BMCU370C – Port 4 causing reverse extrusion + interfering with other ports
Hi,
I’m having a strange issue with my BMCU370C and I’m hoping someone has seen something similar.
Problem description:
Ports 1, 2, and 3 are working perfectly with no issues. However, port 4 behaves incorrectly and seems to affect the other ports as well.
What happens:
- When I insert filament into port 4, it detects the filament correctly and starts feeding as expected.
- The motor direction is correct (I have double-checked this).
- However, when I start a print using port 4, it often retracts filament instead of feeding it.
- Even more strange: if filament is inserted in port 4 (even when not actively used), it can interfere with other ports.
Example:
- Printing with port 3 works fine normally.
- But if filament is inserted in port 4 at the same time, port 3 can start behaving incorrectly — it will retract when it should feed.
Important observations:
- Everything works perfectly as long as port 4 is not used or does not have filament inserted.
- The issue appears consistently tied to port 4 being active or loaded.
What I’ve checked:
- Motor direction (confirmed correct)
- Basic functionality (manual feed works on port 4 when inserting filament)
Has anyone experienced something similar?
Any help or suggestions for further troubleshooting would be greatly appreciated.
Thanks!