I have a 930 and have not had your issue but thought I should mention, there is a Facebook group (if you do Facebook) for Bernina's "Vintage Bernina Sewing Machines" and another "Vintage Sewing Machines". I've seen several discussions on electrical issues with these machines so maybe it may be of help to you.
Good luck.
Hello! I am on the first group and have found it very, very helpful indeed!