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MMU2 Resetting Mid-Print  

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cjbaar
(@cjbaar)
Active Member
MMU2 Resetting Mid-Print

I have run into more issues than I can count with the MMU2. Many have been solved with recent hardware and firmware updates, but recently I have a new one that is causing print problems. It seems that when getting ready to unload filament during a tool change, the MMU resets. The lights all flash, and the cylinder does it's usual startup of running itself into the back wall about 20 times. After that, the MMU attempts to retract the filament, however there is one major problem... the extruder gears have stopped entirely, and still have the filament trapped. This causes the MMU to just strip out the filament, and the unload eventually times out and fails. The majority of the time, I seem to be able to recover the print manually, but it takes quite a bit of unwanted force to yank the filament out from the extruder.

Has anyone else run into this issue? The manual says that if all lights are flashing, the MMU is not getting enough power. Just to be safe, I have replaced the power lines directly back to the power supply (bypassing the einsy board connectors) with 16-gauge wire, but the issue is still occurring. I am unsure why, if the MMU needs that much current, the lines are terminated to the tiny jst-style connector.

This topic was modified 3 years ago by cjbaar
Posted : 26/04/2019 3:35 am
jeffrey.j2
(@jeffrey-j2)
Active Member
RE: MMU2 Resetting Mid-Print

I am about to remove my MMU2.  It is more trouble than it was worth.  Failed filament loads, retraction issues with filament, thats just the preliminary problems.  Very experimental and I have to babysit the machine more than ever before even with manual color changes.  Coupled with the upgraded extruder and fan reducing temp of nozzle to point of fail is frustrating.  Got the sock but the SUPER delicate wires on the heat probe have failed and I have max temp indicator.  With my old eyes I need high powered magnification with about 10k lumens just to see the damn wires! LOL   

OK - tear down number 3 to occur to fix the hot end and remove MMU.

Posted : 28/04/2019 6:28 pm
cjbaar
(@cjbaar)
Active Member
Topic starter answered:
RE: MMU2 Resetting Mid-Print

Yeah, I feel your pain. In many ways it seems like we paid money to be beta testers. I don't like starting a 20-hour print before bed, and wake up to find that it failed an hour in. I am currently making prints with only a handful of tool changes (2-3 in a 5-hour print), and it seems like I am having this issue almost 75% of the time.

Posted : 28/04/2019 10:11 pm
Saiz
 Saiz
(@saiz)
Eminent Member
RE: MMU2 Resetting Mid-Print

I’ve had this issue plaguing my mmu2 for months. It will load fine randomly before a print starts, but as soon as you start a print it will do what you are describing. It took me awhile to finally get it on video. Prusa support wasn’t very helpful until I had a video of it. After that we went through a few more troubleshooting steps. They decided they thought my finda was malfunctioning. But I had already replaced my finda twice and the issue persisted. They finally sent me a replacement board for my mmu2 last week, it arrives today. Hopefully this issue is resolved with the new control board. I have a recording of the issue if you want the link to compare.

Posted : 30/04/2019 4:13 pm
vintagepc
(@vintagepc)
RE: MMU2 Resetting Mid-Print

Has anyone else run into this issue? The manual says that if all lights are flashing, the MMU is not getting enough power. Just to be safe, I have replaced the power lines directly back to the power supply (bypassing the einsy board connectors) with 16-gauge wire, but the issue is still occurring. I am unsure why, if the MMU needs that much current, the lines are terminated to the tiny jst-style connector.

This sounds almost like the PSU is underdelivering... moving the connector won't help. Maybe try swapping which supply line you are tapping for the MMU? (e.g. heatbed vs einsy power). If that fails, a separate 24v supply for the unit might be an interesting test...

Posted : 30/04/2019 4:24 pm
cjbaar
(@cjbaar)
Active Member
Topic starter answered:
RE: MMU2 Resetting Mid-Print

Thanks all for the additional input. I have thought about trying a separate PS. I don't think I have anything 24V on-hand, but I will look around. Whatever is causing the issue, however, I still feel like it comes to down to a potential bug in the main firmware itself (not the MMU). When this happens, the printer does nothing to resolve it. The extruder, for whatever reason, is failing to unload the filament completely. The new IR sensor is clearly triggered, and the printer should be aware that the filament is not properly unloading and should be running the gears in reverse. Even though the MMU is (apparently) suffering from a power issue, it seems to recover OK, and I think the print would continue fine if the printer was unloading.

@rlobbins, would love to see your video 🙂

Posted : 30/04/2019 5:11 pm
ad.lamy
(@ad-lamy)
Estimable Member
RE: MMU2 Resetting Mid-Print

Was a time I suspected also the PSU to be responsible of mid print failures, I contacted the tech staff for that and they ask me to control the PSU voltage in the support menu, I had 23,8v on both pwr and bed during print with MMU2, they told me the voltage is a bit low but in the tolerance values, they advise me to re-flash the mmu, since I had no more issues.

Posted : 03/05/2019 7:32 am
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