Over the past month or so many of my 3D print jobs failed due to what appeared to be nozzle collisions. This was especially true when there was a significant disparity in the height of objects being printed on the same build plate. I adjusted all the slicing parameters suggested by multiple sources on the internet and achieved some success but the performance never returned to that obtained when the Bambu A1 was brand new. The problems started after 1000 hours of use, the vast majority with PLA filament. All the screws in the extruder and nozzle (0.4 mm) assembly proved to be snug and calibration proceeded without any problems. The X, Y and Z lubrication areas were cleaned and fresh lubricant applied. There was one interesting finding where filament poop managed to find its way into the Z-axis gear.assembly. Initially I thought that this was the answer to the nozzle collision problem, however after removal of this debris and carefully cleaning each side the problem persisted. There was also an issue with increasingly frequent failures to successfully load a different filament which lead me to believe that the extruder assembly was suffering from dirty gears or worn out hardware. Painfully obvious, the idler gear was as smooth as a baby’s behind. Not knowing whether there were other unseen issues, I decided to purchase a whole new assembly advertised to feature hardened steel extrusion gears. . Swapping out the entire assembly including removal of all the circuit board connections proved to be time consuming (~3 hrs). However, print failures have completely disappeared as though the A1 is brand new. Print jobs that repeatedly failed over the past month are perfectly rendered using the original slicing parameters. In retrospect, it probably was not necessary to swap out the entire extrusion assembly. Rebuilding with new more robust gears would have been a much easier and cheaper path to success.
OK, I had to look at one, the coupling to the other lead screw.
This is an interesting observation, considering that they are still printed layer-by-layer, and it makes me wonder if your z belt for the non-directly-coupled screw got out of phase. Glad you got it working.