I have a Bernina 1230.
I control the thread feed to the bobbin with my finger. The thread has a path of about 8 inches from its last guide to the bobbin; I put my finger either on top of the thread or underneath to direct it towards the top or bottom of the bobbin so there is a more even wind. If more thread is winding at the top end, I place my finger on top of the thread to encourage it to move down the bobbin.