I HAVE GIVEN UP !!!!!!!!!!!!!!!  

Active Member

For me, purchasing and TRYING to implement the MMU2 to my Mk3S has been the most unforgettable nightmare.

There is not one continuing sequence of printing that has been consistent - and, mind you, I have only been using Prisa Slicer AND Single filament !!

Below is what I have recently sent to Prusa - but have had no reply - surprising? NO.



Late last year, I sent to you my Prusa i3 Mk3s & MMU because I could not get the MMU to operate as it should.


After receiving the “repaired MMU and my MK3S I can tell you I have spent many, many hours trying to get the MMU to operate – sometimes it printed a thing, immediately after that print I would unload/eject the filament then load to nozzle – enabled print – but NOTHING – just MMU requires attention, or all lights (green and red) started flashing.

I have made zero adjustments to the MMU – except the checking of the PINDA Probe.


I checked the PINDA – is showed 1 when there was filament and 0 with no filament.


I also upgraded firmware for MMU2 and Mk3S.  All up to-date – several times


I also recalibrated using wizard – several times – calibration went up to 1st layer calibration – then same problem – MMU requires attention or all lights flashing – as mentioned above.

Could not calibrate 1st layer !!!!!



As stated previously, this MMU is the most cantankerous piece of technology I have ever had the displeasure to use.

If I am further inclined, I will also post this in Prusa’s forum and elsewhere.


I will now reinstate my printer back to a standard MK3S. – as before when everything worked and the world was good– as expected!!!!!




Please note, IAAM NOT A NOVICE USER !!!




Posted : 13/01/2020 8:49 am
Prominent Member

Why do you load to nozzle? That's not necessary and blocks the selector during homing. No wonder you get errors.

  • Start with an empty printer
  • Turn on the printer
  • Load your filaments (NOT "load to nozzle") (it will do a homing move the first time)
  • Slice your project with "MMU single" profile
  • Start your print
  • Select the filament slot
  • The rest runs automatically
Posted : 13/01/2020 9:13 am
Active Member

Hello lichtjarger.

I have also exactly performed your suggested sequence.

After Load Filament, I set the job to print.

Filament 1 light flashes red/orange

RESULT: MMU requires attention. Press the button (... but which button on MMU ????)

So I pressed middle button - no fix

I press Right button - no fix

I press MMU reset button - 1 out of, say, 10, attwempts - job starts to print.

There is no blockage in filament path

There is no debris in FINDA cavity

There is no obstruction between FINDA and nozzle.

Other times after sending  to start printing - filament loads to nozzle, hotend does 9-point check, then it just sits at front left - and does nothing else.

Finally, why have an option to Load to nozzle when it should not be used to prepare a job for printing ??? Surely this can be confusing to others as well!




Posted : 13/01/2020 11:39 am
Prominent Member

You wrote, that you checked the FINDA. But did you do an IR sensor calibration like described in the handbook (page 15)?

How does the filament behave after selecting the slot?

Usually, after you started a print and selected the slot it will do a homing if necessary and the selector will move to that slot if it isn't already there. Then the filament will be pushed to the extruder. The extruder will pull a bit, then push it back a bit and finally will load it to the hot end.

It might help to know at which step the loading error occurred.

Posted : 13/01/2020 11:54 am
Active Member

Sometimes the filament passes the roller and other times tit does not - even though the filament end has beed straightened and tip cut to an angle

Other times filament passe the roller and just sits there then light flashes - finda previously tested ok.

You see - these as just some examples.

A "normal" user with a fair amount of 3d printing experience - the number of variables affecting the MMU should not exist - as I compare working on the MMU to a novice trying to fix an electronic circuit board.

Documentation covering the majority of variable error situations could help - but not in existence.

Posted : 13/01/2020 12:33 pm
Noble Member

Hi Andreas,

This is a forum from users to users. If you're looking to expedite your refund request, then it's the wrong place.
If you still want to make it work then you should start to check your filament path and the sensors. The root cause for MMU2 issues for one filament prints are 99% hardware related.

This post was modified 6 months ago by nikolai.r
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Posted : 13/01/2020 6:21 pm
Prominent Member

Posted : 14/01/2020 6:57 am
Active Member

I must declare that Prusa support has communicated with me regarding my issues - and I must say that I am most humbly surprised by their contact, their professionalism, and what they have proposed.

In fact - they have offered to refund me, in full, the cost of the MMU or to translate the cost value as a voucher towards my future purchases I effect with Prusa.

I declare I did not expect this and I bow to Prusa's ethical customer-oriented standads.

Nevertheless, as an aged and disabled pensioner I do prefer that life is stable and without stress - so it is still my intention to revert my printer to Mk3s (no MMU). It is sad, however that my grandchildren cannot receive multi-coloured toys - as I had dreamt and hoped.

To all who have responded to my post - MY SINCEREST - THANK YOU.

Posted : 15/01/2020 12:51 pm
Estimable Member

Hello Andreas,

Thank you for your post and sharing your insight. I have been reading this thread carefully and I can relate to your frustration, because I have seen similar reports. Prusa's customer service is very forthcoming and I have had similar experiences with them, so hats off!

I also want to go multi-color because today I do everything manually which can be a bit of a challenge. I thought about the MMU2S, but I am also toying with the idea of purchasing a Mosaic Palette Pro. I am not sure what the better choice is, but what I like about the Palette is the fact that all the heavy lifting takes place in a separate unit, not the printer itself. I think the handling will be a lot easier and less prone to errors.

I'll let you know how this goes, perhaps it's something to consider for you as well. Both systems have drawbacks of course, but we all know the MMU's weaknesses...

3D Druck für Einsteiger leicht gemacht: www.3d-druck-lernen.de...
Posted : 15/01/2020 1:35 pm
New Member


you are not alone. I have found the MMU2 an incredibly frustrating experience. And, although Prusa support are incredibly helpful, every engagement seems to turn into a protracted re-check of things that I have previously checked, all over chat and late at night. I too am very disappointed with the product, and after many late nights (early mornings) of really wanting to get it to work, am probably going to throw the towel in. I can't go any longer having my printer out of action. My MK3S was running brilliantly before I took on the MMU2 but it now seems to constantly want to be recalibrated. MMU2 constantly "needs attention", and I've not yet had a successful print from it. So much of your experience mirrors mine.

Posted : 03/04/2020 5:56 pm
Active Member

Derek, I share your pain.

As you rightly stated - Prusa support do their utmost to assist.

I am now back to using my MK3S as a standalone. I am now happy!

Posted : 04/04/2020 6:52 am

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