6.4.1 Stable firmware for Prusa XL
Summary
- Improved phase stepping calibration
- Fixed homing issues with no tool picked
- Fixed toolchanger service moves being affected by user feedrate override
- Relaxed nozzle cleaning checks to prevent false nozzle cleaning failed errors
- Relaxed print fan selftest thresholds to reduce false failures
- Known issue - Power panic resulting in a BSOD
This is the stable release of firmware 6.4.1 for the Prusa XL bringing targeted stability improvements and fixes - most notably addressing several homing and toolchanging reliability issues.
Improved phase stepping calibration
The switch to the new universal phase stepping calibration in the 6.4 release caused a regression in the calibration quality for some XL users. In 6.4.1, the calibration method has been refined and further improved by backporting phase stepping fixes from the 6.5 releases. These changes enhance overall calibration reliability and address regressions introduced in earlier 6.4 builds.
Fixed homing issues with no tool picked
Homing without a tool picked could cause audible motor skipping or put the printer into an invalid state under certain conditions. The fix ensures that the axes are properly homed before attempting a tool pick, preventing both issues.
Fixed toolchanger service moves being affected by user feedrate
Tool parking, picking, and alignment moves could be slowed down if a low feedrate was set in G-code beforehand. This could lead to unreliable tool changes. All toolchanger service moves now run at their intended speeds regardless of the user feedrate setting.
Relaxed print fan selftest thresholds to reduce false failures
The print fan selftest could incorrectly report a failure on some units due to tight RPM thresholds that did not account for normal fan-to-fan variation across different fan shroud revisions. The thresholds have been relaxed to reduce false failures.
Release notes:
https://github.com/prusa3d/Prusa-Firmware-Buddy/releases/tag/v6.4.1
RE: 6.4.1 Stable firmware for Prusa XL
Are there any changes in 6.4.1 final versus 6.4.1-RC? The RC had some nasty issues (eg, https://github.com/prusa3d/Prusa-Firmware-Buddy/issues/5236). Having seen this issue and others in 6.4.1-RC and other recent XL firmwares, I have very low confidence that 6.4.1 final is safe to use. I'm planning to stick with 6.2.6 for the time being.
RE:
It’s hard to evaluate the developers’ work—how they test or what steps they take to reproduce the bugs.
The fact is that the current firmware versions for the XL and for the Gen C1 and C1L are far from optimal.
That’s why I won’t start testing anything until the number of GitHub commits decreases or the reports here about new bugs in the latest firmware releases become less frequent
For now, the Prusa XL with 6.2.6 and the C1 with 6.3.4 are my stable candidates for working with.
Mods for Core One: Core One HT 450 degrees, Comfortable display , Very fast print start and Reducing noises
Mods for Prusa XL: Very fast print start
RE: 6.4.1 Stable firmware for Prusa XL
"Relaxed print fan selftest thresholds to reduce false failures"
So after installing the firmware, the control panel told me to re-run calibrations. Guess what, fans 1-4 failed 5 passed. It interesting to note that I never had a fan failure prior to firmware update. Ill take any suggestions since now my control panel is giving me warnings every time I try to print, and yes the prints are fine and so are the fans. Any chance we can get a setting to tell it to ignore the fan test if we're certain they are working correctly until a final fix is published? Super annoying!
RE: 6.4.1 Stable firmware for Prusa XL
Please create a ticket here.
https://github.com/prusa3d/Prusa-Firmware-Buddy/issues
While there might be a solution here in the forum, it’s more straightforward on GitHub.
Mods for Core One: Core One HT 450 degrees, Comfortable display , Very fast print start and Reducing noises
Mods for Prusa XL: Very fast print start
RE: 6.4.1 Stable firmware for Prusa XL
The fan shrouds are to restrictive and don't allow the fan up to speed. If you take them all off and re-do the calibration, they should pass. Lots of prints for up graded shrouds that cool the part more evenly. Not sure if they flow better.
RE: 6.4.1 Stable firmware for Prusa XL
Not only the well known print fan bug persists, but we now also have new bug ! Hotend fans also fail during calibration. I've completely taken apart the fans, the print fans passes but the hotend fans fail every single time.
RE: 6.4.1 Stable firmware for Prusa XL
I just went back to the old firmware.
RE: 6.4.1 Stable firmware for Prusa XL
I reverted back to 6.4.1RC. Did not work. Reverted to 6.2.6. Did not work. Performed a hard reset and flashed 6.2.6 again. Did not work.
RE: 6.4.1 Stable firmware for Prusa XL
Disassembled the fans, cleaned everything with contact cleaner, did not work. Ordered new fans
RE: 6.4.1 Stable firmware for Prusa XL
Just throwing ideas at you. Can you take the fan off and let it hang still wired up? See if it gets enough rpms to pass? Also on the part fan it had an option for a black fan or silver. Does that fan have 2 options?
RE: 6.4.1 Stable firmware for Prusa XL
I already did that. I have 2 black 3 silver fans. Blacks always pass. Silvers will pass if shroud is removed. This issue is something entirely different though, no mateer what I do, hotend fans, not print fans are failing on the newer toolheads. Old ones are fine.
RE: 6.4.1 Stable firmware for Prusa XL
Well that just sucks. Good luck...
RE: 6.4.1 Stable firmware for Prusa XL
I've managed to pass the test. It took us 1.5 hours to find the exact pressure to apply to each fan with our fingers during the test. This is the Prusa experience in 2026 !
RE: 6.4.1 Stable firmware for Prusa XL
Evolution through revolution. Revolution through evolution! A toast to progress!
Mods for Core One: Core One HT 450 degrees, Comfortable display , Very fast print start and Reducing noises
Mods for Prusa XL: Very fast print start
RE: 6.4.1 Stable firmware for Prusa XL
Get a solid beep at start of print, after pressing print button. It can last as long as initial tool head checks. Then stops and continues printing.
RE: 6.4.1 Stable firmware for Prusa XL
Hello, Well, given the bugs I'm still encountering, I'm sticking with version 6.2.6. I don't understand Prusa anymore! Releasing a firmware with all these bugs is unacceptable.
MK3S+, XL 5 tools
RE: 6.4.1 Stable firmware for Prusa XL
FYI: The beep was being genated by a 450VA UPS surge protection over load and had nothing to do with the printer. This new firmware must draw more power for the initial start. I replaced iy with a larger UPS and the beep is now gone 🙂 .sorry..
RE: 6.4.1 Stable firmware for Prusa XL
Unfortunately, I’m not familiar with Prusa’s internal processes. That’s why I can’t say whether Prusa has selected testers who own a Prusa XL and test the firmware BEFORE it’s released.
I stand by my opinion that I won’t switch from firmware 6.2.6 as long as the issues with the 6.4.x versions don’t improve.
Mods for Core One: Core One HT 450 degrees, Comfortable display , Very fast print start and Reducing noises
Mods for Prusa XL: Very fast print start
RE: 6.4.1 Stable firmware for Prusa XL
Does anyone NOT have any issues after upgrading?