Sorry you’re having problems! Here’s my suggestions, hope they help.
1. Do you have a piece of thread stuck in the bobbin case? In the picture, I think I see a piece of tan thread at about 11 o’clock in the bobbin case.
2. When you place your bobbin, hold the thread like this:
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Then push your bobbin directly in. Never lift the lever to place the bobbin. When you pull up your bobbin thread, make sure it has not wrapped around the lever. Holding the thread like this helps prevent it from getting under the lever.
3. Completely rethread your machine. A lot of times the top thread will jump out of a disc without even realizing it, especially when changing threads and pulling them through.
4. Sounds like your bobbin winder may be winding unevenly if you’re having tension problems throughout your project. Have your dealer check it.
5. Check your bobbin for stray lint in the nooks and crannies. Trust me, this can definitely cause problems. Use canned air if needed.
6. Make sure there are no stray threads stuck in the inside section of the bobbin case area, as mentioned above. I once had a piece of thread about 6” long wrapped in there! If your machine bed has a removable section to access the bobbin area, take that off, too, and check for lint, threads, etc.
I never mess with check springs or any other part that would have to be replaced until I’ve tried all of the above and called my dealer if those don’t work. I’ve never had to replace anything yet....
Hope that helps, and good luck!