Maureen, Welcome to the wonderful world of machine embroidery (ME) and AnnTheGran (ATG). ME is the most fun craft, it is beautiful, and creative, you are going to fall in love when you get the machine working!
You don't say how long you have had your machine, but there is always the issue of a machine 'sitting' around for awhile. These machines manufacturered to be running with some frequency. You may have just gotten it, but it could have been on the store's shelf for some time. In that case your machine should be serviced by a technician.
We all were 'Newbies' at one time, and the problem you describe is one that plagued me for a long time. Bobbin thread that shows on top of the fabric has several causes. You have already tried the tension, so, I will assume you went up to the -5 point. That means that the top thread tension was decreased in an attempt to adjust to the bobbin.
Next, make sure that the bobbin thread, AND top thread, is threaded correctly. I suggest that you check with you manual and review that information. It is easy to miss a spot, and on that machine, I think it is #6, the wire loop.
Along the way of your journey, please read my blog on needles. Toward the end of that blog, there are files to download to check your tension. When you do your tension checks, change the needle and use differing thread brands. It will teach you a lot!
Next, change the bobbin. Some bobbins are just not wound correctly, no matter who did it.
Next, (didn't I tell you I had lots of problems?) make sure that your bobbin case area is free of lint and stray threads.
Next. and ONLY when nothing else works, find a really, really small screwdriver to adjust the screw on the bobbin case. BE CAREFUL here! Think of the screw area as if it were a round clock, and move it to the right ONLY about 5 minutes. That is a really small amount and it is intentionally small because it is not a place to be messing around a lot.
If all that fails, you may need a technician to review your machine. Sometimes only a tech can fix somethings.
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