6.5.3 firmware seems really broken
I have two MK4S printers. Both are on 6.4.0. Both, sadly, have been 100% idle for about three weeks since I have been attending to other matters. I haven't interacted with them at all.
This morning, both printers started sending me "printer needs attention" messages through iOS at completely random intervals - sometimes a few hours in between, sometimes a few minutes. But neither printer indicated the nature of the "needs attention" error. At most, Prusa Connect showed the occurrence of fleeting "needs attention" statuses on both printers and suggested: "Check the display of your printer for more info." But both printers were just sitting there idle with no information, or even any indication that they "needed attention" for any reason.
Eventually, I thought I'd search to see if a new firmware was available - yep, 6.5.3, just released a couple of days ago. That has to be the reason, although the current firmware *and* Prusa Connect certainly weren't helping me figure that out!
So I visited Prusa Connect and clicked the "download new firmware" button on both printers. Both downloaded it into their queue and then... did... nothing? They didn't flash and they just discarded it.
I downloaded the 6.5.3 firmware and manually transferred it to both printers. One printer stored it; the other just silently dropped it.
I clicked "Flash" on the printer that accepted it. That printer said it was starting to flash the update, and then... just... didn't. The file is gone and it's still reporting 6.4.0.
This experience reminds me of all the time that I spent in the 1990's manually downloading and installing printer drivers. I don't have a lot of nostalgia for those busywork tasks, and I don't appreciate that Prusa is making me go through this process.
The kicker is that the firmware doesn't have even a single improvement for the MK4S line. It's all CL1 and INDX stuff. Further reinforcing my belief that the MK4 line is well and truly dead to Prusa.
This is all a sad state of affairs and it moves me just a little bit closer to "upgrading" from these not-completely-dead-yet MK4S printers to... my first Bambu Lab printer.
RE: 6.5.3 firmware seems really broken
My upgrade experience through Prusa Connect (for my MK4S) was also quite weird. I initiated the upgrade from work, but Prusa Connect never seemed to reflect the completion of the upgrade. When I got home I tried again and same result. But the printer did reset and did show the 6.5.3 version so the upgrade was working - it's Connect<>MK4S that is not reliable.
I also spent lots of $ and time to add the enclosure to my MK4S (and MMU3), and I was seriously going to upgrade to Core 1. But I think 75% of the existing machine would be discarded. So, I am thinking about buying the Core 1 kit instead and either continuing with 2 printers or selling the MK4S. It's still a great printer... and they won't stop selling parts for it for a long long time!
Prusa MK4 since Jan 2024, MK4S/MMU3 since Jan 2025, Printables: @MikeB_1505898
RE:
It's still a great printer... and they won't stop selling parts for it for a long long time!
It was a great printer in 2024. But 3D printer technology has steadily moved forward. The quality of prints that roll off of the latest Bambu Lab printers consistently exceeds that of the MK4S. Bambu Lab printers have great features like built-in cameras and integrated multi-material solutions, as opposed the MMU which is exceptionally janky by comparison. That gap is guaranteed to grow over time and Prusa hasn't uttered a peep about the MK4 line in two years.
It seems extremely clear that the MK4 line will not be getting any more hardware upgrades and will retain its status as the best printer of 2024.
RE: 6.5.3 firmware seems really broken
Hm, my experience so far with 6.5.3 is that an apparent filament handling bug introduced by 6.4.0 has been fixed. The 6.4.0 firmware never saw that filament was already loaded when the printer was first turned on. I'd always have to unload the already loaded filament and load it again before continuing. I attributed the error the 6.4.0's 'filament retraction' feature. This was never a problem before 6.4.0, and appears to be fixed by 6.5.3.
RE: 6.5.3 firmware seems really broken
OK, so the MK4S is one of the great bedslingers then. That's still true. Your hardware upgrade path from here is the Core 1, which will make it one of the best printers of 2026, especially once INDX is available. Bambu doesn't supply an upgrade path from Mendel to Core XY - in fact, does anybody else?
BTW, these are the changes in 6.5.3 that apply to the MK4S. It's disingenuous to say they've dropped the MK4S like a hot potato.
