Updated to Firmware 6.5.3 (MK4S with MMU3) - MMU3 not working anymore
 
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Updated to Firmware 6.5.3 (MK4S with MMU3) - MMU3 not working anymore  

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Dave Hammer
(@dave-hammer)
Member
Updated to Firmware 6.5.3 (MK4S with MMU3) - MMU3 not working anymore

Hello guys,

I have installed the firmware:

  • MK4_MK4S_MK3.9_MK3.9S_firmware_6.5.3.bbf
  • with the MMU3_FW3.0.4+936.hex

(Downloaded in the offical PRISMA Firmware and Download section)

My Printer is an MK4S with MMU3, but after this Firmware update, my printer says, that the MMU3 is not compatible with the Firmware 6.5.3I did a hard firmware reset, problem still occures.

After that, I have installed the Firmware:

  • MK4_MK4S_MK3.9_MK3.9S_firmware_6.4.0.bbf
  • MMU3_FW3.0.3+896.hex

This works for me.

But, next day, it says: to much power onthe MMU 🙁
I did a hard reset again, with the 6.4.0.bbf and 896.hex - and works again.. maybe for more than one day.

I also checked all cables, but all seems fine.

Is there an older firmware version, I could download and use for my MK4S with MMU3?Just got lost in the GitHub Repo.

Thank you in advance!

Best regards,
David

Posted : 06/05/2026 7:21 am
Borq
 Borq
(@borq-2)
Member
RE: Updated to Firmware 6.5.3 (MK4S with MMU3) - MMU3 not working anymore

I experienced this too.

Solved by flashing this
https://github.com/prusa3d/Prusa-Firmware-MMU/releases

onto the MMU using this guide
https://help.prusa3d.com/article/how-to-update-firmware-mmu3_701584

! Beware you use a data ready micro usb (not all loading cables are!!) otherwise it wont show in the flash software

Posted : 08/05/2026 11:21 am
2 people liked
Dave Hammer
(@dave-hammer)
Member
Topic starter answered:
RE: Updated to Firmware 6.5.3 (MK4S with MMU3) - MMU3 not working anymore

Hello Borq,
thank you for your reply!

I downloaded the files. In my situation my printer stands in the cellar, and my PC is an desktop pc in the first floor, so I don't have a direct connection. I tried it with an USB stick, I saved the MMU3 firmware to the USB stick with an micro usb adapter - but I stuck on this.

Installed the newest MK4S firmware and added to the USB stick also the newest MMU3 file. Also not working.

Do you know, how I cann install the firmware with just an USB Stick? Maybe with the Adapter it is not working, why ever.

Posted : 22/05/2026 7:15 am
Dave Hammer
(@dave-hammer)
Member
Topic starter answered:
RE: Updated to Firmware 6.5.3 (MK4S with MMU3) - MMU3 not working anymore

An additional information. The error, that the MMU has to much power occures after I switch the 3d printer off, and on (with some pause in between).
This is really annoying. 🙁

Posted : 22/05/2026 11:18 am
vhubbard
(@vhubbard)
Reputable Member
RE: Updated to Firmware 6.5.3 (MK4S with MMU3) - MMU3 not working anymore

 

Posted by: @dave-hammer

Hello Borq,
thank you for your reply!

I downloaded the files. In my situation my printer stands in the cellar, and my PC is an desktop pc in the first floor, so I don't have a direct connection. I tried it with an USB stick, I saved the MMU3 firmware to the USB stick with an micro usb adapter - but I stuck on this.

Installed the newest MK4S firmware and added to the USB stick also the newest MMU3 file. Also not working.

Do you know, how I cann install the firmware with just an USB Stick? Maybe with the Adapter it is not working, why ever.

You must use the PC and USB cable connected to the MMU3 to update the MMU3.  The instructions show no other options. .   It must be pushed to the MMU3.   The MMU3 firmware cannot be pulled from the USB, the MMU3 is not cabaple of doing that. 

See if you can invite a friend over with a laptop and have an update party.   

Posted : 23/05/2026 12:56 pm
Mike B
(@mike-b-3)
Estimable Member
RE: Updated to Firmware 6.5.3 (MK4S with MMU3) - MMU3 not working anymore

Or just bring the printer up to the PC temporarily to do the update.

Prusa MK4 since Jan 2024, MK4S/MMU3 since Jan 2025, Printables: @MikeB_1505898

Posted : 25/05/2026 7:32 pm
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