Print failure after hot end randomly drops temperature

[quartz tangle]

My Voron 2.4 had been functioning fine for 3+ years but recently started having issues with hot end temperature stability. Sometimes the hot end temperature suddenly nose dives and automatically cancels the print job. This temperature drop does not seem to be correlated with the set temperature or flow rate. Out of the 4 calibration cubes I've printed since this problem started, 2 encountered failures due to the temperature dropping.

Any ideas of what could be causing it? I'm suspecting my hot end is showing its age and needs replacement.

Edit: Forgot to mention I'm running the Afterburner extruder.

[tiny radish]

What hot end and thermistor

[quartz tangle]

I don't have the part numbers anymore but it is from the formbot aliexpress kit.

[tiny radish]

Got spare thermistor or heater

[modern cloud]

did you run PID autotune? https://www.obico.io/blog/klipper-pid-tuning/

[sudden yacht]

Does it consistently drop at the same time, or does it appear random? I would suspect a wiring issue.

[fallen laurel]

That looks just like what would happen if the heater is glitching out from some kind of bad wiring and just stops heating. If it had been the thermistor, it would probably jump straight to some crazy cold temperature (-47°C or something thereabouts).

[floral cliff]

A lot of times it seems like bad thermistor readings is down to a bad connection. Fixing that would be low cost. So that points to inspecting the connections for a high chance of a fix at low cost! That'd be my first step in troubleshooting!

[fallen laurel]

It could be a bad thermistor connection somewhere, but short of the thermistor falling out of the heating block (cooling it down too much), I think it would take something rather special to make it behave like that (it tends to be a lot more "jumping around").

[quartz tangle]

Nope. It drops randomly. Sometimes near the beginning of the print while other times not at all.

[quartz tangle]

I ran it a while back when I assembled the printer. It hasn't encountered any issues until this started happening so I haven't retuned it. I might as well give it a shot but nothing should've changed to make the PID coefficients untuned.

[quartz tangle]

I just bought a replacement heater. If that doesn't fix it then I'll assume it's the thermistor. If the thermistor replacement doesn't work then I'm all out of ideas.

[prisma rampart]

I am dealing with the exact same issue. I replaced the thermistor, then I replaced the small board on the head, then replaced the connector.. yesterday, I flipped the printer to side and connected the head to the board directly, it was reading room temperature but when connected thruoug the wires it was readin 125 degrees. I was certain that it was the wiring, so I've put new wires today. and it still read 125 degrees. at this point, I am suspicous of the board not supplying enough power to the thermistor to measure the ressistance value. I am plannig to move the thermistor to the other mcu. I am not sure if it can be done just through the config or not.

[floral cliff]

A thermistor doesn't require a lot of power. A thermistor changes it's resistance as the temperature changes. Yes, it flows some mA worth of current, but not 100's of mA.

[quartz tangle]

You mention a "small board on the head". I assuming you are using a CAN bus mod? I'm not using that in my case (though I wish I were). I'm no expert but a false elevated temperature means that either the thermistors resistance has somehow decreased, the power supply to the thermistor/CAN board is wrong, or something is wrong with the config.

The easy tests I can think of are to double check that you're configuring the correct thermistor. Check the "sensor_type" under "[extruder]" in your printer.cfg (though CAN bus may be different idk). You could check if the tool head board is receiving the correct voltage (Probably 24V) by using a multimeter. Lastly, if you have any 100K ohm thru hole resistors lying around, you could plug it in to the toolheads thermistor input and see what temp it reads. Using the measured temperature, you can refer to the thermistors datasheet equation and see if the ADC in the toolhead is working.

[prisma rampart]

it is not can board. it is those older boards that makes the connections tidy.

as for the config, the thermistor is set up correctly. I printed with both types of thermistors. the old one was a T-D500 and the new one is PT-1000, I was successfully printing with those thermistors and configs. This issue is just like the op's experience, it was intermittent it gradually got worse. The wiring originally is teflon sleeves, the new wires I added are silicon sleeve.

[prisma rampart]

Hartk Afterburner Toolhead PCB

[fallen laurel]

if it reads a constant incorrect value like that it doesn't seem likely with a regular wiring issue (which usually means it loses connection and reads very very cold until klipper freaks out and shuts down). Might be something else is connected in parallel with it (across the two wires) causing a lower resistance than it should have.