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Recovering from Wrong Selector Position  

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Hiro
 Hiro
(@hiro)
Active Member
Recovering from Wrong Selector Position

I have been printing for over 3 days (still at 50% completion) and within in that time, I had 6 user intervention.

1) Selector at wrong location - LED flashing 1 yet selector still at 3.  One time this happened where filament was not retracted all the way but the selector moved so that filament was still stuck in the selector while it moved.  After I removed the problem filament, I manually moved the selector by twisting the coil rod until it moved to right selector (not sure this is the right way to fix however).

2) Filament didn't retract all the way - had to press middle button repeatedly until filament retracted.  I also noticed that the retracted filament had a deep extruder gear mark to a point it was almost torn off (I removed the filament and cut the problem area out).

I would like to know:

1) How to fix if the selector is at wrong location after some problem happens.

2) How can I prevent a teeth mark on the filament (I do make sure that the 2 tensioner screws are flushed against the plastic part (or just .1-.2mm below it).

Posted : 15/05/2019 12:59 pm
gnat
 gnat
(@gnat)
Noble Member
RE: Recovering from Wrong Selector Position

In one case resetting the MMU (just the MMU, not the printer) helped get the selector re-sorted. On a subsequent failure I stumbled on being able to move the selected back and forth by "double tapping" the left and right buttons.

For the grinding issue, make sure the tension on the cover isn't too tight, but I don't think you can fully stop it when the filament is stuck and it insists on still driving it.

MMU tips and troubleshooting
Posted : 15/05/2019 2:27 pm
Hiro
 Hiro
(@hiro)
Active Member
Topic starter answered:
RE: Recovering from Wrong Selector Position

One case this morning when I had a problem with selector

1) Selector was stuck at position 3, however, the LED was blinking on the position 1.

2) Hit reset button on MMU2 but the selector did not move beyond position 3 again.

3) Manually moved the coil rod so that selector moved to position 1, made sure that the filament moves through the selector freely.  Hit middle button, which changed the LED color from orange to alternating orange and green. Hit right button and it continued on it's way.

So in my case, hitting the reset button on MMU did not fix the issue.

It would be nice if we can have a option during the problem MMU problem to re-calibrate the selector position.

Posted : 15/05/2019 5:11 pm
ntdesign
(@ntdesign)
Reputable Member
RE: Recovering from Wrong Selector Position

You guys all have MK3s right? I ran into this issue yesterday and after trying everything else I bit the bullet and pressed reset on the MMU. Turns out on MK2.5 the whole printer resets and the print is dead due to lack of power loss recovery. Is this normal? Is that also what happens on the MK3?

Some more detail, maybe save somebody time in their diagnosis: Printer works fine, I have done some nice/long 2-color prints (using arbitrary combinations of channels to make sure everything works). I have had none of the problems other people report with the sensors and such (but still have terrible MMU1 nightmares, so made some modifications straight away). For single color I have just cut off one of the feeding PTFEs, and am not using the buffer (couple of spools worth of single color prints, all fine). Even PETG dual color prints fine. I always restart Slic3r after switching between single/multi modes because I noticed random weird behaviour at times (though it is possible I forgot it this time). The hickup happened with my first 4-color attempt, and seemed to be random (I'll try it again with the same gcode to see if it is reproducible). I wasn't there when it happened, but the blinking suggests an issue upon unload (according to the manual). What can I say, no threads, nothing in selector, free movement through the selector and nice tips throughout. I could not get the MMU to do anything, left/right buttons are ignored. Pressing the center button just prompted an unload attempt at channel 1 (which is where the selector was sitting, failed channel was no. 4). After the death of the print I could just powercycle the printer and all filaments loaded cleanly.

I have a see-through selector mod installed, so I could tell the steel ball was exactly where it was supposed to be (i.e. down and no crap beneath it). Otherwise I have only replaced all long PTFE with el cheapo 2mm ID stuff from FYSTEC, and added a bit more chamfer everywhere. Those measures solved all my initial problems with underextrusion/skipped layers/load fails. I am planning to do something like the pushfit mod on the backside PTFE inputs (stock solution is honestly just crap). Honestly a lot of my factory-printed parts should be stuck down someone's throat, it took a lot of filing and my original selector would have been unusable if I had installed it.

I am at a loss here, my only idea is a bug in Slic3r or the firmware.

Posted : 17/05/2019 4:59 pm
ntdesign
(@ntdesign)
Reputable Member
RE: Recovering from Wrong Selector Position

Edit, tried the same gcode again and it failed at the same spot. After reslicing it seemed to work normal (I still have reliability issues and cancelled after a few hours and about 5 user interventions). So apparently a Slic3r issue.

Posted : 20/05/2019 7:51 am
SpongyBob
(@spongybob)
Active Member
RE: Recovering from Wrong Selector Position

After 5 hours of printing for a very long print job (estimate 1 day)  I had to intervene 3 times for unload or load problems. On the last one, I also had the same problem of the led blinking for the wrong selector position. I have an MK3s and MMU2 and I bit the bullet and pressed the reset button. The printer was able to continue printing again, but since the selector was in the wrong position it thought that the first filament was the 5th and started printing with the wrong filament, when it went to switch the filaments again, it thought it was once again on the 5th filament and had a unload problem. For me the solution would have been to be able to move the selector to the correct filament. The left and right buttons only tried to unload the same filament (#5) which the selector wasn't on.

