My 'older model' Brother - I have learned - likes to collect lint under the bobbin case. Between that and this small issue: unevenly wrapped bobbin thread, I think I've discovered what creates that problem for me ... at least for now. I don't like messing with either tension and will only adjust the top. I have to "watch" the bobbins as they are winding and I've slowed the speed down, also. Glad to hear you're up and running again.