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

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

Great! 

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

Thanks for all the info in this thread. I am having issues with one of my MMUs. It started with filament 1 not loading. I reprinted a new idler and that fixed it, but then I was having the issues with the 5 LEDs blinking. I did a lot of troubleshooting and contacted support and they said it is a signal cable, which they are sending me a new one of. I am having an issue though with the startup, where it doesn't seem like the drivers realize when something has hit the end of its movement, like the idler or selector. So it just sits there and rams for a bit, and then rotates back....unlike my other MMU without issues, which realizes it is at the limit and stops. I'll include a link of a video. The orange one is working, the black one is not.

iCloud Video

@pcweber is this one of the issues you were having? I'm thinking of taking mine apart and seeing if the selector moves freely like you were describing, since it seems you also had the same issue with the idler.

I pulled the signal cable from my working one and tested it on the non-working one and it didn't solve the problem. I also swapped boards, and that didn't seem to solve it either.

Thanks!

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

Posted by: @aake-e

This problem is comming back to me on a regular basis and when it does it doesnt really seem to help doing anything. MMU2S continues to flash with all leds after power on when doing the move to find position.

Not in Stealth mode(but I have tried it and it dont get better or worse).

Cables released and rescrewed confirming good contact quite some times now, but no joy.

Today I litterally torned the MMU2S from the mk3s. Not happy and I dont have the time to continue searching problem fixes for no gain.

 

I decided to try one more time, as I needed a multicolor print. 

I ended up changing the electronic board of the MMU2s after a lot of checks of the system. Now the worst problems lika flashing all red or all red/green is more or less gone. Still, I sometime get all five red/green flashing but it is not any bad conncetion, for sure.

So I now can use the MMU2s, but the loading/unloading fail every time with need for "MMU needs attention". 

Probably can adress this later but I actually do not see what should be wrong. The basic MK3s+ never fails, and has not done since I got it, about thre years ago and 180days of printing in the log.

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

Although this may not be it, I got bit by a intermittent filament sensor on the mmu having similar symptoms.

Sometimes this could happen if the IR sensor is not quite adjusted. I did the SMD LED mod on the extruder, here one can visibly see if the problem originates there.

Intermittent errors are the absolute worse problems to troubleshoot in any area. It sounds like this is the case.

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

pcweber got that straight.  Intermittent problems definitely suck.  It took me quit a while to get my MMU2 working smoothy enough to keep it installed.  I'm with him about the extruder LED mod.  Without it I would definitely have scrapped the MMU2.

I have 5 mods on my unit, three of which were absolutely necessary.

1.  The extruder LED mod. This is an absolute must in my opinion. The nicest looking version requires some soldering but I'm definitely glad I did it.

2.  I had to spend some serious time in multiple sessions drilling out the feed side filament paths.  This was quit disappointing to me because the installation manual proved completely inadequate in its description of where to focus you attentions.  Every time I put it back together I was convinced it was fixed.  But like so many others, I had still missed something.  It turned out there were 3 areas where the print quality caused problems and it wasn't obvious when I first assembled the unit, or the second, or the third.   Works great now.

3.  I had to add a cable strain relief and a travel path guide for the Finda probe cable, because mine failed multiple times where the cable enters the top of the probe.  This was because of the back and forth straining movements as the selector moves back and forth.  I had similar failures with my heat-bead thermistor. This was another random problem and was hard to locate because the probe worked occupationally, but you could easily make it fail by manipulating the cable at the top of the Finda. 

I also have a 5.2 v USB power supply plugged into the usb port on the MMu2, the 5.0v USB power supply didn't help.  This was necessary to prevent the 10 blinking lights of death.  The added USB power does make it work much better, but I'm not sure it's the only power problem.  My 24V power supply runs at about 23.6 VDC and there are there doesn't seem to be an adjustments to increase the value. I haven't opened the power supply to check for and internal adjustment, but I don't think there is one.   Its possible that some of the MMU's problems stem from the week main power supply as a root cause.  I'm not sure about that thought.

RE:

Well, pcweber and Lynn is defenitely on the right track.

The filament sensor seems to be intermittently broken. No led light for 1/0 any more.

