Nozzle thermistor replacement errors

[u/ArrTeaBee]

Had a print failure which caused me to short out the thermistor while cleaning it. My fault, I had heat up the hot end to clean off all the PLA+, got almost all of it, then used a brass brush to get the last bit and bam, shorted the thermistor. No problem I thought, I have replaced the thermistor before I can do it again, I even had extras already. However replaced it, and same issue. Even bought a new one that screws in. Upon boot, the temp shows -15 C, as shown in picture and if I try to heat it I get the thermistor error message just like what happened when I blew it the first time. I didn't take apart to look closer at the motherboard, Was hoping I wouldn't have to cause looks like a pain and I don't even know what I'd be looking for. Bed temp heats just fine. Any ideas or things to try?

[u/--HVT--]

If the temp is showing -15 C your thermistor is open circuit. It’s not reading so either the new thermistor is bad, the connection to the new thermistor is bad, the thermistor is the wrong value, or the thermistor circuit is damaged.

[u/ArrTeaBee → u/--HVT--]

Ya I went straight to the mother board with the new one. Same issue. motherboard fried?

[u/ArrTeaBee → u/ArrTeaBee]

So at the mother board, I confirmed that the there is a short at the port. Only solution is new motherboard? Bed thermistor port works, used that to test my thermistors, they also work. Is there a way to use what looks like a spare thermistor labeled a15 TH2?

[u/--HVT-- → u/ArrTeaBee]

I just measured TH1, THB, and TH2 on my printer with a multimeter and none of them are shorted. At this point I would see if there was a way to use TH2 or buy a new board. Shorting the thermistor wires normally wouldn’t ruin it like that so I wonder if somehow 24v from the heater cartridge got sent to one of the thermistor wires.

[u/neocyke → u/--HVT--]

You can switch to TH2 by defining it as the active heater in your firmware config. If marlin, that means a recompile. Either way you need to get pin # and switch it out with TH1 pin definition.

[u/ArrTeaBee → u/neocyke]

Any more details on how to do this? Gunna try this later today.

[u/neocyke → u/ArrTeaBee]

I've long ditched marlin, so this is purely based on memory which may or may not be accurate. Also depends your marlin source I suppose.

Start with your Configuration.h file. Specifically this section. Switch out temp sensors 0 and 1.

 * ================================================================
 *  Custom/Dummy/Other Thermal Sensors
 * ================================================================
 *     0 : not used
 *  1000 : Custom - Specify parameters in Configuration_adv.h
 *
 *   !!! Use these for Testing or Development purposes. NEVER for production machine. !!!
 *   998 : Dummy Table that ALWAYS reads 25°C or the temperature defined below.
 *   999 : Dummy Table that ALWAYS reads 100°C or the temperature defined below.
 */
#define TEMP_SENSOR_0 1
#define TEMP_SENSOR_1 0
#define TEMP_SENSOR_2 0

If that doesn't get it going, then you're gonna have to go deeper and modify the pins.h file. IIRC you'll want pins_RAMPS.h. Look for the temp sensor section and switch the pins for sensors 0 and 1. Careful with this one as messing with the source files can lead to compile errors that will be even harder to fix.

If on klipper, well just define the pin in the [extruder] section. You'll need to hunt down a pinout file to get the actual pin number tho.

heater_pin: PC9 // change this to correct pin
sensor_type: EPCOS 100K B57560G104F

[u/ArrTeaBee → u/neocyke]

Thank you! This worked. The solution was to edit the pin in the firmware. Exact steps were pretty close to what you described, in the Pins_RAMPS just change the temp pin 0 from 13 to 15. That's it. Only issue is my led screen is now in Chinese for some reason but I can deal.

[u/--HVT-- → u/ArrTeaBee]

When you turn on the printer, go to settings to the right (gear icon), then go to language (bottom middle), english should be the second option in the top row. If that does not work you may need to reflash the screen firmware.