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Firmware updates - first of many stupid questions.  

New Member
Firmware updates - first of many stupid questions.

avrdude-slic3r -v -p atmega2560 -c wiring -P /dev/cu.usbmodem621 -b 115200 -D -U flash:w:0:/Users/timjennings/Downloads/prusa3d_fw_3_10_0_MK3S (1)/prusa3d_fw_MK3S_3_10_0_4481.hex:i

avrdude-slic3r: Version 6.3-20160220-prusa3d, compiled on Jul 16 2021 at 12:34:41 Copyright (c) 2000-2005 Brian Dean, Copyright (c) 2007-2014 Joerg Wunsch

Using Port : /dev/cu.usbmodem621 Using Programmer : wiring Overriding Baud Rate : 115200avrdude-slic3r: stk500v2_recv(): timeoutavrdude-slic3r: stk500v2_getsync(): timeout communicating with programmeravrdude-slic3r: Could not open port: /dev/cu.usbmodem621

avrdude-slic3r done. Thank you.

Greetings. I just got my first printer as a gift/hand me down from my brother.

I am having the two lines of squares on the LCD issue, which seems common(?) and in trying to fix it I am trying to flash the firmware but get the above message... I have the appropriate software on my older Mac. 

As with all communities, there are many solutions offered but if someone could point me in the direction of the best solution I'd appreciate it!

Many thanks!!

Posted : 10/11/2021 2:47 pm
Dan Rogers
Noble Member
Look up factory reset

If you can't open the port you can't flash it.  Time for that ole factory reset.

Posted : 11/11/2021 8:57 am
New Member
Topic starter answered:
RE: Firmware updates - first of many stupid questions.

Many thanks Dan - Sadly that didn't seem to work either. Let me recap:

  • Turning the printer on only seems to light up the display, there are no other noises or signs of movement.
  • resetting by clicking the X button and jog wheel has no discernable result
  • trying to flash the firmware gives the above "Could not open port: /dev/cu.usbmodem621" error
  • I have checked the ribbon wiring from the electronics box to the display, they appear to be firmly connected at both ends. However, I understand "flatness" is a common area for concern? these were a little long and twisted.


  • are the less than "flat" ribbon cables a real area of concern - if so what do i go hunting for?
  • is there an effective method for bug hunting in the Mk3?

Many thanks again.

Posted : 15/11/2021 11:47 am
Illustrious Member
RE: Firmware updates - first of many stupid questions.

It almost sounds like the board doesn’t have a boot loader on it. These boards should have a boot loader installed at the factory, before even Prusa get them, when they are manufactured. Without a boot loader they are just inert and you can’t even flash them. 
This needs taking up with Prusa. 

Posted : 15/11/2021 4:32 pm