Thermal Runaway post shut down melted heat block

Basic Information:

Printer Model: Tronxy XY 2 Pro
MCU / Printerboard: MKS Gen L V 1.0
Host / SBC Host (aarch64, 64bit) Version: v0.12.0-179-g434770ea OS: Debian GNU/Linux 11 (bullseye) Distro: MainsailOS 1.3.2 (bullseye)
klippy.log: (1.8 MB)

Describe your issue:

So I’ve been learning klipper this last week. I’ve fought through many of my own fuck ups and all kinds of issues. I was making it a point t o dig and figure shit out myself because I’d learn more that way. I think this one I should reach out for some help with…

Print was running fine walked away from the printer for maybe 25-30m Klipper was in MCU shut down. My heat block had a gentle glow forming and there was still 24V coming from my board non stop to the heater… I clipped the wires so I could leave the fan running to minimize any more melting.


I checked the thermal runaway stuff before and if it acted funny at any time klipper shut it down. Why on earth is my heater still getting power. What did I fuck up.

I would recommend uploading all your configs as well.

You might want to ask on the discord.

I don’t see anything wrong in your config.

Klipper shutdown because your hotend exceeded it’s temperature.

In all honestly it sounds like your hotend MOSFET on your board is shot. They often fail closed and provide constant power.

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Sounds like it’s time for a new board. Too bad it didn’t wait just a little longer I was shopping for one already.

Ok I think I found it. So the fan is running on HE1. I moved the extruder to the HBED pin and when the light for HEO comes on the fan runs so when the fan was running after shut down it was throwing the heater voltage.

Unless you’re using some industrial sized fan, you don’t need to use the heated bed/extruder power outputs, you should have dedicated fan pins for this.

Small DC fans (like used in a 3d printer) only require usually usually less than .25 Amps. The heater/extruder outputs are made for 3-5 amps or more.

Way overkill and runs the risk of turning on the wrong one like you’re describing which could easily burn your house down if you didn’t walk back in to check it.

I wholeheartedly agree with you. It’s a lack of pin outs on the little msk gen l v1.0 I had from a parts printer. I figured it was better to have control over it and I wouldn’t do any harm running it on a different port. lmao how wrong was I!

I have a new board on the way hopefully it’ll be here Monday then I don’t have to worry I’ll have all the ports I need.

Yeah I figured with the melted aluminum I was in the house burning down territory. That’s why I didn’t hesitate to order a board that I don’t have to fiddle aorund with like this

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When you get the new board, I recommend your first step is to go through the steps at Configuration checks - Klipper documentation . The steps there are intended to exercise the heaters and shutdown sequence in a controlled setup to catch pin assignment errors.