Is there a way to move the selector in the middle of the print job when it is having an unload error? I think the buttons are disabled from moving the selector because it thinks there is still a filament loaded, but we should have a way to override this 🙁

Posted : 05/07/2019 12:37 am
Jorge S
(@jorge-s)
Active Member
RE: Recovering from Wrong Selector Position

On the MK2.5 - hitting reset on the MMU2 will reset the printer, this is what I was advised.

"on the Mk2.5 and on the Mk2.5S there weren’t enough pins on the board/mmu connector. The solution to this was implementing software reset where the printer sends a reset command to the mmu. On those printers the reset lines of the mcu and mmu are tied together. That means if you reset one of them, they both reset."

There is currently a request on GitHub for a SW reset 

 

Also on MK2.5/S don't try removing the power connector to the MMU as the printer will restart as well(I have tried this)

 

In short on MMU2+2.5 if the MMU2 gets into the all flashing 5 R+G LEDs or in the wrong position, your print is finished.

Posted : 05/07/2019 4:00 pm
SpongyBob
(@spongybob)
Active Member
RE: Recovering from Wrong Selector Position

I think this is a issue that Prusa could address and find a working solution for. I don't see why there isn't a way to move the filament selector no matter what is going on. Since it seems this has happened to several users, loosing a print after many hours of printing is not a very acceptable outcome.

Posted : 05/07/2019 5:14 pm
Nikolai
(@nikolai)
Noble Member
RE: Recovering from Wrong Selector Position
Posted by: jorge.s4

In short on MMU2+2.5 if the MMU2 gets into the all flashing 5 R+G LEDs or in the wrong position, your print is finished.

That's a real bummer. The ability to reset the MMU2 on my MK3s  saved already couple prints.

I think PR should change the way MMU2 and MK2.5/3 interacts with each other. Resetting the MMU2 shouldn't be necessary at all. IMHO this is a current work around for a design flaw.

Often linked posts:
Going small with MMU2
Real Multi Material
My prints on Instagram

Posted : 05/07/2019 6:35 pm
SpongyBob
(@spongybob)
Active Member
RE: Recovering from Wrong Selector Position

Wait! 🤪 I think I figured out something that works at least for filament load errors. In the middle of restarting my 45 hour print, it failed 5 hours into it. I had a piece of filament stuck behind the selector because for some reason the selector was off from the filament by about 0.5mm--don't ask me why. The only way to get behind it was to rest the MMU. Once I reset it, I was able to move it left or right with the MMU buttons. So I moved it out of the way, cleared the jam and then re-positioned the selector in front of the last filament that it had the load problem with.  I then was able to restart the print and it used the current filament--which was the last load error and correct filament. 

I'm sure I'm gong to have other problems with loading and unloading over the next 40 hours, so I'll let you know if I figure out how to re-position the selector after having to reset the MMU on a unload error. Cross your fingers 

Posted : 05/07/2019 8:37 pm
SpongyBob
(@spongybob)
Active Member
RE: Recovering from Wrong Selector Position

Success! 😝 

I was able to reset the MMU2 (w/MK3s) in the middle of a print with an unload error. You can try using the normal unload fast flashing error fix method in the manual--that usually hasn't worked for me--but then if you have an MK3s, you can reset the MMU. Note what filament the idler body is down on so that you return the selector to. I thought last time the LED flashing wasn't where the idler body was positioned, but I could be wrong. In either case if the normal fast flashing LED fix doesn't work:

  1. Perform the MMU reset
  2. Clean out any jams or filament pieces causing the problem.
    • This can be done by using the left and right buttons on the MMU to move the selector back and forth to fix all filaments involved.
  3. Very Important! Make sure you move the selector back to the correct filament it was on when you reset the MMU.
  4. Press the printer knob/button and resume printing.

This has worked 3 times. For some reason one time, it actually ejected the filament and wanted me to reload a new filament.

Good Luck. It is very nerve racking to work on the MMU in the middle of a very large print. Each time I have done it (3 so far within 7 hours), I pray that the print will resume with the correct filament 😥 

Posted : 05/07/2019 10:57 pm
Nikolai
(@nikolai)
Noble Member
RE: Recovering from Wrong Selector Position
Posted by: spongybob1958

Good Luck. It is very nerve racking to work on the MMU in the middle of a very large print. Each time I have done it (3 so far within 7 hours), I pray that the print will resume with the correct filament 😥 

In this case make sure the carriage is sitting on the destination path. MK3 is not sending the select command again, so it pulls the filament which is currently selected.

Alternate solution is to remove the filament and let it fail with loading issue. Then "fix it" by putting the filament in and resume. In this case it is selecting the filament correct.

Often linked posts:
Going small with MMU2
Real Multi Material
My prints on Instagram

Posted : 05/07/2019 11:12 pm
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