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Firmware 3.5.2-RC1 for Original Prusa i3 MK2.5  

Jakub Dolezal
Firmware 3.5.2-RC1 for Original Prusa i3 MK2.5

UPDATE: Final version is out

Hi guys,
this is an upgrade of the firmware for the Original Prusa i3 MK2.5. Keep in mind this a release candidate (testing version) for experienced users 😎

What is new?
-> More quiet print fan operation
-> Heatbed regulation improved
-> Improved heater temperature regulation
-> Spool join for multi-material prints
-> Smarter load/unload function
-> Mintemp for MK2.5 updated
-> SD card menu is shown automatically when the card is inserted
-> Safer communication between MMU2 and printer
-> Crash detection for zero target temperature fixed

More quiet print fan operation:
This change is significant especially for low fan speeds.

Heatbed regulation improved:
Heatbed PWM now works on a higher frequency. This helps to reduce the power supplies "clicking" noises.

Improved heater temperature regulation:
When changing temperatures during the print, temperature regulation was very slow in some cases led to preheat error. Regulation has been improved. This should solve issue #1362.

SpoolJoin for multi-material prints:
It is now possible to use the "SpoolJoin" function also with multi-material prints. If some filament is depleted, the printer replaces it with next filament for the rest of print (for example if filament 2 was depleted, the printer starts using filament 3 instead). If there is no filament which can be used (all filaments were depleted), the printer waits for the user to insert new filament manually.

Smarter load/unload function:
If a user chooses load (or unload) in the menu with a cold nozzle, nozzle preheat menu automatically appears. After selecting material, preheat starts. When the nozzle is hot and the printer is ready for a load, beeper signal occurs. This function is working on single material printers with load/autoload and unload. It is not currently implemented for multi-material printers (load to nozzle, unload and eject).

Mintemp for MK2.5 updated:
"Mintemp" is now checked after a short period of preheating. This is necessary for maximum reliability on all MK2.5 Rambo boards.

Supported printers:
Original Prusa i3 MK3
Original Prusa i3 MK3 MMU2
Original Prusa i3 MK2.5
Original Prusa i3 MK2.5 MMU2

Download link:

Firmware flashing guide:

Please report any bug here:

As always, we wish you happy printing and look forward to your feedback!

Assembly manuals / Knowledge Base
The guy behind Prusa assembly manuals......
Posted : 08/02/2019 11:49 am
New Member
Re: Firmware 3.5.2-RC1 for Original Prusa i3 MK2.5

I upgraded to FIRMWARE 3.5.2 - from Feb 12 (there seems to be no thread for that version specificalyl yet).

Anyhow, I am now getting
"Some problem encountered Z leveling enforced" while starting a job. This happens with one of the three back row points (Z:3 / Z2 / Z:1). I then do the Z leveling, it starts over again and sometimes it succeeds in second go, but like just now I had this 3 times in a row with different back row points.

My cal data shows
Y distance L:7.71mm / R:7.73mm
skew 0.06
x: -1.83
y: -0.79
if that helps perhaps.

Have some thresholds changed or what should I be looking for to solve this. I have done the whole XYZ calibaration reset / recalibrate a few times and that process succeeds with no errors.

Posted : 17/02/2019 10:43 am