After some fixing it actually works for now, and the printer ACTUALLY FINALLY seem to be doing what it is supposed to do. 

Probably I had two different broken parts( MMU PCB and FINDA) plus the 5V power issue on top.

Right now it works and it doesnt even show the 5V power issue.

Will get a new FINDA, and assure extra 5V supply if needed. 

Thanks for all effort to help in this thread 🙂 

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

Happy to help, and that the problem is resolved.

Personally I've never had to use an external power supply to make the mmu2s work. Perhaps the problem is binding of some movements requiring more current thus lowering the voltage. I had some binding of movement of the selector, I think the cutter had cut into the front ptfe section. I reprinted another and did some fine sanding, up to 3000+, giving a highly polished surface. The selector moves quite smoothly without the NEMA motor connected, I even rolled the screw by hand, no binding, no problem.

I modified the idler drum because the one that came with the MMU wobbled. https://www.prusaprinters.org/prints/19229-mmu2s-idler-improved-mounting-for-motor no cracked barrel. 

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

I have had this happen a couple of times lately also.. I am thinking mine is getting too hot in my heated enclosure. I ordered a small fan to test my theory.  

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

Hi guys,

Replied to the post long ago, had my theory about a sensor ageing and thus it's measured value fall outside of defined "good" data, thus triggering the error. Second theory was hair-crack in the MMU's PCB, which would trigger sporadic faults due thermal-expansion - though that wouldn't explain why a number of other users had the same problem... Also, I could not relate the problem to temperature.

In the very beginning I contacted support, the reaction was a mix of "we are not willing to grant you any warranty either way" and "have you tried to unplug and plug it in again?" - in other words, I was stone-walled by a first-level-supporter... Which reminded me awfully well to a similar situation: extruder-motor was shot, would not have enough power to push the filament in normal conditions. Support insisted it was user error or a bent/misassembled extruder assembly, requested fotos and videos of the error. After I purchased a new motor on my own and upon arrival removed the original motor, it came apparent that at least one bearing was shot... Well thanks for following up on the warranty I paid for...
After that, never had the motivation to follow up. On one hand it's a shame since at that time, my unit was still under warranty and upcoming rumours that MMU2 was regarded by Prusa as a fail and thus not really followed up and supported, it was leaving a bad taste in my mouht - after all, this was the reason I coughed the money up two years earlier... And on the other hand, I never was succesfull in printing soluble filaments due tip-forming, so I did not need it that urgent... It was just a shame that I could actually not use something for which I shelled-out quite some money in the way it promoted.

However, found some new motivation and gave it a shot by ordering a new PCB. After all, the price is not that high...
And today, when I was replacing it, I did notice three things:

1. They either revised the design or my original one was from a prototype-badge. Original one has all the soldering-pads soldered, lettering says "2018-04-04 rev 0.3", pads for connector P6 look like they were used for testing and whatever was there has been removed before shipping. New one has soldering-pads in gold, the whole unit looks more like a regular production unit, lettering says "2019-09 rev 0.4.4". This makes me wonder: Why are there so many revisions? What are the revisions of all of you guys having the problem as well? Maybe it could be related to that? If so, oh boy...
2. I notice element F1 being changed in value. To my identification this is a resettable fuse, tripping at 0,14A on the rev 0.3, but on rev 0.4.4 it has a tripping value of 0.2A. 
3. Element F2 has also changed in value. Being a resettable fuse as well, on rev 0.3 this was 0.75A and now on rev 0.4.4 it has become 1.5A...

Coming back to my original theory, being a sensor is ageing and falling out of spec.
What if...
Those original fuses were too tight in limits, leaving not enough headroom for normal variations in wide-spread applications, only working as intended in the most ideal situations? 
If that is the supply for control-circuit with the F1 and supply for the power-circuit with the F2, a tripping F2 would also trigger the very same fault which would be indicated by all LED flashing red-green...

I am intrigued...!
Will crank up my printing efforts, exercising the MMU with some multi-material prints - will report back whether the issue is gone or not.
In the mean-time, maybe you guys with the problem can check the revision you own? If they're all rev 0.3, we'll know what we're at. If they're all different, well, then at least we ruled this one out...

