Troubleshooting Hotend Temp Signal

[dc42]

It's most likely caused by a bad connection in the thermistor cable. A short between the thermistor connections and the hot end metalwork might also cause it.

[Hornetrider]

is a cable break always triggered with 2000?
If not, then a short should be the root.

It's just to find the problem a bit faster then removing all cables...

thx for supporting

[Cecil]

But short shouldn't give you 15°C, or it'll need to be shorted to very specific voltage. Short to GND should give high temperature. Will short to VIN survive?

[Hornetrider]

printing right now...

[dc42]

Like I said, bad thermistor connection or short to the hot end metalwork. Shorts to the metalwork were very common on E3D hot ends before they switched to cartridge thermistors.

[Hornetrider]

@dc42
this "old" thermistors, have they been small and with a thread?

I will change the hotend as soon the print is done and test accordingly.

Strange thing I noticed:
a test print with a 40x10x40 cube just before this print worked without trouble..same filament and settings...

Is there a way to log the temp with head position?

[Hornetrider]

@dc42
Hi

I have changed the thermistor and checked all the cables, but still experiencing the spikes.
The good thing it is only during print.

I am wondering if this might be linked to missing earth connection as the DUET is powered via 24VDC and without any earth/ground connection.

Is it advisable to connect the frame of the printer (its all metal..more or less) to the ground of the powersource?

Any further hints?

[Phaedrux]

@hornetrider said in Troubleshooting Hotend Temp Signal:

Is it advisable to connect the frame of the printer (its all metal..more or less) to the ground of the powersource?

Yes. Proper grounding is a matter of safety.

[Hornetrider]

check this out...

I have changed the thermistor, some prints like calibration cube work well.
But now even with heated Hot end performing a G32 or G29 I see the spikes.

I also tried the G29 with BED off and still bad signals and strange height map with pikes in it. Tried with a clean glas bed and still the same sh..

Next step, routing a spare cable for the thermistor and test, but I am quite sure this won't help.

Is there a possibility that the board loads some capacities?

[dc42]

If you suspect the Duet, try connecting your thermistor to E1_THERM instead of E0_THERM, and add parameter X2 to the M305 H1 command in config.g to tell the firmware you did that.

[Hornetrider]

UPDATE

Fault found.

As the temp signal was always spiking below the set-point I wasn't sure about the source. But a new 2000 spike brought me back on track...
In the end the cable from board to thermistor had a failure. Just connected a new on the fly and the signal was rock solid again.

I also connected the frame of the printer to Earth, this already lowered the spikes but it also brought me the 2000er..

So, in the end I also installed the BLTouch that I had in stock, now the mesh is also free of spikes...

Thank you all for your support.