I found serious design error in MMU2 electronics hardware  

RE: I found serious design error in MMU2 electronics hardware

My MMU2S started off working great and lately has been having issues with red flashing lights and filament changes.  Did the diode bypass and right now halfway through a 28 hour print and I havent had a single issue.   

Will post back once the print is completed...fingers crossed

If this works and prints correctly, I am sad that Prusa hasn't done anything over the course of two years to come up with a fix/workaround.  Instead they have indicated a new firmware will come (which hasn't arrived), considering that they are releasing the MMU3S soon, wonder if they really put much effort in fixing the MMU2s. 

RE: I found serious design error in MMU2 electronics hardware

Print just finished, had a flawless result.  Diode bypass has worked thus far. 

RE: I found serious design error in MMU2 electronics hardware

Thanks to the many who have posted on this forum topic. I hope it has been of help to you.

However now we have recent announcement from prusa  concerning Mk4 printer and MMU3 accessory including upgrade path from mk3S to mk4 and mmu2s to mmu3.

Among other fixes and improvement its expressly stated that MMU3 includes revamped communications and improved electronics. There is also improved wiring arrangement. So this would indicate that the issue covered by this forum has been addressed, and all thats required at least is for mmu2s users to upgrade to mmu3. The cost of $us89 seems reasonable.

So this leads me to the conclusion that this forum topic no longer has a purpose.

Cheers to all and happy printing.

RE: I found serious design error in MMU2 electronics hardware

yep, for 89 bucks there's almost nothing to lose.   earlier this week I ordered 2 of the MK3S+ -> Mk4 upgrade kits.  One of the two printers has the MMU2S on it and I'll probably upgrade to the MMU3 just to see if it's an improvement.  But I'm also a day one XL preorder for a 5 extruder XL and that's really what I'm going to count on for reliable multi-material prints(if it ever shows up lol).

RE: I found serious design error in MMU2 electronics hardware

Posted by: @pherz

Pragmatically speaking, what do we have to do to get Prusa to fix the problem on the new units and correct it on the legacy units we all have?

HMMM.  Well 8 months later, and we now have MMU3 just about to be released for ordering, with shipping in June/July.  But Prusa have prioritised Full Kits of MMU3 over MMU2S>MMU3 upgrade kits.  Its a petty annoyance, but seems to indicate that Prusa do not see the need to improve relationship with people who bought the MMU2S and have tolerated the issues that permeate it, some for a long time.  Many consider it a lemon product.

RE: I found serious design error in MMU2 electronics hardware

If the XL shows up in the next few weeks, I'll probably just convert the one MMU2S enabled MK3S to an MK4 when those kits arrive.  I consider the MMU to be a bit of a curiosity, and nothing more, I never EVER expect it to work.
The downsides to the MMU for me are(in no particular order):

- The mmu can't load flexible filament.  I know there are folks claim to have done it.  I print a good deal with flexibles and having to basically unplug the mmu and load the filament directly means I just don't even do it.  I have the other non-mmu MK3S that I do the tpu printing on.  But it's annoying that the mmu effectively gimps my printer for flexibles printing.
- The random failures due to the mmu losing it's mind.  Fortunately in most cases I can reset the mmu(but not the printer) and resume.  Because of the fact that the mmu and the printer are two loosely-coupled devices, it's really not surprising, but the author of this thread seems to have made a compelling argument that there is an actual flaw in the PCB design that causes the 5 all-color blinking condition that I've seen numerous times in the couple years I've owned the mmu.  The fact that the upgrade kit doesn't include a new board makes me even less likely to bother with the MMU2S -> MMU3. 
- The prints waste so much filament to purge especially if you're using solubles
- switching between different materials like petg often causes the adhesion issues on the purge block and in some cases it leaves a mess of filament strands that clump on the nozzle
- For soluble printing(the main reason I bought the thing), even prusa even says it's really intended only for PLA + PVA/BVOH.  Because the design is a big kludge, I get why.

I'm all but certain at this point that I'm just going to use the 5 extruder XL(if it ever shows up) and not even bother with the MMU at all.  

RE: I found serious design error in MMU2 electronics hardware

I still stand by my original posting to this thread. I do not believe Prusa should have ever sold the MMU2s as a finished product. Simply put it is UNRELIABLE and has never worked properly! Prusa should be embarrassed by its existence in its present form. Yes, I can easily afford the upgrade price and will upgrade my MMU2s. I hope it works as advertised.

I think it should be a free upgrade!

RE: I found serious design error in MMU2 electronics hardware

I'll buy just the electronic board. I modified my MMU2 and works very good

• shortened D1 diode
• new idler body https://www.printables.com/model/124431-idler-body-for-mmu2s-with-some-extra-features
• larger ptfe tubes
• tower mmu buffer https://www.printables.com/model/18340-prusa-mk3s-mmu2s-tower-print-buffer

RE: I found serious design error in MMU2 electronics hardware

The fact that the upgrade kit doesn't include a new board

Where do you get this idea? The product listing says it comes with “improved electronics.” You print your own plastic parts and keep your motors, and the firmware is a free download, so what else would there be?

