AMS2 Pro - Filament not detected at extruder

user_2305163143 · April 10, 2025, 12:08am

Hi everyone. H2D combo owner, but having issues with the AMS 2.

The AMS will feed filament into the extruder fine, but every time it will then retract the filament. It will do this 3 times, then error out with: The filament buffer signal is abnormal; the spring may be stuck, or the filament may be tangled [0700-4000-00014 184702].

Occasionally it looks like the filament buffer will get stuck when the AMS attempts to retract the filament, then “pop” it loose after some tesnion (video below). This does not happen every time so does not appear to be the root issue. I am not using any exotic filaments, all are brand new Bambu PLA basic. The printer works absolutely fine without the AMS by feeding filament from the spool holder (proof).

Here are some videos and pictures that demonstrate the issue:

Here is a list of everything I have tried:

Both left and right extruder
Various Bambu PLA basic filaments, including cutting ends off and checking angles on the ends of the filaments
There are definitely no kinks or snags on the filament reel, it feeds nicely
All slots in the AMS
Removed and replaced all PTFE tubes. I have checked all the lengths on the tubes and ensured that they are all correctly inserted. I have checked that the end of the tube into the extruder has a nice cut (proof)
Various PTFE tube lengths and angles from the AMS
Manually fed filament from the AMS PTFE tube to the extruder. There is no resistance, no snags, no debris, nothing getting caught. The filament slides nicely all the way into the extruder and there are no marks when I check the filament afterwards to suggest anything is scraping
The filament buffer springs look fine, and the PTFE tube is inserted all the way. I can slide the spring backward and forward without any problem (proof)
Replaced the hot end on the extruder with the included spare
Reset the connection between the AMS and the printer
Both connection ports on the back of the AMS
Checked the contact patches on the AMS cable, and used a voltmeter continuity test to confirm connectivity on each contact patch
Updated to the latest firmware
Marked on some white filament a measure to confirm that the AMS is feeding filament all the way into the extruder (proof)

I’m not really sure what’s left for me to try to isolate the issue. From the wiki it doesn’t look like there’s a sensor inside the AMS that checks if the filament has been delivered, instead this is all done by the filament buffer on the printer. So that leads me to believe that it’s either the filament buffer sensor (which all looks to be on the PCB, which would explain why both extruders fail), or some kind of chip in the AMS that receives the signal. When I feed filament manually and the printer asks to insert the filament, it detects when this is done and picks it up and extrudes automatically.

Has anyone else had this issue or can think of anything else I can try? I do have a ticket open, but it’s been 8 days now and despite various logs, pictures, videos and all my troubleshooting steps above so far all I’ve received has been to check if the nozzle is clogged. The printer itself has been fantastic and the prints I’ve done so far have come out great.

iChris · April 10, 2025, 12:47am

I encountered a few similar issues on the P1 and X1 printers. The AMS units would push the filament directly to the extruder and halt. In my case, this was typically due to friction somewhere within the PTFE tubes. To alleviate some of the strain on the AMS feeding motor, you could try unrolling the spool while it’s loading. Additionally, I found that a factory reset was helpful on the P1P.

user_2305163143 · April 10, 2025, 12:50am

Thanks for the response. I’m a little hesitant to cut the tube (even though it’s just PTFE) without support asking me to do so first, as I’m still within my return window. Comforting to know it’s not just me, I haven’t seen any other posts yet with this issue (although early days with the H2D).

user_2305163143 · April 10, 2025, 12:53am

Hey thanks for the response. I’m pretty confident the feed tubes are OK as I’ve tried and tested a few different lengths, angles, filament etc and it seems OK to me.

I do want to attempt a factory reset but the message about the plate being center put me off. I know the green home icon on the bed leveling screen sets it, but this brings the plate very high, just below the nozzle. After a print the plate sits center which looks like it would be right so that’s left me a little confused as to which is best. There doesn’t appear to be a wiki article about performing a factory reset for the H2D (yet?).

iChris · April 10, 2025, 1:07am

Yeah, should not be the case with your setup and the default PTFE tube lengths.
But it’s worth a try to see if its the strain on the filament path or something sensor related.

You can always move the plate down manually after homing it, or even without homing it. (4 right buttons on the XYZ Motion screen) Should be fine to move it down just a bit. The message is just to make sure the plate is not running into either the bottom limit or toolhead while waiting for feedback from the motion system.
Once you have the plate somewhere in the middle, you should be safe to perform the reset.

user_2305163143 · April 10, 2025, 1:17am

Ok thanks. I’ve got 2 hours left on a print and then I will level it up and give a full reset a go.

user_2305163143 · April 10, 2025, 4:07am

Reset complete, but it did not fix the issue unfortunately. However, I did capture the AMS setup screen where all sensors are happy with the filament sent from the AMS (proof).

I think that indicates a problem with the filament buffer, and support seem to agree as they have responded to my ticket indicating that the buffer spring assembly has an issue and will send a replacement.

user_1419251669 · April 15, 2025, 4:19am

I’m having the same issue. I suspect it’s the buffer hub. When I feel the tension on the the sliders, they feel different. When they are at rest with no filament loaded, they end up in different positions. Still waiting for support since Friday. This is only on the left hotend. The right end works fine.