Hotend Thermister Issues

Which thermmistor type is on the machine now? The default is a type 1 (set in the firmware) if you switch to another type you must switch the firmware to match. Look here under thermal settings: https://marlinfw.org/docs/configuration/configuration.html

They are not all the same. Stock is:

1 : 100k thermistor - best choice for EPCOS 100k (4.7k pullup)

E3D is :

5 : 100K thermistor - ATC Semitec 104GT-2 (Used in ParCan & J-Head) (4.7k pullup)

Others? <shrug> you tell us not all printer 100k thermistors are the same. The firmware has to know this to know how to read the temperature accurately. Generally getting this wrong will just mean the reading is not accurate. Yours is pretty far off...

EPCOS and Semitec are only two of the possible types. That list in the firmware is pretty long...

* 0 : not used
* 1 : 100k thermistor - best choice for EPCOS 100k (4.7k pullup)
* 2 : 200k thermistor - ATC Semitec 204GT-2 (4.7k pullup)
* 3 : Mendel-parts thermistor (4.7k pullup)
* 4 : 10k thermistor !! do not use it for a hotend. It gives bad resolution at high temp. !!
* 5 : 100K thermistor - ATC Semitec 104GT-2 (Used in ParCan & J-Head) (4.7k pullup)
* 6 : 100k EPCOS - Not as accurate as table 1 (created using a fluke thermocouple) (4.7k pullup)
* 7 : 100k Honeywell thermistor 135-104LAG-J01 (4.7k pullup)
* 71 : 100k Honeywell thermistor 135-104LAF-J01 (4.7k pullup)
* 8 : 100k 0603 SMD Vishay NTCS0603E3104FXT (4.7k pullup)
* 9 : 100k GE Sensing AL03006-58.2K-97-G1 (4.7k pullup)
* 10 : 100k RS thermistor 198-961 (4.7k pullup)
* 11 : 100k beta 3950 1% thermistor (4.7k pullup)
* 12 : 100k 0603 SMD Vishay NTCS0603E3104FXT (4.7k pullup) (calibrated for Makibox hot bed)
* 13 : 100k Hisens 3950 1% up to 300°C for hotend "Simple ONE " & "Hotend "All In ONE"
* 20 : the PT100 circuit found in the Ultimainboard V2.x
* 60 : 100k Maker's Tool Works Kapton Bed Thermistor beta=3950
* 66 : 4.7M High Temperature thermistor from Dyze Design
* 70 : the 100K thermistor found in the bq Hephestos 2
* 75 : 100k Generic Silicon Heat Pad with NTC 100K MGB18-104F39050L32 thermistor

 

A "out in left-field" thought... I would check the thermistor and it's tiny connector. In my case, I had a thermistor which the wire at the connector was not secured to the pin - a poor connection. i.e. the wire was touching the pin and came out of the connector when tugged slightly. I purchased another from partsbuilt.com to replace it. Since they are the selected vendor for Robo parts, the received thermistor was the correct replacement.

Also, have you tried the PID Calibration wizard?

And... it might be a problem on the main board. I am sure that you have already done this action - checking that the connectors are plugged into the correct places on the main board.

 

Odds are good that it is the same type as stock, other than that @tkoco has covered all the bases.

 

That is useful. The Robo uses a 100kohm, NTC thermistor.

So nominally 100k and as temperature goes up -- resistance goes down (NTC - negative temperature coefficient) so if it is reading zero ... there is likely a open circuit in the wiring*. Alternatively the control board is bad. I'd sanity check the wiring first



*max resistance -> minimum temperature and the opposite is true, min resistance would be Max temp.

 

If you have a multimeter try reading the resistance across the thermistor (with ALL power off/removed of course)

 

We have different definitions of "works" then
So you are still stuck with either a bad connection/wire (adding resistance which would make it read low) or a bad control board.
I would still suggest you inspect each and every connector between the control board and the hotend (there are several).

 

Good idea

The issue is that once the cable gets from the control board to the extruder chassis (what we call the UpTown board) there are a number of internal connections inside that chassis before it gets to the hotend. There are at least two other connections it goes through that are effectively buried inside the extruder carriage. I found that all out the hard way when I added a second extruder to my c2 They did not even include the internal wiring for a second extruder on the C2 (because what idiot would add a second one?) So it is not as simple as a wire from the control board to the hotend. There are some small JST connectors internal to the extruder carriage and they are not a lot of fun to get to.

 

it is a nice piece of engineering, but not a lot of fun to work on

If you are curious you can see some of it in my thread for that: http://community.robo3d.com/index.php?threads/dual-extrusion-mod-for-c2.17686/

I documented it all in pictures... you can see the interconnects ...
The C2 and R2 use the same extruder chassis

 

I'd try a different thermistor to rule out a possibly defective unit. After changing the thermistor and a setting of 100 C still gives you a true temperature of 200 - 210 C, I'd try a different main board (assuming that you could get one).

Try not to make assumptions about what parts are good without testing - this includes ribbon cables and such. Simple things like a bad pin connection can trip you up.

 

See what it reads with the thermistor completely disconnected. That can tell you if it is the wiring.
Disconnect the wire from the control board and read resistance back to the hotend with the thermistor disconnected/removed. Should be open-circuit, if not then you have a wiring problem. I will say it sound like that at this point...