MMU2S Loading problem  

New Member

Hi there,

I just finished the assembly of my MMU2S unit and now I am completely stuck with the chapter 7.3 "First Layer Calibration" in the "MMU2 Printing Handbook".
The issue it, that there is no filament leaving the MMU unit beyond the FINDA-sensor.

Steps I perform:

  • I let all 5 filaments load with LCD-menu -> load filament -> load all.
  • the selector takes the filament and loads according written in chapter 6.1 before moving to the next filament. The loading procedure ends successfully (at least according the LCD).
  • I can see the end of the filament when I look into the small PTFE tubes.
  • However, when I start the First-Layer Calibration from the LCD (e.g. for Filament 4) no filament is sent beyond the FINDA-sensor.
  • The following happens:
  1. I perform "Load all"
  2. I start "First Layer Calibration", then the bed and the nozzle is heated up
  3. this is then followed by controlling the z-height at the well-known 9 positions on the bed
  4. Then the MMU-selector moves to first filemant (since I have chosen filamtent 1)
  5. MMU does something and the LED for filament 1 switches between green and red, but no filament is visible in the PTFE beyond the FINDA
  6. LCD says "MMU load failed", but filement LED on the MMU is green!
  7. Sensor info says 0 for all three sensors.
  8. I need to reset the printer with the X-button near the LCD as I cannot cancel the first-layer-calibration procedure otherwise.
  • I checked the FINDA-sensor for proper operation pushing some filement from the rear side and noticed the Support/Sensor-Info/FINDA-value going from 0 to 1. So this seems to be ok.

Main Firmware: 3.8.1-2869
MMU Firmware: 1.0.6-372.

Any help appreciated, as I am completely stuck and cannot even print with one color.

One strange thing I noticed:

I spent many hours today and I noticed twice a strange behaviour: When I told him to load filament 1 actually the filament 5 was loaded into the air (since the selector was at filament 1 and the shart PFTE-tube for filemament 5 was open). But this happend only twice...


Best regards


Posted : 09/02/2020 7:48 pm
New Member

Hey Leo,

Just been playing with this myself. 

First, you said there was a zero reading on all 3 sensors... Part 7.1 of the book shows how to calibrate this and it's really important as it doesn't work otherwise but I don't think it's needed for the feed from the unit to the extruder.

I managed to get the first four filament loaded to the extruder by going to the "Load to Nozzle" item in the LCD menu... apart from that I'm still trying to get it working on the 5th filament loader.

Posted : 08/03/2020 5:54 am
New Member

Hi all,

I'm also experiencing the same issue after performing the upgrade from MK3 MMU2 to MK3S MMU2S this weekend. The printer was performing fine before.  At first, I had the IR calibration issue, the first layer calibration would end up in a blob being generated, but at least the filament was leaving the MMU2S. For some reason, it now refuses to load filament up to the extruder.

@Leo, I second matt, please check your calibration. And just in case, ensure you've used the proper IR cable, the kit includes one MK2.5S and one MK3S cable (You'd want the black-red-white wire one for the MK3S).

Cheers guys,



Posted : 30/03/2020 2:20 pm

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