Pursa I3 MAXTEMP error

I've got Createc3d Prusa I3 with E3D Full Metal hotend.
Not sure, what thermistors were shipped with it and don't know, how to check it.
But, according to settings in Marlin firmware, it is 5 (ATC Semitec 104GT-2) for hotend and 1 (EPCOS 100k) for heatbed.
It was working fine for about 1,5 year now.
I'm printing with ABS.
My settings are:
hotend temp: 245 C
heatbed temp: 110 C for first 3 layers, than 70 C

Most relevant firmware settings are:

#define TEMP_SENSOR_0 1
#define TEMP_SENSOR_BED 1

#define HEATER_0_MINTEMP 5
#define BED_MINTEMP 5

#define HEATER_0_MAXTEMP 275
#define BED_MAXTEMP 150

#define  DEFAULT_Kp 26.22
#define  DEFAULT_Ki 3.08
#define  DEFAULT_Kd 55.84

#define ABS_PREHEAT_HOTEND_TEMP 245

Suddenly, during printing I faced MAXTEMP error.
After that, when trying to preheat, hotend temperature started to fluctuate.
So, I've decided to replace thermistor.
As soon, as I didn't had the same exact thermistor, I'd replaced it with spare for heatbed.
So, I've changed thermistor constant for hotend from 5 to 1, performed PID autotune, save results to firmware and flashed.
Now hotend temperature not fluctuating anymore, but I'm still getting MAXTEMP error during printing.
Resistance for both "damaged" and "working" thermistors is something around 100 KOhms.
Before and after MAXTEMP error new thermistor seemed to behave absolutely adequate.
Trying to exclude occasional shortcut between wires where thermestor meets hotend, but they are too close in thermistor body itself, so I wouldn't bet my arm on it.

How to debug the issue furthermore?

To ensure no shorting, get some silicone RTV, slide the insulation all the way up the thermistor leads, coat in a small dab of RTV, and let it set. Then, coat the tip of the thermistor again in RTV and set it into the hot end and let it set. it should stay insulated from ground and itself.

Did you inspect the thermistor socket on the controller for intermittent shortcuts?

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o_lampe
Did you inspect the thermistor socket on the controller for intermittent shortcuts?

Hi,

I have MINTEMP error and no clue until now for troubleshooting. How can I inspect socket for intermittent shortcuts?

Best Regards

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o_lampe
Did you inspect the thermistor socket on the controller for intermittent shortcuts?

Not yet. What am I supposed to do to check it?

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hoxsiew
To ensure no shorting, get some silicone RTV

Don't know, where to get that stuff in my country, but I hope I'd protected it well enough with dielectric varnish now.
So far printing, keeping my fingers crossed).

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yuzmemak

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o_lampe
Did you inspect the thermistor socket on the controller for intermittent shortcuts?

Hi,

I have MINTEMP error and no clue until now for troubleshooting. How can I inspect socket for intermittent shortcuts?

Best Regards

A MIN temp error is the opposite of a shortcut. Sometimes the thermistor legs aren't crimped very well to the wires. They often are soldered only, which can melt and desolder at higher extruder temps.

Actually, it works fine again. So, problem was in sudden shortcut where thermistor contacts hotend.
Now fixed with dielectric varnish.
Thanks for your advises.
Though, I still want to know how to check thermistor, or any other socket for internal shortcuts (just in case))

Get a Voltmeter with continuity checker. This makes sounds.
Clip one lead to the thermistor end and the other lead to a pin connected in the connector. Wiggle the wires at each side of the connections and listen for sound.

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