HMS 0700-2000-0002-0021: Resistance, Buffer to Toolhead
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HMS 0700-2000-0002-0021 means the AMS A Slot 1 assist motor stalled because of excessive resistance in the tube between the filament buffer and the toolhead. This is the only segment that moves during a print, which makes it the one that wears.
Every layer flexes this length of tube. Treat it as a moving part, because that is what it is.
Where to buy
Carry the tube properly
A cable carrier chain takes the tube along a controlled path instead of letting it whip and fold at the same point for hours. It is the standard answer on machines where the feed has to travel, and it stops the kink forming at all.
Measure the length you actually need
A tape measure across the full travel tells you the length that reaches without slack. Too long drags and catches; too short pulls at the fittings at the end of every move.
Keep the dust out of a moving tube
An inline filament dust filter sits before this section and takes the grit off the filament before it is dragged through a flexing bore. Dust plus movement is what polishes a tube into a rough one.
Then watch it through a full layer
Run a print and look at where the tube folds. If it stops at the same spot every pass, that spot is your fault, and no amount of new tube will change it. Travel behaviour differs by machine — see printers with an AMS.
How HMS 0700-2000-0002-0021 relates to its twin
Bambu uses the same wording for HMS 0700-2000-0002-0022, which describes this segment too. If you see either, check the same length of tube.
The segment before it
From the unit to the buffer is HMS 0700-2000-0002-0019, which does not move and so fails differently. The full layout is in the AMS hub guide.
HMS 0700-2000-0002-0021 FAQ
Why does this section fail most?
Because it is the only one that flexes on every layer.
How much slack should it have?
Enough to reach the furthest point without tension, no more.
Can I lubricate the inside?
No. Anything you put in there reaches the hotend.
How often should it be replaced?
When it takes a set or feels rough. It is a wear part.
Chamber control fails quietly. HMS 0500-0300-0001-0023 means that module is malfunctioning, and nothing stops immediately, which is why people find out when an ASA part warps off the plate.
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