Banding on Y face only

Bambu Lab A1 Series Bambu Lab A1 mini
1

Hi, I have been trying to get my new A1 mini to work properly, but I keep getting very noticeable bands on the Y axis face only. Other faces are fine.

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I have run multiple calibrations to no avail. Searching around, I found some discussion on the Y belt being possibly loose, or on some screws being loose.
I tightened all the screw on and under the plate, rerun the self-calibration, but no effect.

Then I tried to follow the official maintenance documentation (A1 mini Maintenance Guidelines | Bambu Lab Wiki) to see if the belt was loose, but I can’t figure out what I’m supposed to do.
I opened the rear panel, loosened the bottom screw as the instructions say, but then they say to push on the block? Nothing moved at all in any direction. I undid the bottom screw completely and tried again, but it’s all solid and nothing moves. Still, I retightened the screw and calibrated again, but no change.

Any advice? I can’t tell if I’m missing some obvious thing to do.
Also, I guess the problem could be elsewhere, but the fact I only get this print defects on the faces corresponding to the Y axis movement seem to suggest it has something to do with it.

2

Hi,
I’m betting on poor X belt tension…

3

I’ll try that too
Are the instructions on the wiki accurate? Meaning, just loosen the screw, move the toolhead back and forth a few times and tighten the screw again?
I’m confused how that would achieve tightening the belt

4

Don’t forget the Vibration Compensation, then have a try to see if print is better.

5

I tried the x axis tighening, which again, feels very strange (instructions say to loosen the screw, then just move the piece back and forth a few times, then retighten the screw). I don’t get how that would supposedly tighten the belt, but I did it anyway.
Run the full calibration later.

No changes at all. Still plenty of horizontal lines. I’ve now tried customer support too and I’m waiting for an answer