Core One L AC Controller Fault - Printer Currently Unusable - Error 35338
Hey guys, I desperately need some assistance with my core one. I was on support chat last night for about two hours or longer, trying to get this error fixed. We tried downgrading the firmware and then re-upgrading the firmware but every time I turned the printer on, I got the following error. This is the Prusa Core One L. I received it in January of this year, 2026, and I've been printing only with PLA up until this week. Then I tried to print PETG for a bit stronger part and got this error.No matter what I do when I boot up the printer, it goes right into this error. Once the boot-up happens, I do get to see the normal control panel for about 1 second, and then it just shuts off and reboots. I'm in desperate need of help with this, and I've spoken with Prusa via chat, but I haven't heard back from them yet. Is there anybody who can help me with this? I need my printer back up and running, and it is a terrible feeling when you spend this much money on a high-end printer and run into a problem like this.I even read online that having a UPS unit plugged into it to get better sinewave electricity would help, so I ordered one that will be delivered on Thursday, but I still would do anything to get this back to normal printing and reliable. I need to be able to print PLA and PETG, and eventually a few other filament types, with dependability. If anyone out there can help me with this as soon as possible, I would greatly appreciate it. I've been a big fan of Prusa for quite a while, and I've had the MK3, MK4, and the regular Core one. I've sold each one of them to upgrade to the newer version and now have this terrible issue, only a few months in. Please Help Prusa!!!! My printer is currently unusable.
RE: Core One L AC Controller Fault - Printer Currently Unusable - Error 35338
http://prusa.io/35338 says it needs to be handled via help chat, if factory reset in firmware, moving some cabled does not help then you might be unlucky and your bed fried and needs to be replaced.
See my GitHub and printables.com for some 3d stuff that you may like.
RE: Core One L AC Controller Fault - Printer Currently Unusable - Error 35338
Thanks for the reply. I've been chatting back and forth with someone on the help chat and am going to send them an email this evening with all the information. If it's something that I can do myself and replace, I do have that capability. Mechanical engineer. Sending it back would be a huge pain. Rather, I would do what I can to get it up and running reliably if possible
RE:
Hello there ,
I currently have the same issue ... except I wasn't able to do one single print ...
Do you have any update ? Is your problem being solve by chat support ?
Thanks for your reply !
Cheers
RE: Core One L AC Controller Fault - Printer Currently Unusable - Error 35338
Hi,
We encounter this behaviour this week with 2 printers CoreOne L.
Facts:
- The error came exactly at the same time on both printers.
- The printers were working well after a power cycle. However, we cannot resume printing.
- The 2 CoreOne L were connected on the same UPS (Back-up UPS 650). A rather low-power output for 2 printers
- We also have 2 other printer (CoreOne) running at the same time: they were connected on a UPS et we had no problem.
AI suggest to connnect each printer into a UPS with at least 850VA. We may purchase a CyberPower CP850PFCLCD or a APC Back-UPS Pro BR850M2-LM to prevent any power glitch.
RE: Core One L AC Controller Fault - Printer Currently Unusable - Error 35338
The C1L AC controller does not work with a UPS, even 6ms, is too slow. Would be great if Prusa fixed this issue, but don't hold your breath.
Core One L MMU3, MK3S
RE: Core One L AC Controller Fault - Printer Currently Unusable - Error 35338
My literally ancient APC Smart-UPS 1000 from year 2005 passes the power loss without issues while L is printing.
The only problem is on the very beginning when the bed heats up - it literally overloads the UPS for 2min because it slurps over 1000VA during that period.
See my GitHub and printables.com for some 3d stuff that you may like.
RE: Core One L AC Controller Fault - Printer Currently Unusable - Error 35338
My APC BE750BB Back-UPS 750VA, from 2008, so likely the same series, they didn't change the model often back then. After 6.5.3, I could get some pass on power loss, but could not get a pass when the power resumed.
Core One L MMU3, MK3S
RE: Core One L AC Controller Fault - Printer Currently Unusable - Error 35338
The batteries are from 2022, and they are rated for about 7 years.
1. 19:20 start of the bed heating and nozzle heating, you can see the load shoots into the moon, drawing over the UPS capacity
2. 19:23 end of the bed heating, nozzle heats up
3. 19:27 removed power plug from the wall switch to the UPS
4. 19:28 plugged in the power cable back into the wall
5. 19:30 manually aborted print
You can see graphs preview here https://snapshots.raintank.io/dashboard/snapshot/0GhjVtVdlkU6ehuUv68dbtYY6L6FzTua
below is the image preview
See my GitHub and printables.com for some 3d stuff that you may like.
RE: Core One L AC Controller Fault - Printer Currently Unusable - Error 35338
I guess the 22oV may actually work, I am running 120V.
Core One L MMU3, MK3S
RE: Core One L AC Controller Fault - Printer Currently Unusable - Error 35338
Hi
I am still confused.
If I purchase a 1000VA UPS for my CoreOne L, does it prevent the error on screen ?
Or it create another error that prevent resuming printing later
(or both ) ??
RE: Core One L AC Controller Fault - Printer Currently Unusable - Error 35338
SbackUPS vs SmartUPS are different technologies (and price range), mine is SUA model, though.
BackUPS = standby
SmartUPS (SUA units) = line interactive
SmartUPS (SURT units) = double conversion online
At work I had some BackUPS but they were okay only for some workstations and were sometimes flaky, after that we switched to SmartUPS and problem solved.
See my GitHub and printables.com for some 3d stuff that you may like.
RE: Core One L AC Controller Fault - Printer Currently Unusable - Error 35338
Prusa worked with me on the issue, and I actually had to send the printer back. They sent me a replacement printer. They did this extremely quickly and were great about the replacement.
RE: Core One L AC Controller Fault - Printer Currently Unusable - Error 35338
Same here: I am running at 110VAC 60Hz in Canada