BUG MMU2S filament load failure with firmware 3.13.x and 3.14.0 (MMU2S fw 3.0.2)

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rcurcu

(@rcurcu)

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BUG MMU2S filament load failure with firmware 3.13.x and 3.14.0 (MMU2S fw 3.0.2)

**Printer type** - MK3S+

**Printer firmware version** - 3.13.x and 3.14.0

**MMU upgrade** - MMU2S

**MMU upgrade firmware version** - 3.0.2

**SD card or USB/Octoprint**

Not applicable

**Describe the bug**

Filament load fails on MMU2S with new firmwares 3.13.x and 3.14.0 No issue with previous firmware 3.12.2

**To Reproduce** Firmware 3.13.x or 3.14.0

Load filament in slot 1 of the MMU2S. Via the printer menu, load the extruder with filament 1. Most of the time the filament do not load properly.
If it succeed in loading, the filament cannot be unloaded at all.
See also explanation with photos below.

**Expected behavior**

Filament correctly loaded in the extruder and successfully unload from the extruder.

**G-code**

Not applicable

**Video**

Not applicable

**Photos / Explanation **

I put a small paper ruler on the Idler and an arrow on the fixed part of the MMU2S to measure the move of the idler.

When loading the filament with the firmware versions 3.13.x or 3.14.0 on the printer and the matching version 3.0.2 on the MMU2S I see that the idler is taking this position during the load of the filament in the extruder :

The load fails and the filament nearly never reach the extruder…

And the same position when unloading :

The filament remains blocked in the ptfe tube between the extruder and the MMU2S (« bowden tube »).

When loading the filament with the firmware versions 3.12.3 on the printer and the matching version 1.0.6 on the MMU2S I see that the idler is taking this position during the load of the filament in the extruder : We see clearly that the idler is moving few millimeters further (3-4).

Once the filament reach the extruder gear, when see that the idler is reversing to this position.

The filament is successfully loaded and extruded.

When unloading, again, the idler is moving a little bit further… and the filament return without any issue in the MMU2S where it’s ‘parked’ for next use :

It looks like we new firmwares (3.13.x / 3.14.0) the idler is positionning the ballbearing (the blue circle) of the idler this way and so do not push at the top of the extruder gear;
This is also an explanation why we see flat marks on the filament (filament is mangled) where the gear is « slipping » on the filament :

With firmware 3.12.2 (and probably older), the idler is positioning the ballbearing of the idler this way and so push at the top of the extruder gear :