My Singer model 5050 has developed a bobbin thread problem, in that I have to try up to a dozen times to raise the bobbin thread. I've removed the bobbin repeatedly and detected nothing that would suggest the source of the problem, and I've rethreaded the machine several times, with no success in defining the problem. I'm eventually able to raise the bobbin thread after numerous attempts, but it's very perplexing, considering that one attempt was all I had to make in the past. Any suggestions will be greatly appreciated.
Betty