brian.h38
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Joined: May 26, 2018 4:45 pm
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MMU Selector and Extruder Steppers Unresponsive Mid-Print

Jan 07, 2019 3:27 am

TLDR: Half way through a print my Selector, and Extruder steppers stop moving and stop responding. Resetting just the MMU results in incorrect behavior.

Hey all. So I got my MMU 2.0 working pretty well with my I3 MK3. Dialed in ramming, and made sure to eliminate extra friction for the filament path. All looks good and filament isn't chewed up or jamming. I had a single print of about 1200 color changes without any issue.

So I start up the printer again for a new object to print. Sliced with Slic3r with the same settings as the previous print and the same filament. About 2 hours in I saw rapid blinking lights indicating an unload wasn't successful. So I open it up, and all looks good. So I press the center button...and the pully stepper rotates but it doesn't push the filament out. I realize the stepper labeled "Extuder" on the MMU isn't in the right position, the Selector Stepper is on Filament 4, and Filament 4 is loaded, but the extruder barrel is on Filament 3. So I press the center button again but this time put filament into and out of the probe to make the MMU think it is unloading properly. It finishes the unload, then the LEDs change to position 1, then the pully stepper moves rapidly as if it were loading filament, but the selector stepper, and extruder stepper don't move at all...None of buttons appear to do anything other than spinning the pully stepper, the other two steppers don't ever move. I am able to manually push the Selector to Filament 1, and rotate the barrel to position 1 (should I be able to do this by the way?) then push the filament in all the way to the hot end and press the center button. It loads and prints a layer of that color then can't eject the filament again because the barrel freely moves and doesn't put force on the gear in the MMU. I even paused the print, manually unloaded the filament, and did long presses on the Left and Right buttons and all it id was change which LED was lit up but didn't move the Selector, or barrel. I tried unplugging and replugging the MMU resetting it and not the whole printer. I didn't pull Once it came back online all the steppers moved properly, but after I resumed the print the printer acted like it was in Single Extruder Mode and wasn't talking to the MMU properly.

Is there a way to reset just the MMU in a way that it will recover from? Is there a way to force the MMU to rehome?

I reset the printer, cleared the bed and tried again. This time it made it 4 hours in before the MMU stopped responding to position requests. Any suggestions? Should I reflash the firmware? Current Firmware 3.5.1.1-1788, MMU 1.0.3-212 printed from SD. Thanks.

brian.h38
Posts: 2
Joined: May 26, 2018 4:45 pm
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Re: MMU Selector and Extruder Steppers Unresponsive Mid-Print

Jan 12, 2019 5:14 pm

Well until this is fixed I did find a solution that allowed me to continue once it happened. So once I found the printer paused and telling me there was an unload failure, I would put filament into and out of the probe to convince it that it was working properly. The bed would heat up again and it would start what it thought was loading the filament by purging into the tower. As soon as it started resuming I would pause it again using the front control. I would then remove power to the MMU, and plug it back in. The easiest way I found was to unplug the second connector on the MMU, the one with only black and red wires in it. Once it was started up again I would use the controls to confirm that all the steppers were working again. Using the front control I would select to load a filament to the nozzle. Sometimes this menu wouldn't be there as the printer thought the MMU wasn't there any more, but after going into a few menus and coming back it was there. Once the proper filament was loaded, and the MMU seemed to be responding to requests from both control methods, I'd hit resume on the front control, and it would continue with loading the filament and purging. This happened twice in my last print which was 20 hours. A bit of a pain but glad I got something working again.

martin.h48
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Joined: Dec 20, 2017 6:31 pm
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Re: MMU Selector and Extruder Steppers Unresponsive Mid-Print

Jan 31, 2019 4:32 pm

I've been having the same issue without a resolution yet. I got so frustrated that I took the MMU2 off my MK3 and left it for about a month. I recently put it back on and have not had any luck resolving yet. I've checked all wires, flashed and factory reset the newest firmware for the MK3 and MMU2. The next thing I was thinking of trying was a 3rd party firmware since the issue does not seem to be hardware related.

rui.v
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Re: MMU Selector and Extruder Steppers Unresponsive Mid-Print

Feb 04, 2019 12:00 am

I can confirm had the same issue back in mid Jan, then the symptoms got worst, it would do more frequent then it would automatically fail as soon the printer stayed on idle long enough that the holding current would drop on all mmu stepper motors, during all this I checked my wiring for any loose connections couldn't find any evidence even spread the comm header pins from the printer board to the mmu wires same issue, I thought I had a dying board on my hands but when I reverted back to V3.5.0 (V1.0.2) the issues went away, that's been almost a month without issue. I didn't respond sooner but need time to confirm.

peter.l22
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Joined: Nov 11, 2017 2:38 am
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Location: Minneapolis, MN
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Re: MMU Selector and Extruder Steppers Unresponsive Mid-Print

Feb 10, 2019 5:00 pm

I think the new MMU firmware is supposed to address this issue.

I don't think they've found the root cause yet, but at least they're working on it. There's some condition which can cause the MMU steppers to de-energize mid-print. This is pretty much unrecoverable. It happens to me about once every 10,000 filament changes, but others have been seeing it a lot more often.

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