Clear all

Odd (and breaking) print startup behavior  

New Member
Odd (and breaking) print startup behavior

MK3S w/ MMU2S 

I've verified I'm running the latest firmware

On print start or independent load operation, extruder positions nozzle 1mm from print surface for test push of filament. It used to do this operation from a few cm away at least. Print first layer calibration is fine (when the printer doesn't break itself).

In the past, the first push bubbled up around the nozzle and dragged into the print unless it was lucky to break off during the test layer at the front of the print bed. Lately, filament has about a 70% chance of not making it out of the nozzle. I've disassembled the extruder and there doesn't appear to be any damage to the ptfe tube. no clogs either.

This seems to just be a behavioral issue with the firmware. I don't think it's a gcode issue for individual prints. 

I'm at my wits end. support chat has been no help at all after days on with them. they just recommend hw & calibration changes I have already checked and double checked many times. They won't acknowledge or address the idea that it might be firmware. 

does anyone have any similar issues? Ideas for what to debug next? It seems like prusa is in a decline, none of the documents are up to date and the website is a mess..... might jump ship to a brand with active support and userbase

Posted : 19/06/2022 9:27 pm
New Member
Topic starter answered:


Changing the nozzle seems to have fixed the clogging issue, but the odd behaviors remain. I'll elaborate on them below:

  1. Printer "home position" where filament is test pushed before every print is within a mm from the print bed
    1. apparently it's possible to adjust this manually in the gcode of each print? but I'm hoping for a configuration change solution... other people seem to have had this issue in 2019, but I haven't seen it until 2021
  2. Printer will load filament to a cold nozzle (now confirmed as unclogged) and try to push it
    1. causes extruder gear and mmu2 gear slip, eating into filament and creating filament dust in extruder

I'm hoping there's someone out there who has a homebrew solution to this, because my 48+hours on with Prusa support has led nowhere. They won't even acknowledge that it could be a firmware issue. It's also been a few months since I started troubleshooting this issue and contacting them and none of the firmware updates since then have fixed it..

Posted : 25/06/2022 3:55 pm