RE: I found serious design error in MMU2 electronics hardware

From this link

https://forum.prusa3d.com/forum/original-prusa-i3-mmu3-general-discussion-announcements-and-releases/mmu3-proposed-changes-dound-great/#post-652877

Posted by: @dwineman

The fact that the upgrade kit doesn't include a new board

Where do you get this idea? The product listing says it comes with “improved electronics.” You print your own plastic parts and keep your motors, and the firmware is a free download, so what else would there be?

RE: I found serious design error in MMU2 electronics hardware

"The control board is the same, however there's an additional little board plugged in the ports of the power and signal cables that's to avoid the problem of miscommunication between the cables, which sometimes were causing power issues".

Ah, interesting. It sounds like the voltage problem has been addressed, then. The “loose coupling” has also been addressed by the firmware rewrite. As far as I know, the common issues that remain are mechanical, so I’m optimistic that the MMU3 will be a big improvement. They’ve also said that the new firmware will support the MMU2S, so you can get at least some of the benefit for free.

TPU will still be troublesome due to the nature of the loading mechanism, but that seems unavoidable on a single extruder. PETG and PLA not sticking to each other is a chemistry problem, not an MMU problem, but I sympathize.

Since you print flexibles often, you might try adding an MMU bypass switch to avoid the tedious process of unplugging it every time. I’ve done this mod and it works well.

RE: I found serious design error in MMU2 electronics hardware

Prusa could easily negate the need for this type of post by publishing details of what the full kit and upgrade kits comprise.But no, we have to wait …..

Even the mmu2s never had a proper description of how it works, which would have saved a lot of people a great deal of time working it out by trial and error.

I have to say that had I known the Mmu2S was so badly designed when I made purchase decision 18 months ago I’d probably have thought twice about it. All I wanted was a color print capability that works flawlessly just like the printer .

I just hope the MMU3 finally delivers against that hope.

. 

RE: I found serious design error in MMU2 electronics hardware

I heartily agree with most of your sentiments, however beg to differ on the electronics. Upgraded electronics is a major part of the upgrade as clearly stated in the release. but sadly we have no actual details of whats actually in the kit(s).

RE: I found serious design error in MMU2 electronics hardware

Posted by: @bryn51

So this leads me to the conclusion that this forum topic no longer has a purpose.

Cheers to all and happy printing.

 🙂 👍 It has a purpose as a resource for people with a MMU2 that are looking to improve it or people like me that still have not built it. But there is no value in continuing to add to it. In the beginning there was a lot of discussion by some very knowledgeable people on possible fixes/workarounds to what seemed to be a major contributor to failures. And people who tried the different solutions would post their results. This was one of the most informative and useful topic threads to follow. Then it was hijacked and derailed by <>, who posted about a completely different product and <> that wanted to we and bh about what Prusa Research should do. I will archive this thread( minus the <>) and use what information that I think will work and 'Thank You' to all that contributed in a meaningful way to this thread.

Kenn

RE: I found serious design error in MMU2 electronics hardware

MMU3 will not work on the MK3s board, so its not a fix... looked in to this

Posted by: @bryn51

Thanks to the many who have posted on this forum topic. I hope it has been of help to you.

However now we have recent announcement from prusa  concerning Mk4 printer and MMU3 accessory including upgrade path from mk3S to mk4 and mmu2s to mmu3.

Among other fixes and improvement its expressly stated that MMU3 includes revamped communications and improved electronics. There is also improved wiring arrangement. So this would indicate that the issue covered by this forum has been addressed, and all thats required at least is for mmu2s users to upgrade to mmu3. The cost of $us89 seems reasonable.

So this leads me to the conclusion that this forum topic no longer has a purpose.

Cheers to all and happy printing.

RE: I found serious design error in MMU2 electronics hardware

UPDATE to the question (as i timed out), what's the best (and safest long term) fix?

• Removing diode D1
• Installing a 24>5v DC converter? (which type as one seems to burn of as hear, like to avoid this).

RE: I found serious design error in MMU2 electronics hardware

I wonder why it is then,  that prusa say there are two slightly different versions of MMU3, one fir Mk3S+ and the other for MK4, the difference being connection to the extruder which are slightly different for each printer. 

RE: I found serious design error in MMU2 electronics hardware

Posted by: @griffcomm

UPDATE to the question (as i timed out), what's the best (and safest long term) fix?

• Removing diode D1
• Installing a 24>5v DC converter? (which type as one seems to burn of as hear, like to avoid this).

The best long-term fix is just to purchase the Mmu3 upgrade kit fir MMU2S, (mk3s+ version). 

RE: I found serious design error in MMU2 electronics hardware

Prusa had told me the MMU3 is not compatible with the MK3s, and this advice doesnt seem to go well with regards "fixing", as there appears to be a valid fix to add a new power method, with how many MMU2s units in the field the advice appears to be to scrap them?

RE: I found serious design error in MMU2 electronics hardware

Posted by: @griffcomm

UPDATE to the question (as i timed out), what's the best (and safest long term) fix?

• Removing diode D1
• Installing a 24>5v DC converter? (which type as one seems to burn of as hear, like to avoid this).

As stated before in this thread, my MMU2S works as advertised since I added the additional power supply.