Overview
In some units, a defect in the filament junction can cause the backup spool to stall during a filament swap. The first roll runs out as normal, the second roll begins to load, but instead of following the runout filament into the printer, it catches inside the junction and stops. The light on that side turns blue, the printer keeps pulling the tail of the empty spool, and the new filament never enters the tube. If nudging the junction lever upward makes a small “click” and the filament immediately feeds correctly, this is the issue.
This guide shows how to correct the problem so the S1+ can perform reliable, hands-off filament changes.
Filament Junction Adjustment
Step 1: Tools Required
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Filament Junction (follow this guide to remove from s1+)
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Allen Key (2mm)
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Utility Knife
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Step 2: Disassemble Filament Junction
Following the steps in the pictures below, you’ll start disassembling the filament junction by removing the two springs and then the screws.
⚠️ There are small loose metal balls inside — do not lose them during disassembly
Step 3: Chamfer Funnel
⚠️ Be careful — the box cutter blade is very sharp.
Cut the funnel as shown in the picture below, leaving about 1 mm of space from the exit shelf (the blue section), then add a small chamfer tangent to the hole. Repeat on the other side:
Step 4: Chamfer holes
Now lightly chamfer the edges of the holes labeled in red — just enough to give them a slight angle and smooth the entry
Step 5: Clear Debris
Make sure you remove all small plastic pieces created during cutting before reassembling.
Step 6: Reassembly
Following the steps in the pictures below, you’ll reassemble the filament junction. First, place the funnel top onto the base and set the three metal balls into position. Carefully place that assembly onto the PCB, making sure the balls stay seated. Then set the whole assembly back into the junction base, reinstall the screws, add the springs, and finally reattach the junction to the S1+ using this guide.
