Unload problem - Filament extruder blocks filament while pulling back.
Hello, I always have the same annoying problem with the MMU2 that makes me nuts:
I have a Mk 2,5s with the MMU2s, with recent firmware for printer and MMU. The problem is the frequent problems during unloading the filament.I have tried to adjust most MMU2 relevant settings in the Prusa slicer, (I also tried to adjust the ramming settings.) and I adjust the length of the filament through the secret menus on the filament frequently for new filaments. My filament tips seem to be fine, no stringing.(the only strange thing is that they are not symmetric)The sensors are well calibrated.
During Unload happens the following:
The filament cannot unload and the tip is still below the extruder (Bondtech gears)
The filament is then still held back by bondtech gears, which are blocked. It is not possible to pull it out manually (when unscrewing the Festo couplers and the Bowden tube).But as soon as the mmu is "parked" and gives the message "MMU needs user attention" or something like that, then the motors of the extruder release and the filament can be pulled back with hardly any resistance. So it seems the filament is held back by the extruder motor which is blocked.
Meanwhile the MMU2 tries to pull back the filament but just grinds a hole into the filament.
This happens on all lanes and it does not follow a pattern. Sometimes I can print 5mm high without a problem, but the problem is persistent also over a lot of firmware and slicer updates.
Any ideas how to prevent the extruder from blocking the process of pulling out the filament or why the filament in certain cases is still stuck under the extruder and blocked by the extruder?
P.S.: i also overtightened the Extruder screw which one user recommended, it did not help.