I have also had tension problems on my sewing machine for several months. I could get it cleared up, but then it would come back. I tried all the same solutions you mentioned. I finally took out the bobbin case and cleaned it and found about a 2" length of thread that didn't show from the top. First of all, this was not mentioned in my sewing machine manual, The sewing instructor where I bought my machine showed me how it was done years ago. Now it purrs like a kitten and tension problems are nil. (knocking on the biggest piece of wood I can find!). And secondly, it took me forever to even attempt this because I have arthritis in my hands, poor eyesight, and these were tiny, tiny, tiny screws!
