Random thermal runaway error during print

Anycubic_I3_Mega failure thermal_runaway

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Hi Community,

since a few weeks now, I get random "thermal runaway" errors on my Anycubic i3 Mega. There is no real pattern recognizable. Some prints run without failure, some fail after 1h some after 6h. The graph looks always simular to the attached image. Temperature is slowly dropping as if the hotend does not get any more power. The heat bed is still heating, so i do not thing that it is the power supply. I tried the following so far:

  • Replace complete Hotend including thermostat and heating element
  • Check all "outside" connections
  • Remove enclosure to reduce environment temperature
  • Reduce complexity of print
  • Update FW to latest davidramiro/Marlin-Ai3M

But error persist. So next steps on my list to remove the failure:

  • Add mosfets between mainboard and hotbed / hotend and check all cables in the inside

Any other ideas or had someone similar problems?


MfG mapero

HI guys, so I am having the same error!
I have taken the printer in for repairs, some days it prints great, and others it gives this error.
What is the Mosfet you are talking about?

So some update. After adding mosfets the problem persists, so I removed any piece and checked it. I guess I found the problem. On the Connector Board the ground pin of the extruder was badly soldered. So that it heats up and gets loose. You can also see that the whole solder pad got damage from overheating and is broken. I guess it got some contact, gets hot and looses from overheating.
Since the pad is almost gone, its hard to repair.

Temporally I soldered the cables directly to the board from the other side (pad is okay from this side). No I try to contact anycubic to send replacement. Any experience on this? What is there normal reaction?


Added some images.

I'd suggest that it's the wiring to your heater cartridge as it passes through whatever cabling arrangement you have (cable chains?) as the wires flex during extruder movement while printing.

If you can, install temporary external wiring (or a replacement cartridge) to your hot end and run a print that has failed before.

My hotbed started doing this... when I checked the terminals on the main board the negative was melted and the solder pad half lifted off the board. Swapped in new board with better terminals, old boards used 10A terminals but bed can pull 13A, rated at 15A.

Mosfet also a good idea... if you have a heat gun with a small tip you could also reflow any of the connections involved with powering the hotend.

I had the same effect with soldered joint loosened by overheating.
Mosfet update helps.