MMU MCU Error #04306 (MMU) | Prusa Knowledge Base

What happened?

The Main Control Unit on the MMU control board has detected a power-related issue.

How to fix it?

Verify all the cables are in good condition and all the connections are stable.

Do not move, connect or disconnect the cables while the printer is on!

In case the issue persists, contact our Customer support.

8 comments

VBauerova

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5 months ago

This error occured on my MMU2S after cca 2 years of printing, it was coming back even after separating the two cables and cleaning the contacts. Just came across this "hack" and I'm dropping it here for future fellow-sufferers:https://youtu.be/JAWqIH_U66s?si=LUZmsJ8fk_z3WLc2&t=1136

HarrySatt

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11 months ago

I get the MMU MCU Error #04306. It occures frequently after update to last revision of MMU firmware (MMU2S). I see that I have to fidle around with some wires but is that real. Nothing had changend in the hardware only the firmware was updated. Is there a fix on the way or do I have to live with that. It is a bit annoying, by the best.
Now I am told I have to upgrade to MMU3 because of firmware not working. Curious.

David B.

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11 months ago

Hi! There is no fix on the way. It is a hardware issue. MMU3 upgrade solves it. Prusa used to offer a free MMU3 upgrade voucher to the users having this issue persisting, till the end of the last year. You can try to reach out to the support to see if they might somehow help you - but fidding with the cable usually is not a proper long-term solution.

cschmehr

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11 months ago

Same error here. Separating the cables as shown above solved the problem. I'm a bit frustrated that this error occurred after a firmware update and you need to dig into the comments section to find out that it is an known issue. Would be nice to highlight this directly in the help article. Would have saved me a lot of time figuring out what's going on.

AudienceOfOne

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about 1 year ago

I will try to post the picture here. When i tired to add in my post above, it took over the entire post: (sorry the picture did not post, but if you chat with tech support i would assume you can get the picture. will mostmaybe this link will work:https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fcdn.livechat-files.com%2Fapi%2Ffile%2Flc%2Fatt%2F9644675%2F4ade6ef91d2dec99186d9be61b40aa53%2Fimage.png&data=05%7C02%7C%7Ce0938bff70634118d7be08dc01d9ed56%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638387282703523549%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=2391nnJd%2BJWGbgH6Zc4bEsO4p2mwrcSKXwq5Q%2Bvi0Ew%3D&reserved=0

David B.

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about 1 year ago

Hi! This might work because you "refreshed" the loose connection in the cables by moving them. This is probably not a good long-term solution though. In case the MCU error comes back, try to clean the connectors. If nothing helps to get rid of the issue entirely, contact support. They might be able to provide you with a MMU3 upgrade voucher till the end of this year.

AudienceOfOne

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about 1 year ago

Could be, but i have been successfully printing for 2 days without issue. I had wiggled / adjusted the two connectors prior to seperating the wires and still encountered the issue - IIRC.BTW, the latest MMU2 firmware is awesome. I had all sorts of issues with my MMU2s with the old firmware. It worked for a few months, then I encountered all sorts of issue getting filament to load where i mainly encountered the filament grinding at the MMU2. After the upgrade I have not encountered this issue at all.

AudienceOfOne

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about 1 year ago

I have an MK3s+ with an MMU2s and just upgraded each to the latest firmware. After that, I was encountering the issue above quite often. Today I chatted with tech support and he gave me the following suggestion and it worked for me ...
The second one being separating the signal from the power cables within the textile sleeve.
This solution worked for me. I will try to post the picture I got from tech support. After doing this, I had two successful 32 minute multicolor prints with at least 6 filament swaps.
I hope this helps.
btw, after the firmware and slicer update (2.7.1), I encounter an issue where the generated gcode would not run on my system with an MMU2s. I think support said this will be fixed in early 2024. My solution was to install Prusa Slicer 2.6.1 (i did this on a different computer), and the generated g-code run on my MMU2s equipped printer worked with out issue.

David B.

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about 1 year ago

The "gcode incomplete" error is a known bug. The G-codes are sill printable if you print the file anyway. It will be fixed in the next upcoming printer’s FW.