Below are pictures to make my point:

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

Interesting find! Mine is also a rev 0.3 board. It was pre-ordered when the device was announced. If I can just order a new board and resolve the issue I'll be down for that. I've been having trouble since the board was about a year old, but it is now way out of warranty. 

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

I also preordered when it was announced.

I did get a new board one week ago and tje MMU actually works now, first time it ”really” works since I got it. And I did put hundred hours and lot of research here, but it mostly did not work. 

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

I tried Prusa support advices by disconnecting all cables from the MMU2s, cleaning them and reconnecting them. I have also updated the firmware of my MK3s printer and MMU2s to the latest version (3.10.0 - 1.0.6).

I tried a lot of things. That took me a lot of time. The behavior is erratic. No fix seems to work. I suspected a faulty MMU2s board. Finaly I contacted Prusa support and this was the answer:

"In addition to what you've tried already, could you also perform a factory reset of the MM control board itself (not the printer), and let me know if it will help."

https://help.prusa3d.com/en/guide/service-menu-factory-reset_86232

I did it and "oh miracle" the problem was solved.

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

I have done this, and it only temporarily fixed my issue. Just like every other fix. It seems to work fine for a day or two.

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

While my unit was in warranty tech support replaced mine, I never checked the revision though. Works fine now, but sooner or later I'll need to replace the FINDA. It  gets erratic when I fiddle with the mmu2s. By moving the cable it works. 

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

I have also recent joined the red-green flashing club. This thread is a real treasure trove of information, thanks to all who shared their experience. I have not checked my board revision or voltages, but I'll start with firmware updates and work my way from there.

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

I have 2 MMU2S and by far and away the causeof most of my issues is the FINDA's when they're either not adjusted correctly or what I'm getting now is there must be breaks in the cables from use.  They will misread and this throws the MMU2S in to all sorts of trouble!  I've had to resort to a cable tie to fold the cable back on itself which works for now but they need replacing.

I really wish Prusa would explain what the root cause of the red/green lights are, what is the trigger.  This would be hepful.

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

The Red/Green flashing seems to be a power issue...there already is an revision of the control board with changed testable fuses...although I've not tried this, some users report swapping out the board for a new one seems to help...and it is tempting....also:

on GitHub a friendly user reported this: https://github.com/prusa3d/MM-control-2.0/issues/15

This error seems to also happen on the new board...so I'm tempted to try it, although I have an 0.3 revision...

I hope this error will be fixed...and that that will stop the resetting altogether...

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

Posted by: @cowboyhenk

The Red/Green flashing seems to be a power issue...there already is an revision of the control board with changed testable fuses...although I've not tried this, some users report swapping out the board for a new one seems to help...and it is tempting....also:

 

on GitHub a friendly user reported this: https://github.com/prusa3d/MM-control-2.0/issues/15

This error seems to also happen on the new board...so I'm tempted to try it, although I have an 0.3 revision...

I hope this error will be fixed...and that that will stop the resetting altogether...

thanks for this info, interesting but also would indicate not much is normal folk can do to resolve the issues.  If it is the power as described why is it often inconsistent with the reset? It can be fine for a while then whatever I do it resets.  Could temperature etc in the room be enough to play a part? The quality of the home power supply etc? 

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

Posted by: @guyh

thanks for this info, interesting but also would indicate not much is normal folk can do to resolve the issues.  If it is the power as described why is it often inconsistent with the reset? It can be fine for a while then whatever I do it resets.  Could temperature etc in the room be enough to play a part? The quality of the home power supply etc? 

If it’s really operating around 4.6V then there can be very non deterministic behavior. Depending on the load, temperature, cable position (magnetic fields) everything and nothing can happen any time because it’s operating on the hard edge of the specs. The voltage is never stable and always fluctuating.  For example 0.2V drop might do no harm to the Ensy but causing issues on the MMU.

RE:

...used the new board without any errors so far...

...but...

If I follow the posts and schematics on the github-thread, and if that information is true, it is REALLY an embarassing error by design...

Following the thoughts from there, why would you need a protection for reversed-polarity in our application? I'm seriously entertaining the thought of bridging that diode...

Got to break out my multimeter and do some measurements... 😉