Mini+ kit: Z Axis fails self test  

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Eric
 Eric
(@eric-19)
Active Member

Hello!

I finished assembling my MINI+ kit (and most of the gummy bears). I saw that there was a newer firmware, so I upgraded to 4.3.1. Then I tried to run the self-test and the Z-Axis failed! I've tried several times, same result. I've double checked the wiring and everything is properly connected as far as I can tell. The Z-Axis motor does move, but it stops when traveling up during the test and fails. It doesn't fail consistently in the same location. I've seen it go up about halfway before failing, though usually it fails close to the print bed.

Here's a video: 
https://photos.app.goo.gl/bBYcY68oL17Zbugk7

The Selftest MINI article doesn't contain any specifics about what might cause the Z Axis to fail, or what to do to fix it.
https://help.prusa3d.com/en/article/selftest-mini_112055

Any suggestions would be greatly appreciated, thank you!

Best Answer by Eric:

Update: I checked the resistance of the wires for the heatbead and thermistor, both are fine. I also started to loosen the screws to remove the Z-Axis and in the process, moved it up by hand and noticed that it was much easier. The two screws that hold on the threaded piece to the Z-Axis carriage were just a little too tight, which must have flexed that nut and caused some resistance.

All selftest checks now pass!

Posted : 27/02/2021 7:39 am
Turro75
(@turro75)
Estimable Member

Axis test fails if the path is long/short that expected (not your case) or if the motor gets too much resistance on movement. 

I would try loosening the z frame screws and check again.

anyway ask to prusa support, it could be the z frame tilted that constraints the leadscrew or (hopefully not) something wrong in the motor/driver.

Posted : 27/02/2021 12:38 pm
Eric
 Eric
(@eric-19)
Active Member

Ah, resistance on the axis could be the problem. I'll check the screws and also measure for tilt on the axis rods to see if they are slightly skewed and causing more resistance than expected. Thanks for the tip!

Posted : 27/02/2021 5:48 pm
Eric
 Eric
(@eric-19)
Active Member

For my own information, is there developer documentation somewhere about how things like the self test functions are designed to work? I looked through some of the code on GitHub, but didn't really get a sense of the intent.

Posted : 27/02/2021 5:54 pm
Turro75
(@turro75)
Estimable Member

the best option You have (other than ask prusa guys) is to use 4.3.0 rc1 as that release write down a txt file in the usb stick at the end of the last test so You can better check the failure reason.

the file creation has been removed on newer firmware as it often happened mess with the usb stick that forced reformatting.

Posted : 27/02/2021 6:16 pm
karl-herbert
(@karl-herbert)
Illustrious Member

@eric-19

Can you move the Z-axis up and down manually without errors?

Maybe the self test works with a FW downgrade to 4.2.0. I would just test it.

Maybe you should report this to Prusa! Just log in with your Prusa account and select the eshop. After a few seconds the chat window should appear on the lower right corner. If the chat window does not open, disable a possibly activated adblocker or try another browser.

good luck!

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen....
Posted : 27/02/2021 6:33 pm
Eric
 Eric
(@eric-19)
Active Member

Downgrading the firmware sounds like a good first step, especially if it writes some debug information to the USB drive. I'll give 4.2.0 try now then 4.3.0-RC1. Thanks for the suggestions!

Posted : 27/02/2021 6:57 pm
Eric
 Eric
(@eric-19)
Active Member

One step forward, two steps back.

I downgraded to 4.2.1 which failed the selftest immediately with a MINTEMP error. I used the manual Z-axis control to move it up and may have discovered one problem. It stalled out about halfway (~68 steps) so I moved it backed down and noticed gunk on the threads. I cleaned the threads off with a towel & IPA which allowed it to move up and down more freely. However, I went back to 4.3.1 and the Z-axis still fails the selftest. Maybe I need to disassemble that axis and clean the threads and adapter very well, or just apply some grease?

But, the wizard on 4.3.1 also failed with an error about the heatbed thermistor wire being possibly damaged? (Error code 12207)

Here's what's weird: when I ran the selftest, it did not raise any errors during the heatbed test. Strange, right?

Posted : 27/02/2021 7:39 pm
Eric
 Eric
(@eric-19)
Active Member

Update: I checked the resistance of the wires for the heatbead and thermistor, both are fine. I also started to loosen the screws to remove the Z-Axis and in the process, moved it up by hand and noticed that it was much easier. The two screws that hold on the threaded piece to the Z-Axis carriage were just a little too tight, which must have flexed that nut and caused some resistance.

All selftest checks now pass!

Posted : 28/02/2021 5:28 am
mwv liked
Turro75
(@turro75)
Estimable Member

Good to hear that!

The self assembly is often painful but allows You to learn a lot of stuff. Well done.

Posted : 28/02/2021 9:30 am
Eric liked
mwv
 mwv
(@mwv)
New Member

Thank you!  I had the same problem and loosening the screws that hold the threaded piece to the extruder/x-axis motor carriage was exactly the solution.  Thanks so much!

Posted : 11/03/2021 1:25 pm
Eric liked
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