? Alternatively if it is a damaged component maybe it is something I can replace or bypass?

brnrd Wrote:
-------------------------------------------------------
> Your RAMPS might be fine. I've also noticed with
> an older version of the Marlin firmware on my
> RAMPS 1.2 that it didn't update the nozzle
> temperature when I disconnected the thermistor.
> But it worked fine after I plugged the thermistor
> back in, restarted Pronterface and reset the
> board. I didn't look in the code, but I assumed
> that the fw might not be updating the T reading or
> returning an M105 response when it senses that the
> thermistor has been disconnected (very high
> resistance).

It's a Printrboard so no RAMPS and I have reset, disconnected and turned off numerous times with no change.

Everything is fixable, I just dont have the knowledge, hopefully someone else does...

Should the hot-end-temp analog input be rendered unavailable, there are other analog inputs on the printrboard, although it's unclear to me as a newbie whether they can be used easily by hacking the board and modding the code to address them instead of the original channels, or whether there would be associated damage to other analog inputs that makes them unusable.

In any case, the additional analog inputs are located on one of the "extension" ports. JP2 I believe, inputs A2 and A3 are unassigned, so they *should be available if they're still working and this issue doesn't self-resolve. See the printrboard schematic for more info.

Thanks, I am having a look at the schematics but to be honest I am not sure what I am doing and once I find a suitable input I am not entirely sure how to change the firmware (Marlin) accordingly. If someone can provide further insight, that would be great. For your convinience, here is the schematic.

look at the at90usb chip. this is the i/o chip and the brains for the board. there are some adc pins pf4-pf7


in ardunio language the actual pins are assigned differently. I'll look if no one else posts them by tonight.

Thanks, I have had a look in pins.h and again at the schematic and have come to the conclusion that I have no idea what I am doing.

Even once I decide (for example) I will use pf4 and even if I knew how to assign that pin to the thermistor in Arduino I still wouldnt know where to plug the thermistor because it has its own mini circuit. This is way out of my league, I will need detailed instructions to get it right. Is it even possible?

Did you ever get a solution for this?

I also was working fine until today. Suddenly I can not get the
hotend thermistor to read a temp.

It reads a constant 246.56C.
The thermistor reads fine when plugged into the heated bed circuit
on the board.

Trying to find out where to trouble shoot this
on the board.

Will it be easier to just replace the board?

So in my case the problem was one of the ADC pins failed.

hello, i have a taurino power with rams 1.4 and all connected to 24v, but now the thermistor of the bed says always 80ºc, i switch the taurino for one ardunio that a have for replacement and all works right.
can i switch the pins in taurino and ramps to get the thermistors works in other pins that be unsused

thanks a lot and sorry for the inglish