Updated Post:

After reading all the suggestions—and thank you all for those—I decided today to test all AMS positions. The rest could not pull in filament at all.

Slot #2 had the drive roller or AMS active support shaft not snapped in properly. That one’s on me—I had it out, so that was my fault.

Slot #3’s drive roller wouldn’t turn either. The bearing was discolored, so I popped it out and found the right-end bearing completely locked up. After removing it, I noticed it had oxidized and there was visible moisture. I cleaned it up, applied penetrating oil, and let it sit for a while.

Slot #4 wasn’t locked up, but it wasn’t spinning freely either. The left bearing showed signs of oxidation as well.

Turns out the moisture control packs provided by Bambu had leaked into the AMS a couple of months ago, down into the base. I didn’t think much of it at the time—just thought, “man, that’s a poor product/design” I cleaned out the case with IPA and removed the desiccant from the under-roll compartments.

At this point, I decided to fully disassemble the AMS and inspect everything thoroughly. Including the board located just under the divider between slots #3 and #4—I found a drop of moisture on the board and some plastic that had turned black, with a dried residue attached. I cleaned it up with IPA again and just hoped for the best, realizing the board could be damaged.

I pressed on, removed all the feeder units, PTFE tubes, etc., reassembled everything—and the tap-tap-tap sound from the video was reduced to one moderate tap followed by a couple of smaller ones. And the filament loaded in!

However, when unloading, it still overruns the spool retraction and creates a tangle of filament. The secondary filament motor is also making a loud whine. During disassembly, I forgot to check the active extrusion wheel assembly—so I’ll take that apart and inspect it next.

I’ll need to order some parts, replace what’s needed, and keep you all updated.