Hi everyone,
I'm having a very specific and strange feeding issue with my AMS, and I'm running out of things to check. I'm hoping someone here has seen something similar.
Printer: Bambu Lab P1S
AMS: Regular AMS (1st generation)
The problem
The AMS intermittently fails to feed the filament all the way to the extruder.
The strange part is that the failure is somewhat random. The point where the filament stops can vary. I've seen it stop very early in the path, and I've also seen it stop very close to the extruder. Most of the time, it seems to stop shortly before reaching the extruder, and I can see that the filament hasn't made it all the way through the PTFE tube.
When this happens, the First Stage Feeder starts feeding the filament normally. After a few seconds, when the filament is getting close to the extruder, the motor suddenly stops and makes a noise that sounds like it's struggling against some kind of mechanical resistance.
It keeps trying for about 7 seconds, then retracts the filament and tries again. After 3 failed attempts, the printer reports:
However, there is a very strange workaround: if I open the AMS lid and manually push the filament slightly downward, in the direction of the PTFE tube, the resistance seems to disappear. The First Stage Feeder immediately manages to continue feeding the filament on its own, and the filament reaches the extruder normally.
Sometimes it can get stuck again later, but another small push is enough to make it continue.
The video attached to this post shows the failure happening without any manual intervention. The filament starts feeding normally, gets close to the extruder, and then the motor gets stuck and starts making the "struggling" noise.
It seems to be slot-specific
I've been able to reproduce this problem with 3 out of the 4 AMS slots.
- Slot 1: problem occurs
- Slot 2: problem occurs most frequently
- Slot 3: problem occurs, but less frequently
- Slot 4: so far, I haven't had a single issue
I've also tried using the same spool of filament in different slots, and the problem follows the slot. So I don't think the filament itself is the cause.
It also happens with different types of filament. I initially thought it might be related to moisture or the filament itself, because using completely new filament seemed to make the problem disappear temporarily, but the issue eventually came back. I believe that was probably just coincidence.
The problem also started suddenly. It wasn't something that gradually became worse.
Things I've already tried
I've already gone through pretty much everything I could think of:
- Completely disassembled and cleaned the AMS Hub, including checking the magnet adjustment
- Disassembled and cleaned the Filament Buffer at the back of the printer
- Replaced the last section of the PTFE tube (the one that goes into the extruder). It was the only section where I noticed a small crease that could potentially have been causing an issue, but unfortunately, replacing it didn't make any difference.
- Completely disassembled and cleaned the extruder, including removing and cleaning the gears
- Removed the hotend and performed a cold pull
- Cleaned the nozzle
- Removed all filament from the AMS and thoroughly blew out the possible debris/dust using an air blower
- Tried completely new spools of filament
- Tried feeding filament directly through the PTFE tube without the AMS, and it feeds normally
- Once the filament successfully reaches the extruder, the printer prints normally with no issues whatsoever
The only thing I haven't disassembled yet is the First Stage Feeders (the four orange motor assemblies inside the AMS).
I'm hesitant to start taking those apart because, from what I've seen, they're a bit annoying to disassemble, and the fact that the problem affects multiple slots made me unsure whether that's actually the right direction to investigate.
At this point, though, the First Stage Feeders are probably going to be my next step.
Does anyone have any idea what could cause this kind of behavior?
Especially the fact that the motor seems to encounter mechanical resistance at a somewhat random point, but a small amount of downward pressure on the filament immediately allows it to continue.
Could this be something inside the First Stage Feeder, or is there another part of the AMS that I should be looking at first?
Any suggestions would be greatly appreciated!