MMU needs user attention at end of print?  

RE: MMU needs user attention at end of print?

I see the same thing. IMHO the tip is larger then in multi color prints (color changes). I wonder what the last move is. Does it do any cooling moves like inbetween color changes ?

RE: MMU needs user attention at end of print?

Hi Sebastian,

as I wrote I currently I only use one color, so no color changes. It is the first and only unload that fails.

I just don't have a clue why it might complain. I can pull out the filament easily, both filament sensors work fine but still I get those five blinking LEDs (or ten). The UI of the MMU2 is really horrible - unlabeled buttons with varying functions, cryptic blink codes and poor documentation on top.

RE: MMU needs user attention at end of print?

All the LED's blinking refers to a driver error- meaning that there was "insufficient power for the driver". There are quite a few posts about driver error stashed around on here somewhere.

RE: MMU needs user attention at end of print?

I read you fixed this by lowering the stepper current in the firmware...

I have to say I am not willing to go too deep into debugging the MMU2 - like trying to build my own firmware, hooking up the scope to the power supply. This is really Prusa's job!

RE: MMU needs user attention at end of print?

Most common issue during unload is a long filament tip. What sometimes happens is following:

MK3 is retracting the filament until the IR sensor is triggered. Then MMU is getting a signal to unload. If during this unload the IR sensor will be triggered (for whatever reason), the MMU is going into error state (all leds blinking). 

I’ve compiled a new MK3s firmware which gives MMU a little bit more time to retract. Since then I had not this kind of issue. 

Please try to reproduce this issue and closely watch what’s happening and if you can see the behavior I’ve described. If yes, then there are multiple solutions how to solve it.

RE: MMU needs user attention at end of print?

@nikolai-r

I'll watch it - although - most prints run overnight and I just see it failed in the morning...

I have the impression it happens more with some (crap?) bq filament, being more stringy - maybe needs lower temperature?

Would you share your compiled firmware?

RE: MMU needs user attention at end of print?

Sure thing: https://forum.prusa3d.com/forum/original-prusa-i3-mmu2s-mmu2-general-discussion-announcements-and-releases/mmu2-real-multi-material/paged/4/#post-171410

RE: MMU needs user attention at end of print?

I've been having this exact same problem, especially with one specific color.  I'm also doing a single color print.  After a lot of frustration and then finding this post, I finally found a troubleshooting document which helped.  You have to push the correct buttons in the correct order. 

When I just powered off and back on, things seemed to get worse even after I'd pulled out all the colors and poked a piece of PLA through every hole to be sure it was clear.

https://help.prusa3d.com/article/bysrimn4jc-mmu-needs-user-attention

For me, the answer was

1. push down the blue ring where the extruder tubing connects to the MMU and gently pull the tube off
2. push a few centimeters of filament back toward the extruder in the 'loading' direction using your fingers so you have access to the filament tip
3. cut the tip at a clean angle (with the tubing off, you'll have access to cut it)
4. push the middle button on the MMU (it will retract the filament backward and forward)
5. if the LEDs change to alternating red/green, you fixed it (otherwise try again or try something else from the link above)
6. once fixed, push the tubing back on then push the right button on the MMU
7. it will heat up the extruder again (it doesn't know the difference between the middle of a print and the end of a print)
8. after the extruder is hot, it will step to the final screen showing the print time

Hope this helps someone else running into the unload problem at the end of a print

Bill

RE: MMU needs user attention at end of print?

In the "maybe this will help" category:  My problem with the MMU errors were tied to one of two problems:

1. The set screws on the filament selector were loose.  Easy fix.  Tightened them and they've not come loose since (many prints later).
2. The filament was soft and the selector components just squished the filament and it wouldn't move.  This is especially a problem with the water soluable PVA.  A terrific fix for this was to bake the whole roll of filament in my home oven at 170 degrees F for a few hours.  When the filament comes out of the oven it is super soft, but after cooling, it is rigid and better behaved.