MMU3 Firmware Version: N/A - Can't Do Upgrades
I have a Mk3.5S with an MMU3. I haven't used the MMU3 for a while, since it's been a nightmare to use in a humid region (filament threading and related issues). I'm making a print cabinet to solve the humidity issues and want to use it again. I just tried an update and it's a mess.
I went to the firmware pageand found two files that looked right to download:
prusa3d_fw_MMU3_3_0_3_MK35_MK35S_6_4_0.zip
and
prusa3d_fw_MMU3_3_0_4_MK35_MK35S_6_5_3.zip
The first file was listed under Firmware 6.4.0 (3.0.3) MK3.5S, MK3.5 November 25, 2025 and the 2nd file was listed under Firmware 6.5.3 (3.0.4) MK3.5, MK3.5S March 24, 2026. I felt like the title for that 2nd file was a bit ambiguous. Although it did specify the Mk3.5s as an applicable model, I thought it best to try the 6.4.0 version first, which did include an MMU3 update has well. So I downloaded it, unzipped it, put the two files (MK3.5_MK3.5S_firmware_6.4.0.bbf and MMU3_FW3.0.3+896.hex) on a USB drive and upgraded the printer. It worked and, honestly, I wish I had stopped there. When I checked the versions under Info, it looked right.
Then I downloaded the 2nd file and unpacked it. I saw that it had a file for the printer firmware and for the MMU3 as well (just like the older file). So I unzipped it. (Two files on it: MK3.5_MK3.5S_firmware_6.5.3.bbf and MMU3_FW3.0.4+936.hex.) I erased the USB drive, then put just those two files on it. That's when the problem started: I use a Mac and MacOS puts some invisible files on volumes, so when I reset the printer, it couldn't fine the file - it basically stayed in the "Looking for bbf file" forever. I searched and found. the issue about the invisible files. (Their names start with a dot, which means the OS doesn't usually display them to the user.) I got rid of them and tried it again.
This time the printer did flash the firmware update, but it didn't look like it did anything with the MMU. Then I got an error message that the MMU version was not compatible with the firmware version. My choices were to restart or disable the MMU.
I ended up downgrading the printer firmware to the earlier file, 6.4.0. When I looked under Info, it reported that firmware version, but for the MMU firmware, it reported it as N/A.
That leaves me with these main questions:
1. Why is it when I tried updating to 6.5.3, it didn't also update the MMU3 firmware? (I did have the MMU enabled.)
2. Why is the MMU now stuck at version N/A and what can I do to make sure it gets updated?
3. What do I need to do to get it to successfully upgrade to 6.5.3 and the accompanying MMU update (to 3.0.4 for the MMU)? Or is there a reason I shouldn't upgrade to that version?
RE: MMU3 Firmware Version: N/A - Can't Do Upgrades
@Tango Sounds to me like you are attempting to update the MMU3 via the printer. The MMU3 has its own USB connector, though.
I try to give answers to the best of my ability, but I am not a 3D printing pro by any means, and anything you do you do at your own risk. BTW: I have no food for…
RE: MMU3 Firmware Version: N/A - Can't Do Upgrades
@Tango Sounds to me like you are attempting to update the MMU3 via the printer. The MMU3 has its own USB connector, though.
I try to give answers to the best of my ability, but I am not a 3D printing pro by any means, and anything you do you do at your own risk. BTW: I have no food for…
RE: MMU3 Firmware Version: N/A - Can't Do Upgrades
@Tango Sounds to me like you are attempting to update the MMU3 via the printer. The MMU3 has its own USB connector, though.
I try to give answers to the best of my ability, but I am not a 3D printing pro by any means, and anything you do you do at your own risk. BTW: I have no food for…
RE: MMU3 Firmware Version: N/A - Can't Do Upgrades
@Tango - sounds to me like an attempt to update the MMU3 via the printer. The MMU3 has its own USB Type B connector and is updated directly. The MMU3 enablement in the printer is for the printer to recognize or not recognize the MMU (can't remember what the position needs to be for updating the printer firmware, but there's a manual for that.
I try to give answers to the best of my ability, but I am not a 3D printing pro by any means, and anything you do you do at your own risk. BTW: I have no food for…
RE: MMU3 Firmware Version: N/A - Can't Do Upgrades
@Tango - sounds to me like an attempt to update the MMU3 via the printer. The MMU3 has its own USB Type B connector and is updated directly. The MMU3 enablement in the printer is for the printer to recognize or not recognize the MMU (can't remember what the position needs to be for updating the printer firmware, but there's a manual for that.
