Need help. A1's linear rail locked and does not move along z-axis

Hi everyone. Ran into a problem with my new A1 and need some help. The short version: got an A1 + AMS Lite combo less than a month ago and been able to do several basic prints just fine in both Bambu’s PLA and PETG. During the print of last project, the print failed and the arm locked into place. Have tried several troubleshooting items (listed below) but nothing seems to have worked. Can’t move it up or down via any means (motor/mechanical/manual). Anyone else encounter this issue before?

More detailed breakdown:

  • Printing Bambu Lab’s AMS Lite Top Mount with PETG HF (black) filament; with 0.4 mm hotend and modified settings for PETG (slower speeds, 0.2 mm layers, 2 walls, 15% infill, etc.). Made sure to clean the plate with soap and water before print. First plate printed just fine. Second plate was about 90% complete when it failed. A few parts came loose off the plate and began to get some stringing. At the same time, the Z-axis locks into place and cannot go up or down (both X and Y axes still can move normally). The printer then enters into the following loop:

  • Toolhead moves to purge wiper;

    • Poops/extrudes filament;
    • Cuts and throws poop;
    • Hotend moves back over project and tries to print; nozzle scrapes along existing printed area for about 3 seconds
      • (assumingly because it can’t raise up on the z-axis);
    • Toolhead moves to purge wiper; repeats.
  • Based on the number of poops I found, it probably repeated this for about 30 minutes before I discovered it and stopped the print. After stopping, the printer did not return to its home position and I was not able to mechanically or manually move the rail up or down along the Z-axis. I was able to remove the plate, clear it, and clean it. I noted that the nozzle had PETG collecting around the outside of the nozzle (probably caused by scraping over printed area and the reason why it kept cycling to the purge wiper). Using touchscreen, I tried to move the toolhead up and was given an error message that it could not move the z-axis until all axes were zeroed. I then pressed the home button. Toolhead moves to center of plate along X and Y axes, but then am given an error message:

  • HMS_0300-1800-0001-0005: The Z axis motor got stuck during movement, please check if there is any foreign matter on the Z sliders or Z timing belt wheels, or if the extrusion force sensor is abnormal.

Attempted troubleshooting:

  • Tried all troubleshooting options on QR code’s page (Bambu Lab Wiki page for Error Code), including:

    • Checked for foreign objects on the Z-axis motor pulley and slider (did not find any)
    • Removed the metal base plate and inspected timing pulley and timing belt (did not find any)
    • Replaced Hotend (see below)
  • Turned on Maintenance Mode and cleaned Toolhead and hotend.

    • Did a cold pull on 0.4 mm hotend, cleared exterior hotend nozzle, and checked to make sure filament hub was clear and not blocked.
    • Tried both homing and recalibrating with cleaned hotend but got the same error message.
  • Replaced hotend with a brand new hotend (0.2 mm hotend). Tried homing and recalibrating but got the same error message.

  • Checked all wiring including rail and hotbed connector cables. No noticeable damage to any wires.

  • Tried unplugging printer for 30 minutes and restarting. No change.

When trying to look for solutions online, I’ve found similar experiences, but nothing about the rail being completely locked and unable to move at all. I’ve submitted a ticket and waiting to here back, but thought I’d reach out and see if anyone encountered this problem before. Any help is appreciated. Thanks!

Was able to resolve the issue. In the end, not exactly sure what was wrong and caused the Z-Axis to lock up and not be able to move, but what fixed it was breaking down the printer all the motor and reassembling it.

More detailed breakdown of fixing process: As the X-Axis linear rail was locked too low for me to remove the heatbed, I could only remove the bottom faceplate for the Z-axis belt (I did also loosen the belt but the rail was still locked). While there was a ton of resistance in the belt, with enough force, I was able to get the belt to rotate just a little bit. After that, it seemed to be able to go down (albeit with a lot of force), but wouldn’t go back up. I remembered reading on a forum with a similar error code on z-axis moving how someone was able to get there’s working again by manually moving it down a little and that seemed to reset it. So, I thought I’d give it a shot and see if that was enough to unlock the rail and get it moving via motor again. Sure enough, I could now control it again with the control screen! But there was a new problem. As it moved up and down, it would make a buzzing/grating sound followed by a click and repeat (buzzz click, buzzz click, buzzz click…) coming from the right screw (possibly down in the motor/belt area). At least I was able to get the X-axis rail moved all the way to the top so I could clear the heatbed and check the motor.

I secured the X-axis rail to the top with zipties and fully disassembled it again, all the way down to the belt and motor. I removed the Z-axis belt and inspected it for any nicks or breaks. I checked all the gears and could not find any obstructions (nor anything blocking the tension holes). I then removed and examined the motor, checking the interior and manually spinning the rotor. With the top of the motor casing off, the rotor did make a duck-like noise, but this went away after I put the casing back on and it spun smoothly. I honestly couldn’t find anything at this point and just put it all back together with hopes and prayers to the 3d printer gods… Plugged it all back in and EUREKA… it worked just like new. Recalibrated with no problems, printed a Benchy just to be sure, and everything seems back to normal.

Maybe the 3d printing gods were merciful and took pity on me. I’m just glad I was able to get humpty dumpty back together again and that it’s working. No better way to learn your machine I suppose than having a problem and having to take something apart.

Interesting, wonder if there was some debris in the motor that managed to clear when it was apart. Nice work.

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