Why is the MMU trying to retract the filament during the loading phase
 
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Why is the MMU trying to retract the filament during the loading phase  

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MileHigh3Der
(@milehigh3der)
Honorable Member
Why is the MMU trying to retract the filament during the loading phase

Why would the MK3S/MMU2s try to load the filament, and then try to unload it all the way back to the MMU, to try to load the filament again???

What makes this fatal is that for some reason, the MMU can't retract the filament?  It seems the filament is far enough into the extruder that the MMU can't pull it back- and for some reason the Mk3s isn't trying to drive it back either.

It seems the MMU doesn't have enough strength and purchase on the filament to withdraw it???

The lack of full documentation on the filament handling is crazy.  The lack of error codes is something I've never  seen before.  Fail, ok, things happen.  Tell me what is wrong, and all I get from the printer is "I'm fine", "whatever', and "what do you want for dinner?".

Posted : 07/12/2020 8:38 am
karl-herbert
(@karl-herbert)
Illustrious Member
RE: Why is the MMU trying to retract the filament during the loading phase
Posted by: @milehigh3der

Why would the MK3S/MMU2s try to load the filament, and then try to unload it all the way back to the MMU, to try to load the filament again???

What makes this fatal is that for some reason, the MMU can't retract the filament?  It seems the filament is far enough into the extruder that the MMU can't pull it back- and for some reason the Mk3s isn't trying to drive it back either.

It seems the MMU doesn't have enough strength and purchase on the filament to withdraw it???

The lack of full documentation on the filament handling is crazy.  The lack of error codes is something I've never  seen before.  Fail, ok, things happen.  Tell me what is wrong, and all I get from the printer is "I'm fine", "whatever', and "what do you want for dinner?".

In most cases, incorrectly adjusted sensors are responsible for the strange behavior of the printer and MMU2.
I would check the switching status on the LCD (Support -> Sensor-Info) for both sensors. If the filament is loaded, the status 1 should be displayed, unloaded = 0.

https://help.prusa3d.com/en/article/lcd-menu-i3-pre-firmware-3-9-0_1876

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen.

Posted : 07/12/2020 12:28 pm
Robin
(@robin)
Noble Member
RE: Why is the MMU trying to retract the filament during the loading phase

Hi milehigh3der,

Karl-herbert is right, strange loading behavior is normally caused by inappropriate sensor info from filament sensor or FINDA. It is sometimes hard to diagnose due to the lack of a proper error log or indication. The LED-mods generally suggested in most threads do help find the problem if you happen to be present to watch the problem occur.

You are right as well, the documentation sucks. 🙂

Your specific problem sounds like the filament sensor on the extruder does not report the filament loaded even though it is already engaged with the bondtec gears. As Karl-herbert said: recalibrate the filament sensor and try again...

If at first you don't succeed, skydiving is not for you.
Find out why this is pinned in the general section!

Posted : 21/12/2020 10:09 am
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