MMU2S Hot End shuts off
My MMU has started demonstrating some very irritating behavior. At random points during a multi-material print, the hot end will shut off during a material change. By the time the new filament reaches the nozzle, the hot end has cooled enough that the cold extrusion prevention kicks in. At that point, the filament retracts, and the printer resumes executing the gcode, but just printing in air with no filament. I have seen this most often when the MMU has to attempt a filament load more than once - it seems like the multiple attempts cause it to shut off the hot end as if it were pausing, but it doesn't actually pause. I can tell the filament is actually triggering the IR sensor by watching the display (I have it set to show the sensor status), but the printer still fails to turn the hot end back on. So far, of the last 9 prints I have tried, none have gotten more than 75% of the way through before the hot end malfunction kicks in.
RE: MMU2S Hot End shuts off
I have had this happen to me too multiple times now. I will add that I am running octoprint to control my printer so I am wondering if there might be something going on there too.
RE: MMU2S Hot End shuts off
I'm wondering about OctoPrint as well (I also use it), but I have, until recently, been able to print multi-material using it. I tried printing from the SD card yesterday, but had to cancel it when the filament change failed. I may try again on the weekend and I can watch it run.
RE: MMU2S Hot End shuts off
Not sure if you are running the newest firmware, but I did find this in their most recent 3.12.2 firmware release: https://github.com/prusa3d/Prusa-Firmware/releases/tag/v3.12.2. There is a section about octoprint doing some M112 Emergency G-Code. Wonder if it is related and which version of octoprint fixes this.
RE: MMU2S Hot End shuts off
Sounds to me like maybe the length of the filament path from the MMU2S to the nozzle has changed. There is an advanced menu in the MMU2S to adjust it. There’s a how-to somewhere in the online support pages at Prusa. Good luck!