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MMU2s Suddenly selecting wrong filament  

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jhitesma
(@jhitesma)
New Member
MMU2s Suddenly selecting wrong filament

The past two weeks I've been printing a series of 2 color panels for a modular synthesizer I'm building.  This has been working fairly well up until Friday.  I haven't changed my workflow or any settings in Prusa slicer or on the printer - but suddenly when I'm running prints the printer is selecting the wrong filament.

I'm using Filaments #2 and #3 which are white and black PLA respectively.  I have #4 and #5 loaded with PETG which I'm not using on this current project.  

In Prusaslicer it correctly shows extruder #2 and #3 being used:

 

But when I run the print instead of changing to #3 it changes to #4 (and the printer display says it's loading #4 so it's not that it thinks it's loading #3 and getting #4 by mistake somehow.)

I've looked at the gcode but am not familiar with the codes used for filament change and couldn't find specs on them to figure out if this is a slicer issue or a printer issue.  

Any ideas what could be causing this?

 

 

 

 

Posted : 14/09/2020 4:14 pm
john.w80
(@john-w80)
Eminent Member
RE: MMU2s Suddenly selecting wrong filament

I have had several issues with strange MMU2 behavior that were all fixed by disconnecting and reconnecting MMU2 control cables at the main board. You might give this a try.

Posted : 14/09/2020 4:20 pm
jhitesma
(@jhitesma)
New Member
Topic starter answered:
RE: MMU2s Suddenly selecting wrong filament

I'll give the old disconnect/reconnect a try.

For reference I uploaded the current g-code that's giving me issues here:

https://gist.github.com/jhitesma/45f05512be6c8f2d6a126eda6c8cd4bb

 

It looks like T1/2/3/4 are the commands that should change filament...but even though this print only uses extruders 2 and 3 I only see T1 and T2 commands in the gcode so there seems to be something I'm really not understanding about MMU gcode.

Posted : 14/09/2020 5:13 pm
jhitesma
(@jhitesma)
New Member
Topic starter answered:
RE: MMU2s Suddenly selecting wrong filament

Figured it out!  Just watched another attempt more carefully.

After it finished with extruder 2 and goes to do the first filament change it does load filament 3.  Then makes 2 passes across the wipe tower - but nothing appears to come out.  Then it unloads filament 3 and displays a message saying loading filament #4 and starts to load #4.

Which had me scratching my head why it would do that...until I remembered I have spool join on.

Apparently my #3 filament (black, hatchbox - even though my profile says Prusament I've found I get really good results with hatchbox on the prusament presets.) which is nearing the end of the roll has gone a bit brittle and snapped inside the PTFE between the buffer and the MMU.  It wasn't visible because every time I looked the ends were pressed against each other and where it was positioned in the tube. 

I only found it because I decided to try reloading #3 and when I did I finally noticed the break.

 

 

 

Posted : 14/09/2020 5:43 pm
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