Olivia's Grammy

I use my HQ16 regularly. I used it Thurs afternoon after a student had used it in the morning. Tried to use it today. The tension was very grumpy. I took the throat plate off and cleaned really,really good. Even sprayed with the mositure free air in a can. Took some of the thread off the bobbin, thinking I had filled it to full. Loosen, thighten the top thread. The bobbin thread would not pull freely. I loosen the bobbin tension a 1/2 turnnd that seem to work.................for a while. As the bobbin unwound and had less thread the problem was back only worse. I was really getting frustrated. Tightened the screw back the 1/2 turn. Kept thinking the whole time I was sewing and decided to loosen the tension for the bobbin winder. IT WORKED. How did the bobbin winder tension get tightened? Does it vibrate as I'm winding. Very frustrating.
What are your problems and solutions?