What happened?
While loading to the extruder, as soon as the filament sensor detects a filament the printer performs an automatic loading check. If the check fails, this error is shown. Each failed load might be accompanied by the printer beeping.
The printer’s automatic loading check loads approximately 40mm of filament and then unloads 30mm of it. If the filament sensor stops detecting a filament at any time during the process, the error is shown. This process is very sensitive, so making a precise Filament sensor calibration is needed in order to prevent print defects.
While your MK3S+ is performing the loading check, solid blocks should be generated on the bottom of the LCD representing the IR filament sensor detecting a filament during the process.
If there is a line instead of any blocks (drop in the sensor’s reading), this means that the sensor stopped detecting filament at that moment, resulting in a failed loading check. The printer then retries the load. If the cut function is enabled, the MMU tries to cut a filament tip. If the drop while loading persists even during the retries, the printer unloads the filament and shows the error.
How to fix it?
- Redo the IR filament sensor calibration (MMU3, MMU2S).
- While the printer is Idle, you can use the Loading test in LCD menu -> Settings -> Loading Test to verify the filament is able to load properly.
- Undo the PTFE tube from the FESTO fitting and pull the filament out by hand to inspect it. The last 40cm (15") of each should have no dents in it, or the gears won't be able to grab the filament. Cut off part of the filament with defects such as indentation or a deformed tip. Make sure the filament end is straight and has a sharp tip at the end. Reattach the PTFE tube and hit Retry.
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- Inspect the extruder to rule out a hardware fault such as misaligned Bondtech gears or Extruder Idler shaft not inserted correctly.
- In case the issue continues to happen over multiple unloads, check the extruder for clogging.
- Inspect the filament spool and the buffer for excessive friction or filament jam. Make sure the filament is able to move freely.
- Use only high-quality filaments. Certain poor-quality filaments or very specific types of material might not work correctly with the MMU.
7 comments
I tried sending a message to prusa but hilariously enough the button you press to submit doesn't work.
Good luck everyone!
None of of the above things fixed it for me. What did work was adjusting yhe axel on the idler door. https://forum.prusa3d.com/forum/postid/608180/
Hi! Thanks for sharing. A similar case has been reported before. A note about this has been added to the article.
I've got the feeling, that Prusa stopped quality control for the old printers and delivers just a mess with the new firmwares. My printer runned without issues, until I've updated to the newest firmware and installed MMU3. Now I've got such issues with the MMU.
Sorry, but I'm really frustrated, how bad also the new MMU3 works compared to the AMS, this feels like making fire with sticks and stones in the rain, while looking to the sky and seeing Bamboo building a space station.
Why riding on a dead horse and even try to improve it? Porsche did it great with the car layout and the engine in the back, but maybe Prusa needs to accept, that they are not Porsche.
I have so little issues with the mk4s and mmu3 that I am definitely purchasing another set come christmas to double my production rates.
One thing nobody ever seems to talk or think about is how much waste babmu creates.
I have a 5 color bulbasaur model that is basically 2.5" by 2.5" by 3". With the mmu3 the model takes 55 grams of filament with 110 grams of waste to the purge. The waste number can be as low as 85 grams if I purge to infill. This is for a single model by itself. Either way, waste is basically double the model weight.
The bed can fit 9 models and if I print 9 models the waste stays the same. So my print to waste ratio goes from almost 1:2 to 4.5:1.
With bambu the waste amount almost triples thanks to their stupid purging system. I tried this on my friends AMS with only 4 colors. I was gobsmacked that the waste created was nearly 300 grams for 495 grams of models!
If I print 100kg in a year just printing bulbasaurs, the total waste amount would be 22kg on my mmu3. That is $400.
If I do the same on a bambu I waste nearly 66kg or $1200.
Bambu sucks and their whole AMS system was designed to be as wasteful as possible.
In one year I will have saved enough in filament waste costs compared to bambu to buy another mk4s and mmu3.
"But bambu is so cheap you could buy 2 or 3 printers for that price!" Lol sure. If you don't count the worst thing about bambu being the high cost of filament waste, then sure. But if you believe in mathematics then there is no other viable choice.