Notifications
Clear all

"mmu needs user attention" WITH WHAT?!  

  RSS
WizardStan
(@wizardstan)
Active Member
"mmu needs user attention" WITH WHAT?!

I spent the weekend assembling my mmu.  I've spent all day trying to print one tiny little thing.  As far as I can tell I've had two distinct issues multiple times.

1) sometimes the filament gets stuck in the selector when it's trying to eject it in order to switch colour.  It's still in deep enough that the FINDA detects filament is loaded, so it just keeps trying to unload it, grinding down the filament until it's got no purchase.  I have to remove the spring screws, open the idler, and manually pull out the filament. And I mean I need to really yank on it, hard; it is STUCK.  The end looks fine, it's got the expected "extruder shaped" pointy tip, it's a little bulbous but not any different from any other time I've pulled out the filament manually.  So why is it getting stuck?  My solution is to rip it out, snip a couple inches off the end, and put it back and it's fine, but I can't do this every 20 minutes.

2) the other issue happens almost as frequent and is far more frustrating because I don't even know why it's stopping to complain.  It's not stuck, in fact I can pull the filament out completely without issue and the tip looks exactly as expected (and exactly as it does in problem (1)).  I can't load the filament however because the pulley gear just keeps going backward, trying to unload a filament that isn't loaded.  The FINDA light is on indicating it does not detect a filament, but still, gear drives backward.  Solution is to wait a few minutes for it to timeout and the LCD to display "mmu needs attention" at which point I can open the idler, manually feed the filament through the selector, tripping the FINDA, then closing the idler, start it up again, and it just starts working: eject the filament I just inserted, reload the filament, switch colours if that's what it needs to do (sometimes this happens before the selector moves, sometimes after), then continue printing.  What is it complaining about when this happens?  And it happened SO so much, like every 15 minutes I need to fix one problem or the other.  I started a 5 hour print at 8am and it didn't finish until 7pm.  There is no way that this is normal.

Posted : 27/09/2021 11:29 pm
Diem
 Diem
(@diem)
Noble Member

Make sure the hot-end ptfe tube is correctly inserted.

and

I've not seen this one but it's the sort of thing that can happen if a connection is not properly seated or, (later on) if a wire has work-hardened and the conductor cracked...

Pull and re-insert all connections and if you have a multimeter consider checking continuity.

Cheerio,

Posted : 28/09/2021 12:55 pm
WizardStan
(@wizardstan)
Active Member
Topic starter answered:
More problems

I started the exact same model (just the basic 6 gear bearing made with 3 different colours) and it jammed after 20 minutes.  This time, instead of yanking it out I removed the filament tube and pushed it through, snipping it off that way.  No problems for the next 2 hours at which point it did the second thing again of it trying to unload a filament that wasn't loaded, but I paid closer attention this time and the FINDA light wasn't actually "on", it was kind of flickering.  Popped it up 1/2 mm while it was still doing this (rather than waiting for it to give up and call for help) and it started behaving properly again.

Since that moment, however, every single filament change it treats as a "new spool" or whatever: it ejects the filament, waits for me to "remove" it and "load" the new filament, then press the knob.  I stopped the print, killed the power, and started over again, and it's STILL doing that.

I also had a problem where it would load the filament, cut it, then try to load the next filament and the whole thing would just get jammed up, needing me to unscrew the tube, remove the old filament, in one instance manually move the selector because it had failed to align correctly after the cut.

Long story short, I am having problems.

1) Why is it treating every filament change as a filament unload/load now?  Is there a setting for this that I accidentally tripped?  Or is it possibly related to how I moved the FINDA ever so slightly and now it occasionally thinks the filament has run out?

2) Why did it load a filament, then immediately try to load the next filament?  This is a problem whether the cut works or not (and double problem if the cut didn't work)

Posted : 28/09/2021 4:16 pm
Diem
 Diem
(@diem)
Noble Member

'mmu needs user attention' possibly means the filament has not been detected at the extruder.

FIRST: check all those plugs/connections.

SECOND: unscrew the tube from the MMU and bypass the unit with a filament going direct to the extruder, use a single colour gcode sliced for the vanilla MK3S.

