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MMU2S idler problems  

MMU2S idler problems

Finally, since I got the mmu2s kit I’ve not known how the unit was supposed to operate, until now. I had no idea that there was a lot of force pushing and pulling the filament along the feed path to the extruder, until now. I did all that I could to reduce friction so that the filament would glide along the delicate MMU. I’ve cleaned tons of particles left behind by the idler gears, which should be able to push a nail into the wall. But that is where finally, I found out what the problem was.

The idler was off-center, twisted or something of that nature giving me all kinds of errors at different times. I found that out as I was cleaning the gears with the power off when I moved the idler I noticed something. The idler motor wobbled whenever I moved the idler, a small amount but there it was moving the idler a little as it was rotated above and below as well is along the natural axis. That sent all kinds of alarm bells off to me as I grappled with the significance of that wobble. Adjusting the position and re-tightening everything was of no use, the problem was still there. I fixed the problem after getting a non-help from the chat with the Prusa technician.

When I called them the person that took my problem he asked me to submit a first layer picture, I told him the problem was with the MMU. He then told me to send him a video, I tried but this time the filament fed adequately Murphy’s Law. As soon as I shut down the chat there was no good feed from the unit.

That is when I made the decision to avoid the tech and print an idler, after all with my 0.6mm nozzle in less than three hours I’d have my part. Now I only have black PETG so It would have to do since I don’t have the Prusa Orange. I printed the part, removed the old idler and put it all back together. To my surprise as I tested each of the filament rows that the MMU could almost pull the printer over without any noise, simply power. I didn’t realize how the MMU was supposed to perform so I figured that it was a very delicate part of the printer. Well after two and a half months I now know what I was missing.

Just a note, I used the gyroid fill as opposed to the grid fill recommended by Prusa in hopes that this would ensure that the idler was perfectly round. I don’t know; however, I do feel as if that was the right decision.

If you are having problems, and the MMU doesn’t pull the filament through properly or one or more of the paths aren’t operational, then perhaps there is a problem with the idler. The test is simple, with the steppers off or the unit power turned off, watch the left side of the idler assembly. The motor should not move in any direction with the exception of its axis period.

I have contacted tech support at least four times on this issue and they have had me checking electrical connections or the adjustments of the tensioner screws. The problem is fixed and as such, I am posting this in the forum to aid anyone frustrated by the MMU not operating properly.


Stay safe and healthy, Phil

Posted : 30/03/2020 12:45 pm
Myf liked
Trusted Member
RE: MMU2S idler problems

Yes. This was it.  

But even after reading this post I didn't quite get what Phil was trying to say, I had to think of it myself as I was about to reprint my idler.  But it looked fine. Then it hit me this is what he was saying:

Make sure your idler motor is mounted so is forces the idler barrel & therefor the idler bearings towards the bond tech pullies, thus pushing the filament evenly from insert 1-5.  It has wiggle room and my wiggle loose or simple not be installed with the proper shift causing your barrel to have less pressure a filament 1 compared to filament 5.  Move the motor changes the angle of the barrel.

Spent the better half of a day on this, which isn't bad compared to Phils story above, but it was easily avoidable.

My issue was filament 1 stopped loading properly. I forced it through but it still wouldn't continue to the second sensor, so I though it was something else.  I was sure it was the board.

The best way to fix this is remove the board cover so it exposes the 2 hidden motor mount screws.  Loosen all 4 motor mount screws, then close the mmu (you might have to watch the clearance of the two inner screws you just loosened, they will block it from closing. Now push the loose motor (with the MMU closed) towards the rest of the MMU (this forces the entire side of the barrel downward/forward) and tighten the two motor screws you have access to-the ones you have to use the round end of the Allen tool for.  Do this while forcing the motor as hard as you can.  Now open the MMU door and tighten the other two motor mounts. 

I'm back baby, printing again. 

I'm going outside.

Thanks Phil!


The idler 

Posted : 15/05/2022 12:21 am
Myf liked