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I have a "classic" home built 3D printer, Arduino Mega, RAMPS 1.4 with Marlin 2.0.

It worked, was put in storage, and now I am trying to get it running again.

During all of the testing phases, the PID autotune, etc., the temperature of the hotend is stable.

When printing, for a few layers (4-5), the temperature is OK, despite the part fan coming on and off. However, after 3-4 mm of printing the temperature just rises and rises and rises, and after 275 °C thermal protection kicks in...

MOSFETs have additional cooling and a fan over them.

I'm out of ideas... Help!!!

My config files and G-code are here

Using PrusaSlicer.

Why do I see a temperature rise on the display? Last time I unplugged the printer and left it on USB power then gave it power again. During USB power temperature was steadily going down, as soon I plugged the main cable it resumed printing and the temperature rising again.

I did another test. 20mm above bed started printing, and got same result. I captured on video entire process Hot end to orbit. Around 2 min 30 sec the show begins.

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    $\begingroup$ Can you post a link to the gcode you were printing as well? $\endgroup$
    – Zeiss Ikon
    Jul 13, 2021 at 18:14
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    $\begingroup$ G code added to git. $\endgroup$
    – HerGiz
    Jul 13, 2021 at 19:31
  • $\begingroup$ How are you printing PLA at 175 C? Or did I not look far enough in the gcode? $\endgroup$
    – Zeiss Ikon
    Jul 14, 2021 at 11:46
  • $\begingroup$ At 180 C. Tried first at 200, all ok. This is a new spool. Before that one I printed with PETG at 230 C. No problems. Afcore, every print ends up the same, after 2.5 mm into print head goes inferno :) $\endgroup$
    – HerGiz
    Jul 14, 2021 at 15:18
  • $\begingroup$ Can you try putting a shim over the Z-stop limit switch so the print starts higher, then "dry print" (no filament) to see if this still happens at the same physical height (relative to the machine frame) or after the same number of layers? $\endgroup$
    – Zeiss Ikon
    Jul 14, 2021 at 15:31

2 Answers 2

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Sounds like you have a short in your sensor or sensor circuitry. However, if this is the case the sensed temperature is higher than the actual hotend temperature. Does your hot end go cold when the sensed temperature takes off? A short could also show the hotend temperature going up at an unrealistically fast rate. This doesn't seem to be your case.

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  • $\begingroup$ No. When temperature goes up, so is nozzle shoveling, and after error is detected, I have to wait for the head to cool of to be able to lit Z axes it leaves a big hole around nozzle... $\endgroup$
    – HerGiz
    Jul 14, 2021 at 15:21
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So, the problem is in fact of a hardware nature. By replacing RAMPS 1.4, the problem went away.

Arduino, firmware, G-code... everything is the same, only RAMPS was replaced.

I'm going to find a suitable MOSFET replacement.

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