cant flash mmu 3.0.4 firmware to MMU - Hardware, firmware and software help

RE: cant flash mmu 3.0.4 firmware to MMU

Volker — Fri, 03 Apr 2026 07:48:25 +0000

I talked with the support. First they couldn't help because they did not understand the error-log. They forwarded to an MMU expert and this "expert" replied that I need to replace the MMU. But the MMU is working fine without any problem. And the update process did find the boot loader on the MMU. I deleted all Prusa Apps and driver and reinstalled it - no success.Finally I used the computer of my wife, also a Win11 system. And surprise: the update process did work.Conclusion:- the prusa support has no clue

- the parameter of the communication on the MMU are not set for a reliable flash process. Prusa needs to fix this problem.

RE: cant flash mmu 3.0.4 firmware to MMU

Volker — Mon, 30 Mar 2026 18:58:45 +0000

I have the same problem. I checked with different cables - no difference. Once the flash process is started the MMU is reseting - therefore there is some data communication. But then nothing works. Please finde my error log.

68280797-prusa-mmu3-error-logtxt.txt

RE: cant flash mmu 3.0.4 firmware to MMU

Lynn — Fri, 27 Mar 2026 18:38:33 +0000

Yep that's how I got it done also once I found out the USB cable I was using didn't have data lines connect. They need to find some why of marking those. One of the best purchases I've made in the past year was a cable tester.

Thanks for the reply.

Tanks

RE: cant flash mmu 3.0.4 firmware to MMU

bbosveld — Fri, 27 Mar 2026 17:02:18 +0000

I have same issue as reported at top of thread.

Trying to update the firmware on my MMU3 attached to my CoreOne+. I am using MacBook Pro with Tahoe 26.2I am using the USB cable supplied with the MMU3 and the Apple dongle to connect it to my MacBook Pro (which has only USB-C ports).

Here is the output from the debug log:

avrdude-slic3r -v -p atmega2560 -c wiring -P /dev/cu.usbmodem114201 -b 115200 -D -U

flash:w:0:/Users/bbosveld/Downloads/prusa3d_fw_MMU3_3_0_4_CORE_One_CORE_One+_6_5_3(2).zip:i

avrdude-slic3r: Version 6.3-20160220-prusa3d, compiled on Nov 6 2025 at 10:29:53
Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
Copyright (c) 2007-2014 Joerg Wunsch

Using Port : /dev/cu.usbmodem114201
Using Programmer : wiring
Overriding Baud Rate : 115200
avrdude-slic3r: stk500v2_recv(): timeout
avrdude-slic3r: stk500v2_getsync(): timeout communicating with programmer
avrdude-slic3r: Could not open port: /dev/cu.usbmodem114201avrdude-slic3r done.

Thank you.

There are three choices for serial port to choose from. None of them complete successfully.

Any suggestions would be greatly appreciated.

RE: cant flash mmu 3.0.4 firmware to MMU

Mike B — Fri, 27 Mar 2026 04:59:59 +0000

I did it by using PrusaSlicer on a computer connected via USB to the MMU3 directly.

cant flash mmu 3.0.4 firmware to MMU

Lynn — Fri, 27 Mar 2026 01:50:47 +0000

I flashed the core one firmware to 6.5.3 and tried to flash the MMU to 3.0.4. If fails the update. I've tried every method to push the firmware that I could find and have had no luck.

Is there a preferred method anyone can recommend? Do I have to down flash the core one to make it work?