MMU2s wont load filament after cutting, now stuck in a loop  

RE: MMU2s wont load filament after cutting, now stuck in a loop

Did you order a new board yet. Very much like to know if that is the problem or not. Right now I'm so pissed at the MMU that I'm ready the rip it off and smash it.

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Yup, it is with a big order so it hasn't shipped yet. I'll return with results. I know these sensors and the setup for the MMU2S need to be almost exact what the assembly instructions say but I swear this is something else. My MMU2S randomly goes haywire and lights flash and it either won't unload the filament or it stops mid print to change the filament when its not supposed to. I've the modified selector installed(with the magnet) and have re-flashed  the board and calibrated too many times lately. I have 2 new Bondtech Extruders that I am going to install sometime soon I suppose.  But I need to print our the filament sensor mod for that and do a little more reading up on how to get that to work with the MMU2S. Not that I expect anyone to invest in new bondtech extruders. I'll do the basic install with the new board and see if that works before the upgrades that I am talking about.   

*I get the frustration. I'm even having issues printing single with the mmu2s. TBC...

RE: MMU2s wont load filament after cutting, now stuck in a loop

I DO NOT UNDERSTAND IT!!!! I haven't changes ANYTHING and all of a sudden I'm back to getting the ol' MMU2S unloading circle of death!!!!! I do not believe a new board is going to fix this. I don't have ANY idea on what can fix this. Words cannot express my aggravation or disappointment. I know others have success with this and I at one time did too but this is pathetic. 

RE: MMU2s wont load filament after cutting, now stuck in a loop

This has turned into a rage venting thread for me.  I do want to mention that my Mini+'s are still the best printers I've ever purchased. These things are just always on point. Now back to the issue at hand. 

RE: MMU2s wont load filament after cutting, now stuck in a loop

Sounds like yall have a lot going on but if you're still having the power issues you can always use the included USB cable for MMU flashing to connect the MMU's usb port into a usb hub/connector that also plugs into a wall/computer for some extra 5v juice. Just also remember to unplug it when you turn off the base printer or it stays on.

Loading/unloading loops can mean sensor miscalibration, or the pathing of the filament simply isn't going as it should: curving off and not hitting the gear teeth/hotend ptfe tube before/after the extruder gears respectively; fat tips getting stuck at any point; filament bites resulting in zero actual force transference; etc. It could be a million different things and you just have to painstakingly figure it out. But once you do you'll have another tool under your belt for MMU shenanigans.

I've also run into a few softlock incidents with Prusa's firmware and because of that have switched to the TZB firmware which, at the very least, fixed the softlock issue and is also being updated along with the base printer's firmware updates.

I also don't use any buffer 'system', needless added complexity imo. The most I'd do if you have all 5 in a close proximity row would be some cardboard between the spools to prevent potential tangling if even. The filament will find its way.

Also never used the cutter. Sometimes it seems like it would be great to just auto chop bad tips but it's always better if you can figure out how to fix the tips themselves. Latest issue I stomped was the tips of filament getting too fat/blunt to feed/unload correctly and the fix was raising temps and lowering cooling moves. And even that fix is a seasonal thing because I've noticed differences in printing during a warm vs cold season since I don't 24/7 climate control my room like an office building.

RE: MMU2s wont load filament after cutting, now stuck in a loop

Hey thanks. Yea you are right about the sensor calibration. Here I am almost 2 weeks later with some decent news. I've finally completed a multi material print on the machine that is giving me sad nights. Now to be fair I've modded the heck out of it. I've changed the selector to the one mentioned above, I've changed out the ptfe insert in the back of the MMU2S for one that has P4M10 fittings, I've added the RMU buffer, and I've just finished adding the Bondtech extruder they offer. I'm also testing a diamond cut nozzle. So here's what I think is true. The MMU2S works out of the box, its just really finicky. When something doesn't work the symptoms are things you have to get used to seeing. If the machine is repeating loading and unloading yes this most likely is something to do with the IR filament sensor -and knowing that there are things that cause the sensor to misbehave like stringy tips or it not being calibrated like @Baconfase said. Its frustrating yes but I continued to read up on the same issues many people have had and continued to debug them. I have 2 MMU2S printing and one is stock and the other is the modded one I mentioned here. They are both printing multi-material models. I still might have to tweak something here and there but I have it working. I will note that I am waiting to receive my Rambo board for the MMU2S and I may or may not try replacing that. The only way I'll try that is if the MMU2S starts acting a fool and doing things like loading on the wrong filament selector or when it gives the flashing light show for no reason or something like that. I'm also a fan of Chris's Basement. I'm sure many know who I mean but if you don't go check him out. He has some great content pertaining to Prusa printers. Ok -one print almost down as I type this, let's see if I don't have to return with bad news.    

RE: MMU2s wont load filament after cutting, now stuck in a loop

HAHAHAHAHAHAHAH!!!! As soon as I left that post I turn around and see the dancing lights. The MMU2S is literally driving me crazy.

RE: MMU2s wont load filament after cutting, now stuck in a loop

It can't be the settings or calibration at this point right? I mean it does all these weird gltchy things like the flashing light show and then the idler pulley randomly changes the filament isle leaving where the filament  stops being sent to the extruder where it stops extruding. And then when I fix that and try a reprint I'm stuck dealing the idler pulley not sitting on the correct filament lane. I'll re-flash yet again. I'm still waiting for the new board to get delivered I'm just venting my EXTREME confusion on why this board is misbehaving in such ways. The other MMU2S I have does  not have any of these issues. 

RE: MMU2s wont load filament after cutting, now stuck in a loop

Maybe I am wrong or I missed something, but if you have unloading issues, I would focus on that. If you don't get reproducible problem free loading/unloading this causes a whole rat tail of problems. It is key to figuring out what your primary issue is. Often, all the other problems go away by simply solving that one and if they don't you'd be able to identify a new primary issue and try resolving that one. Usually it is less things in the end you really need to resolve than it appeared in the beginning. 

Getting back to your issues. What is the cause of your unloading issues? 
Question one: How do your tips look like? Are they nice and without strings? Are they too big for the tube, ie can only move with extreme amounts of friction?
Question two: When unloading fails, where does it fail exactly? Does it get stuck in the middle of the tube connecting Extruder with the MMU? Or does it fail elsewhere?

When all lights are flashing at my MMU it always has been because the resistance for moving the selector was too high, usually because Filament was still blocking the path, strings were blocking something etc., 

PS: Resetting the MMU is just and emergency measure, even if you can resolve the issue seemingly with it, I had only troubles afterwards, something is getting seriously messed up when you do that and all sorts of funky stuff can happen subsequently. If you can't get an MMU print done without pressing the hidden reset button, you need to resolve the underlying problem that causes your need for resetting mid-print not the myriad of problems possibly caused as a consequence of resetting mid-print (selecting wrong colour, trying to move to a different filament when the previous one is still loaded etc). 

PPS: Of course, it is entirely possible that non of these issues mentioned above are what truly causes you problems, but that's what I would check or consider. 

RE: MMU2s wont load filament after cutting, now stuck in a loop

One more thought about unloading. Strings can mess up your filament detector in the MMU and cause false positive signals. It sucks that one can not operate the printer screen once the MMU goes into error mode but before it does, one can check in the "Support" section the sensor signal (0 or 1). Or did I understand it wrong and your MMU is not merely getting stuck in unloading but never even enters error mode? That would be odd as the MMU should give up after several failed unloading attempts and strike until you manually intervene. 

Given that you have already the magnet sensor, does that mean you have that variant which is actually half open and accessible from the outside? I have that one as I really hated to have to disassemble the whole thing just because I got it messed up with strings for one reason or the other. 

RE: MMU2s wont load filament after cutting, now stuck in a loop

    Hey thanks for the talk. Yea you're right about isolating one issue at a time. I was having the unloading issue(and I thought I mentioned that I fixed that in this long word jumbled thread). So like so many have said in other posts that the unloading issue is usually an issue with the IR sensor. It was at that point when I was in the process of swapping out my extruder for the Bondtech extruder upgrade.

    But before swapping them out I was able to get the stock extruder(the IR sensor) to properly read the filament. At that point I was no longer getting the unloading circle of death. All the while I would get these random spouts of flashing lights or the selector being at the wrong filament lane. It wasn't always doing that(flashing lights, wrong selector) and it was quite random. 

    So here is where I am at, the last print went about 30% in and then stopped extruding. This is something I have tweaked now and I think that won't be an issue(someone in other posts said that it would be the tension screws on the MMU2S are too tight -So I've slightly decreased the tension on those and adjusted that but also increased the extruder tension on the Bondtech a little bit and it looks good so far).

    So the last issues I faced was the MMU2S selector going to the wrong filament. That is the issue I faced last. But after a couple power off/power on cycles and a clean cut tip the MMU2S was back to the correct placement. I guess I have a difficult time understanding the relationship between the  selector going to the wrong filament and whatever is causing that issue.

    So again thanks -I honestly need someone to stop me and get me back grounded to the step-by-step approach of debugging.  Sometimes I'm run-and-gun type of process and we know how that can and mostly goes. 

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I had wrong selector issues too, the flashing lights might be merely a consequence of that. The issue in my case (and it was in the end my main issue) was that the maggot screw of the selector wheel loosened slightly, just to the extend that in the beginning after the startup calibration, the selector was still right but after a number of changes it slipped sufficiently that the filament wasn't gripped properly anymore as the counter wheel was not correctly in place.

Maybe that was just me but if you haven't done so already check if that selector wheel is sitting tight and can't be turned without turning also the motor and that there isn't even the hint of slipping. You can also look very closely at the selector wheel when the MMU is switching material. Does it move as it is supposed to, are the gears always in place?

In my case the crazy mixed up stuff always only happened after an initial failure of something that wasn't supposed to happen and the randomness of the start was caused by the not entirely reproducible adding up effect of tiny amounts of slipping. I figured it out when the slipping got bad enough that it become more visible and the successful number of changes was approaching single digits each print.

Yes two pitfalls of the MMU are the tightening of the screws of the MMU and also overtightening the extruder gears. That's something one needs to get a feeling for to get it right.

PS: It is easier if the error is happening often enough that one can catch it live as it starts by observing the print and the actions of the MMU and the printer.

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I am having the same/similar problem.  Slow flashing red light = problem during load.  I decided to just tackle this and work on getting a successful LOAD TO NOZZLE in the spirit of trying to deal with one problem as a time.  Start the printer with the filament just sticking out a bit looking to be cut.  Ask for Load To Nozzle.  Looking into the MMU I see the idler rotating into position to pinch the filament into the drive gear.  As soon as it is in place the drive gear stops rotating.  There is a pause and then the idler backs off leaving the filament free and the drive gear resumes turning in the forward/loading direction.  It repeats the process several more times and then tells me the MMU needs attention.  Any thoughts?

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I always load filament to the MMU using the 3 buttons on the MMU. Press the right button after start up and the MMU should do the calbration move. When that's done, move the selector to the correct position, press the centre button until the red light is blinking. Then manually feed the filament into the MMU until you feel that it is pulling it in. If you don't feel that, your tip is being caught up before the gears. If it does pull the filament in, watch what is happening at the MMU, does it move it to the filament sensor and then pulls it back and change from red blinking to constant green? If so, then the error is not at the basics of loading. What you can then try is if the idler is not engaged, is it possible to manually push the filament without large friction all the way to the extruder? If so, excessive friction isn't your issue either. Have a look then at Support>Sensors If you repeat all of the above, does the Filament sensor show what it is supposed to show ("0" unless there is filament in there). 

If all of that looks fine but the problem persists, can you try it, if you simply have no filament loaded and it is just pushing air in reality? Does the idler engage and immediately disengage as well? If not, take a piece of filament and as soon as it engages and insert it from the other side until you hit the ball of the filament sensor and turn it from 0 to 1. (check it if the reading really changes). The MMU should then believe that it is really loading. The loading would still fail eventually because the filament sensor in the extruder won't register anything. If you want to fake the cycle in theory, you can insert another piece of filament at the extruder to trigger that senstor too. If you do the entire "fake"-cycle, the MMU should be satisfied and turn to green. Do you get as far, or where does it fail? And what is the status of the two sensors when it fails?

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PS: You don't want the filament to be cut. The filament should not be sticking out at all but be properly pre-loaded. It will then rest just at the gears so that it can be moved by the MMU but doesn't stick out so that it doesn't block the selector. The cutting is a feature which is rather intended against strings but really if you want a smooth operating MMU you should try to have as string free operation as possible. 

RE: MMU2s wont load filament after cutting, now stuck in a loop

Thank you Most Estimable Member Thejiral.  I have a better understanding of the sequence for loading.

When I power up the idler rotates and there is a series of clicks.  It stops with the wheel over filament 2 but the green light is on 1.  I press the right button and the lights flash, the selector moves to the right then left (making noises) and stops on 2 with the light on 2 and idler wheel sitting over #2 groove.  I then pressed the middle button to initiate load, fed the filament in.  It caught, pulled in and retracted with the green light on.

Next was to select load to nozzle from the menu.  It heated, asked me what filament, rotated the idler arm back so #1 was in contact with its filament and started turning the filament drive gear.  Of course the filament went nowhere.  Then the light slowly flashed, the filament drive gear stopped turning  and the idler arm rotated back so it covered #2 again.  Pressing the middle button again initiates the same sequence and the same error.  It looks like it is confused about which filament to load.

Thank you for your help.

RE: MMU2s wont load filament after cutting, now stuck in a loop

Well, I prepared to take a video of the strange behavior and everything worked perfectly.  I just let it sit for a couple of days.  And I got away from it also.  I guess we came to a mutual understanding.  🙂