I try to give answers to the best of my ability, but I am not a 3D printing pro by any means, and anything you do you do at your own risk. BTW: I have no food for…
RE: MMU3 Firmware Version: N/A - Can't Do Upgrades
@Tango - sounds to me like an attempt to update the MMU3 via the printer. The MMU3 has its own USB Type B connector and is updated directly. The MMU3 enablement in the printer is for the printer to recognize or not recognize the MMU (can't remember what the position needs to be for updating the printer firmware, but there's a manual for that.
I try to give answers to the best of my ability, but I am not a 3D printing pro by any means, and anything you do you do at your own risk. BTW: I have no food for…
RE: MMU3 Firmware Version: N/A - Can't Do Upgrades
@Tango - sounds to me like an attempt to update the MMU3 via the printer. The MMU3 has its own USB Type B connector and is updated directly. The MMU3 enablement in the printer is for the printer to recognize or not recognize the MMU (can't remember what the position needs to be for updating the printer firmware, but there's a manual for that.
I try to give answers to the best of my ability, but I am not a 3D printing pro by any means, and anything you do you do at your own risk. BTW: I have no food for…
RE: MMU3 Firmware Version: N/A - Can't Do Upgrades
@Tango - sounds to me like an attempt to update the MMU3 via the printer. The MMU3 has its own USB Type B connector and is updated directly. The MMU3 enablement in the printer is for the printer to recognize or not recognize the MMU (can't remember what the position needs to be for updating the printer firmware, but there's a manual for that.
I try to give answers to the best of my ability, but I am not a 3D printing pro by any means, and anything you do you do at your own risk. BTW: I have no food for…
RE: MMU3 Firmware Version: N/A - Can't Do Upgrades
@Tango - sounds to me like an attempt to update the MMU3 via the printer. The MMU3 has its own USB Type B connector and is updated directly. The MMU3 enablement in the printer is for the printer to recognize or not recognize the MMU (can't remember what the position needs to be for updating the printer firmware, but there's a manual for that.
I see, from the multiple replies you made, that you're having the same issues with the forum software that I'm having - it's not responding and you can't see your post is up. Looks like it's getting better now - and that responses are the normal delay for this forum.
I did see your replies this morning, the one time I was able to actually load a page. The problem is my computer is about 15' from the printer and it's kind of hard to move either of them. I'm using a USB extension cable, USB-A (male) to USB-A (female), then, at the far end, a USB-A (male) to a USB-Micro connector and plug it into the MMU.
I've now setup a folding table, disconnected the printer from everything else, except ethernet and power, and moved it to beside my computer (which barely lets me get to the keyboard) and connected it with a USB cable. I've tried multiple cables and PrusaSlicer just does not see it. (I was hoping it was a bad or cheap cable - but NO cables work!)
RE: MMU3 Firmware Version: N/A - Can't Do Upgrades
The forum problem is still persisting here in Germany; I am only by chance able to log in.
You are correct, the MMU3 has a micro USB port. However it seems like it does not like all cables nor is it recognized easily. I would first check the USB extension cable and then the micro USB cable. There are afaik cables out there which are only wired for power supply but not for data, too. Then, as far as I understand it is necessary to update the printer first and then, in a second step, the MMU3. I cannot check it currently as I am in the midst of rebuilding my MMU3 from use with MK3S+ to Core One+.
Anyway, see the comments below the update manual here: https://help.prusa3d.com/article/how-to-update-firmware-mmu3_701584
Seems like there is a certain time window as to when the MMU3 is recognized.
I'll send this note once only, hoping it is now displayed in the forum some hours after....
Cheers
Chris
I try to give answers to the best of my ability, but I am not a 3D printing pro by any means, and anything you do you do at your own risk. BTW: I have no food for…
RE: MMU3 Firmware Version: N/A - Can't Do Upgrades
Solved! Since this forum is barely useable today, I asked about it in Reddit and someone there tipped me off about the timing issues - about how PrusaSlicer can only see the MMU3 during the boot process. That led to me getting it to work. I included details when I added a new section to the front of my post on Reddit:
https://www.reddit.com/r/prusa3d/comments/1s6e30x/cant_update_mmu3/
RE: MMU3 Firmware Version: N/A - Can't Do Upgrades
I sent that previous post just in case I got lucky and it went through, and in case I couldn't post anymore.
That note on there about timing is mine - after my experience here and the help I got in the link on Reddit.