Posted by: @noumenonsense

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!

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.

Posted by: @ralgre

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

 

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. 

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.

(I just did it on mine and it seems to have worked.)

Posted by: @ron-s-2

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.