Recently my A1 was giving me constant errors complaining about ‘broken filament’. However there was no broken filament to be found in the printer.
What I realized however was that the printer displayed a loaded filament in extruder (green dot in the ui) even when there was absolutely no filament. So began tearing it down
What I found was that the filament sensor itself was fine; the electronics were good. However there is a little metal ‘actuator’ (not sure what to call; not a mech eng) that pushes into the sensor when the filament is loaded, and pulls away when the filament is unloaded.
However in my printer, the ‘actuator’ was stuck and would never pull away, even when the filament was unloaded; the spring that is supposed to pull it away from the sensor wasn’t working. Hence the printer always thinking filament was loaded which I think confused the system into thinking there was broken filament.
I was able to confirm it was strictly mechanical by cannibalizing this part from my out of commission A1 (waiting for heatbed) and putting it in the A1 mini; changed only that part and not the actual pcb filament sensor, and now it is working like a charm.
I submitted a request to BambuLab for a replacement part. Hoping to share this in case anybody else runs into a similar problem and my experience can help you troubleshoot!
To get to the ‘actuator’, I followed this wiki page: A1 Series Extruder Module installation tutorial | Bambu Lab Wiki (scroll down to ‘Disassembly Guide’)
I don’t know if this was wise, but I did not remove the extruder assembly from the printer itself; I was able to keep it on the printer and disassemble/reassemble to swap out the part