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MMU2S freezes mid print?  

Active Member
MMU2S freezes mid print?

Hi all, I have a very strange (but troubling) problem with my MK3S & MMU2S.

This past week I updated both the MK3S and MMU2s to the most recent firmware. I have to print rather large parts that consume approximately 1.2kg of filament, thus I require spooljoin. The problem I am encountering is:

- The printer doesn't pause when the filament runs out past the FINDA sensor (thus the filament goes all the way down to the extruder)

- If I pause the printer to manually pull out and change the filament it will freeze saying to fix the MMU2S problem and press the button to resume.  The problem here is that the MMU2S has a green light and doesn't detect a problem, so pressing the button doesn't do anything and it remains frozen.

The only workaround I found was to press the reset button on the MMU2S, at which point it continues on with all 5 LEDs flashing orange. What is happening here? It seems like a firmware bug - I've been using this printer with zero problems up until this firmware update.

Posted : 25/01/2021 10:29 pm
RE: MMU2S freezes mid print?

check that your ball bearing is free to muve under the Finda, on the MMU2S Selector

or you could consider printing a modified selector block, with a magnet below the ball, to ensure that it moves down when the filament end passes

I think this is available on thingiverse


regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 25/01/2021 11:56 pm
Active Member
Topic starter answered:
RE: MMU2S freezes mid print?

Hi Joan,

I verified the FINDA unit functions properly. It has been running for a year with no problems actually.. What is perplexing is that the actual MMU2S and MK3S lock up in terms of communications. The units become unresponsive to any inputs.. even prusa support told me "unplug the machine and pray" (AKA use the blackout recovery function). So the problem seems to be firmware related?

For example, the LCD says to fix the problem then press the button on the MMU2S. Well.. the MMU2S has the solid green LED, indicating there is no problem.. thus when I press the buttons, it doesn't send a response to the MK3S because the firmware is not in a state to send anything. Essentially it seems that the two units fall out of sync and it can only be resolved with a system reset. I actually noticed that it will do this when I pause the printer or select "change filament" on the LCD.

This post was modified 9 months ago by Steven
Posted : 26/01/2021 2:40 am