Thread breakage or shredding can occur in any embroidery machine, including the Brother SE1900 Sewing and Embroidery Machine. Here are some steps you can take to fix this issue:

1. Check the needle: Make sure the needle is the correct size for the thread being used and is inserted properly. A bent or dull needle can also cause thread breakage.
2. Check the thread: Ensure that the thread is not old, brittle or too thick for the needle. Thread that is wound too tightly on the spool can also cause thread breakage.
3. Check the tension: Incorrect tension can cause thread breakage or shredding. Make sure the thread is threaded properly through the machine and the tension is adjusted correctly.
4. Check the bobbin: Ensure that the bobbin is wound correctly and is not too loose or too tight.
5. Check the machine settings: Make sure the embroidery design settings are appropriate for the thread and fabric being used. Also, make sure the machine is clean and free from any debris or lint.
6. Try a different brand of thread: If the above steps do not work, try using a different brand of thread as some threads may be more prone to breakage than others.

If none of the above steps work, it may be best to take the machine to a qualified technician for further inspection and repair.