New features and improvements
- Massively speed up MMU filament changes [MMU]
- Preload all MMU slots at once [MMU]
Fixes
- Fixed layer shifts during high-speed curved moves M1704
- MMU load test gcode now considers toolmapping [MMU]
- Fixed MMU sending spurious attention reports to Prusa Connect during normal toolchanges [MMU]
- Fixed crash/BSOD on M501 (restore settings) (#4912)
- Fixed gearbox alignment test showing wrong status when skipped
Call me a fanboy, but.... well, maybe I am! I bought the printer in the first place (my first and only printer BTW) because of Prusa's reputation for quality, support, high standards, and openness. I'm convinced that openness is why so many people get frustrated with them, because they hear about the next new thing and expect it on their doorstep in a week. But Prusa talks while they're developing, not when the user manual is done. And I've been extremely happy with it. But like any technology (ask me about my Macintosh journey since 1994) there will be jumps in technology that cost you more, and some that are less expensive/drastic.
I'm confused why people are expecting effort to continue on the MK4S when there's a clear upgrade path to a MUCH better technology. I expect the Slicer and firmware to continue to be supported, but please don't spend much more than 0.5 HW dev (maybe train interns) on new hardware for the MK4S!
And BTW, where will 3D printing get their advances if Prusa is gone? You think Bambu will sink tons of R&D into leaps of performance? They're much more likely to chase profits than progress...
I don't know why I'm rambling - feel free to disagree, I always listen, but I might not change my mind...
Prusa MK4 since Jan 2024, MK4S/MMU3 since Jan 2025, Printables: @MikeB_1505898
The quality of prints that roll off of the latest Bambu Lab printers consistently exceeds that of the MK4S.
Not really, it's a mixture of advertising hype and genuine reductions in the amount of maintenance required to preserve quality. In practice there has not been a noticeable increase in print quality from a properly tuned Mk2 to any current FDM printer with the same filaments. The Mk2 generation exceeded the precision required to extrude within the possible accuracy of the common (and practical) nozzle diameters and no advances can improve on that. OK, speed, overhang performance, a greater range of printable materials and many other peripheral improvements have accrued but basic print quality, no.
That said: after being left unattended for a while bedslingers and other open architecture printers usually need surface cleaning - dusting and cobweb removal - especially the smooth rods, followed by lubrication.
Cheerio,
RE: 6.5.3 firmware seems really broken
Just updated to 6.5.3: It also updated the loader to 2.60. When the bed traverses from the front to back (y-axis), it hesitates. Kind of like a hard hiccup or a stutter. Reverted back to 6.4.0 and the problem disappeared. However the loader didn't revert back. Also getting a message from Prusa Connect that the printer needs attention. Before the update, I was happy with what I had. I should have left well enough alone.
RE: 6.5.3 firmware seems really broken
Just updated to 6.5.3: It also updated the loader to 2.60. When the bed traverses from the front to back (y-axis), it hesitates. Kind of like a hard hiccup or a stutter. Reverted back to 6.4.0 and the problem disappeared. However the loader didn't revert back. Also getting a message from Prusa Connect that the printer needs attention. Before the update, I was happy with what I had. I should have left well enough alone.
This I think I am seeing as well, but both on the X and Y axes. It seems to start and stop (or maybe just hesitate) a few times on a long fast travel. I hope it's not a performance issue where the controller isn't keeping up with the motion...
Prusa MK4 since Jan 2024, MK4S/MMU3 since Jan 2025, Printables: @MikeB_1505898
RE:
These two issues have been raised with the firmware:
https://github.com/prusa3d/Prusa-Firmware-Buddy/issues/5227
https://github.com/prusa3d/Prusa-Firmware-Buddy/issues/5209
Only suggestion to try so far is disabling "Avoid crossing perimeters". I haven't tried it yet.
Prusa MK4 since Jan 2024, MK4S/MMU3 since Jan 2025, Printables: @MikeB_1505898
RE: 6.5.3 firmware seems really broken
Mike B: I haven't noticed it jerking along the x-axis. But it's certainly evident along the y-axis. It's very obvious when rapid transiting full travel, front to back.