RE: Core One crash/restart
I have bonded and grounded EVERYTHING and had one crash after. I installed a Transient Voltage Spike diode (33v) across the 24v input to the board from the power supply and so far so good. No crashes yet.
RE:
I would like to investigate a little more deeply into this issue: I too experienced the crash / restart issue and indeed cured it by grounding the x/y motors. We can assume from this that the problem is electrical in nature. That much is clear. What is not clear is whether people are having this problem with pre-assembled or kit printers. If the issue is with both variants then it lies clearly lies with Prusa to investigate and rectify. If however the issue is with kit assemblies then that is a different scenario which is not entirely within the control of Prusa - Assuming that it is a problem with kits (purely for the sake of continuing these thoughts) then we should look at what each of us have done differently. I religiously followed the assembly instructions except for one tiny detail. In my case I did not align the axis belt pulleys correctly and as a result one on the belts, unbeknownst to me, was rubbing on the frame. That is a recipe for the generation of static and the subsequent electrical spikes which we assume are the cause of the crash / restart. It sounds very logical to me but what I cannot be sure of is whether the belt rubbing really was the founding cause of the issue. If you simply state that you have had this issue and that you cured it by doing 'xyz'; then it doesn't particularly add to our collective knowledge and the resolution of the actual cause.
RE: Core One crash/restart
What is not clear is whether people are having this problem with pre-assembled or kit printers.
If you read back through this long thread, you will find that the issue has been reported for both, kits and factory-assembled printers.
RE:
Thanks for this thread!
For my Prusa Core One, all I had to do was unscrew one screw from the X motor and the Y motor, then sand the surface down to the bare metal. After that, I tightened the screw back on securely. I also used a lock washer. To do this, I just had to remove the lower left side panel.
Good luck! It was a really nasty problem!
Just had another crash
Just swapping the nozzle for a different size and got a crash/restart followed by an error.
RE: Core One crash/restart
It seems that when you replaced the nozzle, you managed to grab the wires leading to the thermistor or the heating element. Check carefully whether they are in order and whether the connectors are connected correctly. If you have torn off the wires, order a new thermistor or heating element, because you can't fix this at home.
RE: Core One crash/restart
I was supporting the block with pliers. The wires had slack and everything looked fine. I started loosening the tip with a socket and super mini ratchet. When I was about halfway out it crashed. I finished changing the nozzle and it worked fine all day. Oddly, the next thing on the list of things to bond/ground is the extruder block. I wonder if me kneeling on the carpet loosening that thing caused yet another spike? If it did, that would seem to indicate that my TVS Diode did not do it's job.
RE: Core One crash/restart
I was supporting the block with pliers. The wires had slack and everything looked fine. I started loosening the tip with a socket and super mini ratchet. When I was about halfway out it crashed. I finished changing the nozzle and it worked fine all day. Oddly, the next thing on the list of things to bond/ground is the extruder block. I wonder if me kneeling on the carpet loosening that thing caused yet another spike? If it did, that would seem to indicate that my TVS Diode did not do it's job.
From changing nozzles frequently I've in the past stressed the thermistor wiring and caused it to fail. That's why I keep spares around.
RE: Core One crash/restart
+1 for reboot due to static discharge on pre-built Core One L. In both cases, I touched the corner of the case near the buddy camera.
RE:
Just to contribute to whoever is dealing with the stepper motor static issue in April 2026 - if you are doing the scrape-off-the-powder-coat method, you want to make sure you really expose the metal before putting the screws back on. I stupidly tried blindly scraping it with a scalpel and it did not work. If you have a Dremel as another user kindly suggested, definitely go straight for that. Photos attached, taken from below.
(I just did it on mine and it seems to have worked.)
RE: Core One crash/restart
I just had my first restart of this type; I opted to try star washers first. Using my multimeter to verify continuity before and after, I noticed that doing the "rear" (away from door) screw on the back left didn't fully fix ground, but the one forward of that did, maybe because it's able to also make contact with the metal rod support next to it. Or maybe it's just luck whether the star wash penetrates enough. No new crash yet but haven't printed much since.
At first I wondered why the exposed threads of the hole in the gantry wouldn't be providing ground, but I realized the bolt isn't threaded all the way down, so the bolt is hovering in between the threads not making contact. I wonder if this is how the oversight here was caused in the first place, as their CAD might assume there's contact via those threads. Clearly they grounded the gantry for this purpose. I'm surprised there's yet to be an official recognition here, but I can understand taking time, as forums can often go down wild rabbit holes on what turns out to be the wrong solution, though this seems pretty clear cut.
