It does sound like a bobbin case problem. Threads get caught in the case and prevent it from tensioning properly. Kind of like getting dental floss stuck between your teeth.
If it's really clean but still a problem, there's usually a tiny screw on the bobbin case; turn it one way (probably clockwise) to increase bobbin tension, and counterclockwise to reduce it. Pay attention to how much you turned it, so you can do it again or undo it.
Have you tried all the usual things, including thoroughly cleaning and oiling the machine, checking for thread/ knots/ lint in the bobbin case and tension disks, changing the needle trying different thread trying a different bobbin
If you're still having trouble after all that, it sounds like something might be slipping. Maybe the drive belt is damaged and that's causing repeating problems. Or something is sticking/getting jammed. That can happen to parts that aren't on the regular oiling routine. Or when someone uses WD40 on a machine. That's a solvent, not lubricant, and can dry sticky and cause problems.
That doesn't sound like anything anybody would want in a sewing machine, so I think you have a problem. From your description, it sounds like a dirty electrical contact.
first thing I would do is (unplug the machine and) open up the foot pedal--usually just one screw holds it together, sometimes there's no screw, just invisible clamps and you pry it apart with a flat screwdriver. Clean out any lint or gunk. Check any bare metal parts, and if they're dull, sand gently with an emory board and wipe clean. Put the pedal back together, plug in the machine and see if that helps. If it doesn't, take it in for service.
Did you read the sticky at the top of the forum, "Sewing Machines, a Buyers Guide"? It's there so that the same info doesn't have to be posted for every single person who joins Craftster just to request info on buying a sewing machine. There is also a search function, so you can find all the other posts of people who joined Craftster just to request info on buying a sewing machine.
that's not a good description, so I'll use lots of words to try to make you understand.
I want to build a chandelier for my deck. Outside.
The electrical is no problem, I'm going to use strands of LED xmas lights. I even have a couple of ideas for frames--a plant stand and tomato cages.
What I'm trying to figure out is... I want to attach sea-theme shapes to the frame. Like mermaids, coral, dolphins, shells. The shapes need to stand up to sun and rain--and I live in Hawaii, so we get tons of both.
I'm kinda thinking sheet aluminum cut with a jigsaw, then gently curved to fit the frame. Another option is all that scrap acrylic sheet I've been hoarding. That wouldn't curve, but I could use smaller elements.
But painted details would be great, and I don't know what kind of metal-friendly paint would hold up to the weather. If I use the clear acrylic, it would be super cool to use a stained glass paint and have it stay translucent. Any suggestions on type or brand?
Also, I don't think my rivet gun will work with the frames I have in mind; any suggestions for attachment?
I'm still in the early planning stages (just started this morning) so really any suggestions, random thoughts, wishes, inspirational links or whatever would be welcome. I promise I won't judge.
Oooh, it just occurred to me; I'm thinking about taking a ceramics course. So if you have suggestions in that realm, bring 'em on!