Just prints a blob in the corner  

RE: Just prints a blob in the corner

I am actually having this exact same issues right now. It even jammed the filament in the hot end.

RE: Just prints a blob in the corner

I'm having the same issue.

I've double checked all of the calibrations to no avail.  I3 MK3S+ with MMU2.  I'm wishing I never upgraded to the MMU, as the printer was fine as delivered (assembled).

RE: Important!!

To anyone else who sees this happen, stop the printer immediately.  Whilst mine was doing this the print head was fully lowered.  As the feed motor tried to force more filament down into the hotend the filament, unable to flow out of the nozzle, was forced into the space between the PTFE extrusion tube and the heatsink, leading to me needing to strip the extruder down, unscrew the heatsink, and use force to extract the PTFE tube and 'blobbed' PETG.  A simple enough process, but one better avoided.

Blob in the corner

Buffle,

here is what fixed my issues. I had to reach out to Prusa themselves to get a good answer.

The issue in question is not actually related to the firmware but as odd as it may appear, intended behavior. What's happening here is that the IR sensor doesn't trigger, so the MMU is trying to load filament to the nozzle but simply not reaching it. The following article has more info on how to correctly set it: https://help.prusa3d.com/en/article/ir-filament-sensor-calibration-mmu2s_2245

Re: blob issue

After checking and rechecking the IR sensors, etc., and finding they were still set correctly, I did another full calibration from zero.  Seeing as I had not touched the PINDA Z sensor from factory assembly and it had initially all worked, I had not rechecked this.  After adjusting this and the full recalibration all is working well.  I've learnt not to assume anything and to ensure and double-check that all is set with absolute precision.