RE: Core One crash/restart
At first I wondered why the exposed threads of the hole in the gantry wouldn't be providing ground, but I realized the bolt isn't threaded all the way down, so the bolt is hovering in between the threads not making contact. I wonder if this is how the oversight here was caused in the first place, as their CAD might assume there's contact via those threads. Clearly they grounded the gantry for this purpose. I'm surprised there's yet to be an official recognition here, but I can understand taking time, as forums can often go down wild rabbit holes on what turns out to be the wrong solution, though this seems pretty clear cut.
The bolts must be threaded into the motor, but passing through a clearance hole in the CoreXY frame. There can't be threads in the CoreXY frame too. Otherwise it would not be a proper mechanical connection.
RE: Core One crash/restart
This solved my problem. Thanks!
But I recommend to use one of the rear motor screws to make the connection to the motor so that the cable lug does not get in the way of the extruder.
Thanks a lot to all who where involved in fixing that problem.
I ran into that issue after 6 weeks using my printer without any problems.
It was the first time I printed a plate of 190x190 mm.
The printer rebooted several times printing the first layer leaving nice blobs.I did not want to pollute my printer by milling the powder coating, so I went to a different solution which works fine.
I added two short cables to connect the motors to a definitely grounded screw.
The whole process took three hours, two hours for research and reading and one hour for fixing the problem.I have printed four of the plates mentioned above without any problem.
Thanks a lot again!Cheers
Ralf
RE: Core One crash/restart
Hello, I've been following this thread since I got my Core One. I have the same issue. Mine sounds most similar to darkmattermaker where it reboots primarily during long engagements of the x axis motor. If I let it sit there and reboot enough times, it will eventually throw a puppy error where it can't communicate with the xbuddy extension board.
I also have my printer hooked up to a UPS for troubleshooting - mine measures power draw. I didn't think it was PSU related because it's not rebooting when it draws the most power (when it's heating up the bed and element). I checked all of the cable connections I could get to easily and all of that seems to be fine.
After being able to trigger 2 reboots by simply touching the X axis motor while printing, I got to thinking that this may be a grounding issue. The chassis is powdercoated it looks like, and there are specific spots masked off to allow contact.
Using a multimeter, I looked for continuity between the X motor and the chassis ground. On my unit, there is no continuity measured from the bright screws at the top of the motor to the chassis on the X motor - but there is continuity from the same spot on the Y motor.
I hooked up a jumper between one of the X motor screws and the exposed chassis ground right below where the X motor is mounted on the left side of the unit. I have my left panel removed to make troubleshooting easier - this might not be as easy to do with the panel installed. I would include a picture, but the 'Add Media' button in the editor does not appear to do anything.
I've been checking on it regularly and I don't believe the printer has rebooted since I did this yesterday morning. My theory is that a static charge is building up in the X axis motor chassis due to the belt motion, and because it isn't grounded, eventually discharges somewhere that triggers the power panic. This is my first 3D printer, so maybe this doesn't make sense, but either way it seems to have helped. The issue has been intermittent and seems to be project-dependent, so I'm hesitant to say it's fixed for certain. I'm in the middle of a long print, but there are other projects I can print when I'm done that would more reliably trigger a reboot.
I am curious whether anyone else with a multimeter can confirm whether their working or non-working Core One has continuity between the X motor top screws and chassis ground.
Andrew
Hi everyone, especially @noumenonsense.
I want to give a huge thank you for pointing out the grounding issue on the X motor.
I have a Prusa Core One+ with MMU3 (upgraded from MK4 -> MK4S -> Core One), and I was experiencing constant spontaneous reboots, "Internal Errors," and the "Puppy Error" (#31522). These issues manifested almost exclusively during large/long prints.
Initially, I suspected a bug in the new firmware 6.5.3 (Printer) and 3.0.4 (MMU3) because the issues started right after the update. I performed a full downgrade to 6.4.0 and 3.0.3, but the problem persisted.
After reading your post, I took my multimeter and checked for continuity between the motors and the chassis. Y and Z motors - Perfect continuity, X motor - Zero continuity to the chassis ground.
I followed your lead and removed one of the X motor screws, used a Dremel to sand down a bit of the powder coating inside the mounting hole to reveal the bare metal, and put the screw back in.
Verified the continuity with the multimeter (it's perfect now) and try to print the large model that previously failed every single time. The print finished perfectly without a single reboot or error!
It seems the belt motion on the X-axis builds up a static charge that eventually discharges into the electronics when the motor isn't grounded.
Thanks again for the help!