r/BMCU

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!