IF you still get spurious filament changes then disable the filament sensor, if it then prints OK it suggests the IR sensor is not triggering so go to page:

https://help.prusa3d.com/en/article/ir-filament-sensor-calibration-mmu2s_2245

If the unload is still failing then go to:

https://help.prusa3d.com/en/guide/how-to-replace-a-ptfe-tube-mk3s-mk3s-mk2-5s-mmu2s_21664

 - 'though don't replace it straight away, check it's inserted correctly and try again...

* * *

Once the underlying machine is running sweetly you can restore the MMU and begin to chase any remaining issues there.

Cheerio,

Posted : 28/09/2021 5:04 pm
WizardStan
(@wizardstan)
Active Member
Topic starter answered:

Didn't touch the plugs.  I checked the sensor status page and tested and verified everything was being detected properly.

Having powered it off and on several times, trying to print, getting these filament reload messages every time, I noticed that the "preheat" option wasn't there.  I noticed it wasn't there earlier but didn't think anything of it since starting a print heated everything successfully and I didn't want to think about yet-another-problem; one big issue at a time, please.  I don't know what possessed me to do so but this time, instead of power-off/on, I just hit the reset buttons.  I hit the reset button on the printer, I hit the reset button on the mmu.

It has now printed 5 layers without asking me to change the filament.  I am... confused as to why a reset would fix things that a physical power cycle would not, but at this point I'm chalking it up to gremlins.

Actually, I noticed there were 5 gummy bears left in the bag from the mmu kit.  Obviously the problem was that setup isn't truly finished until all the bears are gone.  This has been rectified.  Wish me luck.

Posted : 28/09/2021 5:35 pm
WizardStan
(@wizardstan)
Active Member
Topic starter answered:

Nope, I was wrong.  After about 20 minutes it did it again, unloaded the filament and I don't understand what the problem is.

I have the sensors screen up.  It loads a filament, the "Fil. sensor" changes to 1.  PINDA is 1.  It then unloads the filament and "Fil. sensor" changes to 0.  It repeats this several times, loading and unloading the filament, the "Fil. sensor" changing to 1 when it loads and 0 when it unloads.  After a few tries at this it gives up, "MMU load failed".  Why did it fail?  What is it complaining about?  The filament sensor detected filament, the PINDA detects filament.  Where is the failure?  What am I supposed to do here?  It says there's a problem but everything I'm looking at suggests there should not be a problem.

I moved the filament sensor ever so slightly to make it easier to trip but it still wouldn't accept the load, just in and out, 1 and 0, back and forth.  RESET BUTTON(s)!

Now that it's been reset (again) it's running properly (again).  3 successful layers, 9 filament changes, no problem so far.  I think I need more gummy bears.

Posted : 28/09/2021 6:40 pm
WizardStan
(@wizardstan)
Active Member
Topic starter answered:

It was the FINDA.  My original problem was that the metal ball was getting slightly stuck (presumably because I was ripping the filament out and plastic bits were getting stuck to it).  I "fixed" that (without knowing what the real issue was) by moving the FINDA up 0.5 mm.  Moving the FINDA caused more problems in that sometimes it would fail to trip when it should, making the printer think that it was out of filament; I didn't catch this until I sat there, watching it for several minutes, because it barely blinked on before turning off again.  I moved it back, cleaned the dusty metal ball, adjusted the IR sensor position for good measure, removed and reinserted the filament tube to ensure a good fit.

I don't know why I was getting so many jams originally.  Possibly poor fit of the tube, like you suggested.  Regardless, it's happy (for now).

I'm still confused why I sometimes needed to reset everything (as opposed to power cycle) in order to get out of some weird states, but I'm not going to push it.  The important thing is that it's been running for a few hours now without needing any intervention at all.  Problem is fixed, knock on wood-fill.

Posted : 28/09/2021 10:17 pm
Diem
 Diem
(@diem)
Noble Member

OK, but if anything goes awry now - check those connections.  As the extruder and print bed move they stress the wiring.

Cheerio,

Posted : 29/09/2021 12:38 am
JoanTabb
(@joantabb)
Moderator

There is a modified Filament selector on thingiverse which uses a magnet to make the Finda  ball movement more positive on unload. 

Regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 29/09/2021 7:34 pm
Share: