MMU2S keeps resetting/Red & Green LED's flashing at once.  

RE: MMU2S keeps resetting/Red & Green LED's flashing at once.

Has anyone had a definitive solution to this? I am experiencing this with one of my MMUs. It will usually be on unload, either before or after it unloads the filament. I have 2 MMUs, one orange and one black. The orange one is experiencing the problems, here is what I’ve done so far, none of which have solved the problem. Both boards are the 0.4.4 revision with the latest firmware:

• Checked all wiring. Unplugged and plugged all back in.
• Reset EEPROM of MMU
• Plugged in a USB power supply.
• Swapped the control boards of the MMU between both printers

all the problems are on my orange MMU printer. Even after swapping, the problem still happened on that printer with the black MMU board on it. So next I think I will run a new cable, as I have a spare. Other than that, what’s next? I read in October Prusa was talking about a firmware update, but that hasn’t come out yet. This MMU has basically become unusable, so I’m hoping to have something rather than having to wait for an unknown ETA firmware update that might not fix it. 

RE: MMU2S keeps resetting/Red & Green LED's flashing at once.

 Mine gets STRANGER and STRANGER.   I use mine with only one filament now, but what I noticed is that for some reason the MMU 'cycles' or does something - WHILE THE PRINTER IS PRINTING- and there is no filament swapping by the MMU called for.  I'm printing on #4, and I can hear the MMU doing something- and all of a sudden, the indicator for slot 1 is lit, even though the selector hasn't moved (or even tried to move as far as I can tell) and it is still feeding through slot 4????  I just looked as it is printing and the barrel selector with the bearings is in the right spot for #4, eventhough #1 is lit?

Also, recently as I was going from menu to menu on the printer itself- the screen went blank for about 20 seconds, and then came back...

My sensors are working and the MMU filament sensor is fairly new...

I don't get it. I worked hard to get the mechanical gremlins- filament feeding and filament 'drive' through the MMU.

PRUSA talked about some MMU mods (maybe beyond firmware and teased hardware), but nothing so far. It would be awesome if they came out with something for us to work on over the holidays.  You know to keep Santa from giving them coal over the whole XL thing.

RE: MMU2S keeps resetting/Red & Green LED's flashing at once.

^^ Is the idler trying to move or the motor even moving? In that case you'd have loose grub screws. I don't think so but definitely good to check.
You may also check both sensors by manually inserting fillament and observing the sensor readings on the screen over some time, especially check if they stay consistently correct or show short fluctations once in a while. Just to be sure you've got no issue there either. 

To me it sounds as if you might have that undervoltage issue that is the subject of a huge thread here on the MMU2s forum. 

RE: MMU2S keeps resetting/Red & Green LED's flashing at once.

Thanks, I replaced the idler with a new PC one fairly recently- I don't think that is the problem, but after this print I'll put it throught its paces. 

It is more that the machine seems not to know where the selector is- and the weirdest thing is that it seems like it doesn't care?  The MMU used to slam both ends to make sure it was 'calibrated' to the correct feed, now when it boots, it doesn't do that.  Also when it is moving the selector, it sometimes gives up, blinks red/green at all positions.  It sometimes then starts over, but sometimes it doesn't.  It seems random.  I need to spend an hour with it and just do some feeds and changes and see if I can parse out what it happening.  I'll look at that low voltage issue, I think I remember reading that.  

I've been using my MINIs lately due to MMU anxiety, but I needed the extra space for a model house print for one of my son's classes.  Man, does that Mk3 lay down PETG nicely.  170x170x50mm models by each floor- 8-12 hour prints- but even my wife thought they looked good...

RE:

The reason I am mentioning the screws is because I had that issue and it took me weeks until I finally figured it out. If you just a tiny bit bit of slipping, the MMU can work perfectly fine for even dozens of material changes until the difference between real and target position gets so large that you start to get errors and hell brake loose with seemingly random moves. 

Also if you at any time press a reset during a print you usually can forget the print, it will confuse the MMU to no end. So reset is really only for resolving an issue that couldn't otherwise be resolved in the knowledge that it will most likely sacrifice the print. 

With what you write, you seem to have some other issues than this undervoltage thing I think. Have you cleaned the MMU, inlcuding the selection paths, gears etc from strings? They can partially block the selector or even the idler wheel. When you have too much resistence the MMU will throw light alarms and stop moving. When the printer is off, turn the helical gear of the selector to move the selector manually. Do you feel some blockade at some point?

An issue can be a loose selector blade. It can catch the other side and block the selector. I for my part removed it if I am not mistaken.

If your MMU is not doing the startup move at some point at least where it is finding the right end properly, you have an issue that needs to be resovled before it even make sense to do a lot of test printing. If you have no proper startup, the MMU doesn't know where it is and random looking errors are as good as guaranteed. 

RE:

PS: You said you replaced your idler with a PC one. You mean PC-CF? PC without CF has a horrible tendency to warp at such large pieces. Is the idler perfectly straight and not warped?

To be honest, I would not replace any MMU parts with non-PETG parts, not unless you have already a perfectly working MMU and have the desire to risk messing things up. If you have enclosure temperatures where the PETG is getting into trouble the MMU board might run amok long before. 

RE:

Posted by: @thejiral

PS: You said you replaced your idler with a PC one. You mean PC-CF? PC without CF has a horrible tendency to warp at such large pieces. Is the idler perfectly straight and not warped?

To be honest, I would not replace any MMU parts with non-PETG parts, not unless you have already a perfectly working MMU and have the desire to risk messing things up. If you have enclosure temperatures where the PETG is getting into trouble the MMU board might run amok long before. 

I had to replace the idler since it was cracked.

Sidebar- i had to tear apart my MMU to get the idler out of the ‘base’.  And those bolt heads that are accessed at a shallow angle are a screw up.  The MMU does not seem to be built to be serviced- and the idler is a part that IS going to fail.  Also- the bearings in the idler are not the usual bearings used in most things.  And I had to dremel the old idler to get the pins and bearings out. 

Just PC and there was some warping on the idler.  Getting the bearings and pins in was a PAIN.  The idler wasn’t that curved, it would spin on its center, but it really didn’t rock even thought it was ‘high-centered’ like a jeep on a rock.  Interesting, the bowing issue made me pay more attention to the engagement of the idler with the teeth on the drive.  I ended up having to shave down the housing near where the spring-ed bolts hold the top end down to get them to engage correctly- and I had all five feeding and loading and unloading perfectly.

So I only have filament loaded and tested in position 4.

Shutoff the machine.

Restart.

Printer boots up, and the MMU starts up. The selector gate never moves stays at four and the idler is also set for position 4, but when all started, the first button lights.

The left button will not move the selector/gate from position 4 or move the idler.

Press the right button and the MMU realizes that it isn’t in the correct position (?) and runs a right then left gate/selector zero, and the idler spins to position 2.  Press the right button and it moves to position 3, and then to position 4 where I can test the load with the center button….

I have a video, but I’m having issues getting into my youtube account to post it.

RE:

I assume you actually used some PC-Blend, Prusament or something similar. In any case, this could be one of the causes of your problems. You really want dimensional accuracy which is basically impossible with PC at a part of this size without professional actively heated chamber printers.

Even if your wheel spins freely, you simply have an incorrect geometry if the barrel is warped and with PC it will be. I would really stick with PETG. If you want something with stellar impact resistence and layer adhesion, have a look at PCTG. It is a bit softer than PETG though but at such a solide piece like the idler wheel it should be still rock solid. The original parts are printed rather rough, it helps if you reprint the part slow and with 0.1 mm layer height.

Assembly shouldn't be a problem regarding screws if you don't use excessive tightening in the wrong places. Actually the manual comments should warn you about where to be cautious regarding that in specific.

Regarding buttons. The left button doesn't do much for whatever reason as first command. You can press either the middle button or the right button to start the move to the right side and calibration of the selector. So much is normal. What isn't normal is that the MMU isn't calibrating already at the startup and finds the correction position with both selector and light. A common problem is that your selector is blocked or resistance is too high in movement.

Do you have the correct and neweset firmware of both, the Mk3s(+) and the MMU2s, installed?

Have you rechecked both filament sensors for not only correct but also consistently correct readings? This is in fact another very common reason for confused selector actions. It might be enough if you have occasional sensor reading glitches for just a blink of an eye to confuse the MMU.

RE: MMU2S keeps resetting/Red & Green LED's flashing at once.

PS: It should not be necessary to engage in massive sanding and redimensioning of parts. What I saw was that clearance for the idler bearings was to tight but that was primarily because the part is printed by Prusa at a rather rough resolution. So there some sanding was necessary to ensure friction free spinning. I also sanded the front facing the selector blade a bit but since I removed the blade this isn't of any much significance anymore.

RE: MMU2S keeps resetting/Red & Green LED's flashing at once.

I appreciate the effort, and I know a lot of people would recoil in horror the mods I've done to my MMU2S, but I am an early adopter and have been through all the BS with this POC.  I've been at this 10 years and I had Printrbots before this, so yes, I understand how to tweak these machines at the mechanical level. 

Six months ago I finally got it working after the idler (which is not designed right, if screw tension is that critical, and you are at the edge of PETG suitability, and it is a critical function, it really needs to be designed to be more robust.). Then it just started doing these random things.  Sensor work and are calibrated, I check them all the time.  That the MMU eventually calibrates the gate/selector and the idler moves with out issues means that it isn't a mechanical issue. 

I re-installed the firmware twice since the issues started coming up. If anything, the last update seemed to make things worse.

Mechanically it works fine.  I can load filament on all five and move from one to another, and then load to the extruder and unload and change fine.  20-30 changes, no problems.  Let it try to do itself for a print and it gets lost.

I THINK (can't remember) but I think the MMU has gone all blinky while the printer was printing.

And yes, I'm a little hacked that the XL isn't out yet.  I had this thing working earlier this year, then started having problems, and I was like- heck, I'll leave it alone and just use my XL over Christmas, surely they'll be out by then....

Now we've been promised work on the MMU since August it sounds like.  Prusa needs to learn to shut their pie holes until they are actually capable of something.  Learned that from an retired coworker. He never promised anything that he hadn't already done. 

So here we sit with a promise of the XL in one hand, an MMU update in the other  - and a printer that doesn't work.

RE:

Just sharing my ideas what could be the reason for the failure to correct locationing. You are there with your printer so of course you have a better insight what is going on. I am also not saying that the MMU doesn't have some design flaws, however it can work quite reliably once the initial trouble shooting is successful and it does so for 2 years now already in my case. 

I am not sure I got you correctly, if you do a startup, is it possible for you to load all 5 channels with filament using the MMU buttons only?

If the MMU goes all blinky during a print, when there isn't even filament changing to be done at all, I really can only think of sensor issues, undervoltage issues or a faulty MMU board as reasons. 

Have you contacted Prusa Live Chat already? If so, were they any help? 

PS: My MMU also did all sorts of crazy stuff in the beginning. In my case it was friction along the pathway, tube diameter of the MMU<->Extruder tube, a loose grub screw on the idler wheel and extruder sensor tolerances that were a tiny bit too much (so I extended the sensor lever by just a tiny bit for solid and correct readings). That and you need to set the two tensioning screws on top really to the right level without a lot to guide you to the correction position. 

RE: MMU2S keeps resetting/Red & Green LED's flashing at once.

PS: Damn time-out. Sorry, just saw that you already wrote that you can load all 5 channels manually. 

RE: MMU2S keeps resetting/Red & Green LED's flashing at once.

Prusa support told me to move the MMU power cables on the board one pair to the right, so they're connect to the middle two terminal screws. That made all my problems with flashing red/green LEDs on the MMU go away.

RE: MMU2S keeps resetting/Red & Green LED's flashing at once.

So this would supply power to the MMU from the Bed Power Input instead of the Power Input?

Aren't these a parallel  output in the PSU and not really separately regulated outputs?

I don't understand how this would have any effect?

RE: MMU2S keeps resetting/Red & Green LED's flashing at once.

I cannot speak to the reasons, only to the result -- it solved my problems.

RE: MMU2S keeps resetting/Red & Green LED's flashing at once.

I tried moving the MMU2 power supply from the original left connectors to the secondary Bed connectors and I still get the dreaded Red/Green Lights.

RE: MMU2S keeps resetting/Red & Green LED's flashing at once.

5.2V power supply fixed my all-lights-flashing-problem and additionally fixed some intermittent weirdness during the homing of the selector (sometimes it would not home like normal with two long and 3 short approaches to the right corner but do about a dozen very short ones - did not happen since the installation of the new power supply).

RE: MMU2S keeps resetting/Red & Green LED's flashing at once.

After reviewing lots of articles and comments from people I managed to get my MMU2S working.

I tried

1. different printable parts,
2. Upgrading to the latest firmware 1.0.6
3. Using a USB Mobile Phone charger to the USB Micro port of the MMU,
4. Swapping the cables,
5. Reaseating the Cables
6. Swapping with brand new cables.
7. Swapping the motors.
8. Factory resetting the MMU
9. Factory resetting the Mk3S.
10. Checking the Finda probe was working.
11. Downgrade the FW to an earlier version ie 1.0.5
12. Lastly I bought a Meanwell PSU 24v 10A and tried to wire the MMU directly.  Even though my Multimeter showed there was power, the MMU just did not come to life???

All the above led to the same 5 x red/green lights.

At the end all I needed to do was downgrade to 1.0.2  Problem was, I could not find that version on the Prusa Site or GitHub,  luckily it was included in a very old version of the MK3S firmware which is still on the Prusa webpage.

RE:

Moving forward, I am curious to see what is the differences between 1.0.6 and 1.0.2 MMU2S firmware.

I suspect there is some code that is stating the power supply.  Once I have reviewed both source FW files.

I might be able to come up with a modified 1.0.6a which will work with the existing Prusa FW, unlike the ZeroBeast which required both MK3 and MMU to be flashed with its own FW.

Will let you know.

RE: MMU2S keeps resetting/Red & Green LED's flashing at once.

While all the culprits mentioned will cause this blinking issue, the selector being interrupted is the one I see the most.  If anything interrupts the selector positioning OR the filament feed and the MMU *thinks* it's been interrupted, it gets confused and blinks all lights.  Mid-print, I've needed to disassemble the selector mechanism, on multiple occasions to correct this, then hit the mmu reset button to and force it to re-home.
Specific things I check for now are... Is there a plastic thread/hair or any debris on the drive screw? Or stuck in the selector thread/body? Did the mmu cut a filament tip and fail to clear it? Did a filament tip or other debris get caught in the 4 screw mounting holes just under the filament holes and the selector is caught there? Are the drive screw or guide rods just in need of lubricant? Did the mmu housing warp a little and the selector isn't homing properly? Is the cutting blade catching on anything as it slides past the filament holes?
The re-homing one was really frustrating. The ac went out in the office and I *think* the humidity spiked too and the mmu housing swelled just a fraction.  Whatever the reason, the selector locked up on the motor/right side causing it to home about 1-2mm shy of where it was supposed to and it just did the blinking routine no matter what else I did. 

I hope this helps!