MMU randomly will not load filament several hours into print, no clear info why.
 

MMU randomly will not load filament several hours into print, no clear info why.  

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patrick.l14
(@patrick-l14)
Active Member

I'm getting really frustrated with all the MMU2S failures that are happening for seemingly no reason! I found the printer this morning paused halfway through what was mean to be a 10 hour print (23 color changes total), just sitting there, it offered the option to resume, but when I tell it to resume it loads the filament, forwarding it into the extruder (I verified the IR sensor is detecting it), but then it immediately retracts it back into the MMU for no apparent reason. It tries the same thing once more, then goes back into the paused state it started in. Why is it doing this, and providing no explanation as to what's going on? I tested the same procedure several times, always exactly the same behavior. What is wrong with it? And  why is there no feedback at all onscreen (or to octoprint, which was monitoring (but not controlling)) this print? Why is it that even when there is feedback it's the unhelpful "MMU load failed", leaving us to try to decipher the debug LEDs for what little extra information they give? 

I eventually tried to manually "load filament to nozzle from the menu", which seemed to not communicate with the MMU at all, as it just asked me to confirm when filament was extruding, while the gears were turning with no filament to use. After pressing the MMU's buttons, trying to get something to start working, the printer got into an even more confused state, in which the screen was black except for the selection cursor, which could be moved between 2 empty options on the last 2 rows of the screen. Clicking on either of them did nothing, leaving me no further choices but to restart the printer, and give up any hope of completing the half-finished print.

 

Honestly, I'm rather perplexed as to why the 1st party add-on device meant to upgrade my Prusa i3 Mk3 (which, by the way generally behaved flawlessly without the MMU), seems so bad at communicating with the main printer, and fails so often, even when there's visibly nothing wrong? It feels as if it was some 3rd party device from China tacked on as an afterthought, not the official upgrade from Prusa themselves. I welcome any suggestions as to what went wrong in my print, or any potential good news on upcoming firmware updates that provide more helpful feedback or improved error recovery.

thanks,

Patrick

Posted : 23/07/2019 9:44 pm
Nikolai
(@nikolai-3)
Noble Member

Fail info is usually coming from the MMU. fast red blink = unload issue, slow red blink = load issue.

The reason why need to be investigated. Assuming you have everything perfectly assembled and had working before with MK3s, most common errors are:

  1. IR sensor not perfectly calibrated
  2. IR sensor not perfectly calibrated
  3. IR sensor not perfectly calibrated
  4. Screw tension on MMU and Extruder is not perfectly calibrated
  5. Too hot filament temperature/bad filament causing  bad filament tip

Hope that helps for the first investigation.

 

Often linked posts:
Going small with MMU2
Real Multi Material
My prints on Instagram...
Posted : 23/07/2019 10:05 pm
canady.dave
(@canady-dave)
New Member

I have the exact same problem.  It will print successfully, switching filaments back and forth through the print.  After about 12-15 filament changes, it just will not load any more.  It gives an MMU error, slow flashing red light on the MMU.  I went through the procedure as documented to fix the problem, and it feeds the filament all the way through to the extruder assembly, then back to the MMU, then back again to the extruder, then back to the MMU (two cycles).  Then the MMU red light flashes slowly.  Repeat.  Repeat. Repeat.  No luck after many repeats.

 

I would like to know why it goes successfully for a while, then errors out and cannot be fixed.  If I shut everything off and reprint, it prints fine for a while, then just stops again.  I'm only using the test sheep gcode.  I have checked all the settings above, but nothing fixes the problem. I have tested with other Prusa-provided gcodes for MMU2S and have never made it to the end of a multi-color print.  If I use just one color for an entire print, it loads and works perfectly.

 

Please help!

Dave

 

This is very disappointing. 

Posted : 23/07/2019 11:55 pm
Nikolai
(@nikolai-3)
Noble Member

@canady-dave: Print again and once you have this error, pull out the filament, make a picture of the filament tip and post it here.

Often linked posts:
Going small with MMU2
Real Multi Material
My prints on Instagram...
Posted : 23/07/2019 11:58 pm
canady.dave
(@canady-dave)
New Member

Here is a picture of the filament.

Posted : 24/07/2019 1:50 am
brian.l32
(@brian-l32)
New Member

i ran into the same problem with the blank display with only 2 empty options, neither of which would do anything.  I pulled the cord out of the wall and plugged it back in and took advantage of the Power Panic feature to save the print.  Very happy to be able to save my print!

Posted : 08/10/2019 9:53 pm
Pixel
(@pixel)
Trusted Member

the filament seems to have a bit of stringing but not a big issue really, this is exactly what the blade in the selector is for as it will cut off the stingy part when it comes along.

Posted : 18/10/2019 8:15 am
michael.t66
(@michael-t66)
Trusted Member

@canady-dave

Ok, two things that might help:

Check your IR sensor for the filament. That is the ONLY reasons it would pull back the filament. I advice to solder an LED onto the IR sensor. You will be astonished how bad it works (due to our setup) although it seems to be fine by looking at the display. If you experience flicker, there is your reason. It needs to be solid (also check during print although not critical for loading, but it gives you an idea)

PLA tends to enjoy heat creep. It might be hard to detect as it depends on what is being printed, but it is there. Believe me. So, get rid of it (usually unloading issues). Check my older posts for a solution or take any other.  

My MMU(s, rather one at the moment, as the other one goes live tonight for the first time) showed the same thing and I believed everything was ok. Lots of fixes later it IS ok and it is WORKING. Record so far: 2000 filament changes on a print over 4 days and two loading errors. 

This post was modified 1 year ago by michael.t66
Posted : 19/10/2019 6:48 pm
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