This comes as sort of a follow up to a thread yesterday. I wasn't too keen on posting it on the open board as I do NOT wish to come across as trying to be a "know it all". I just hate seeing people send their machine to the shop for two weeks, or totally give up on it.
There are two manuals for sewing machines, one is an Operator's Manual, which comes with the machine. The Operator's manual is just that, how to sew with the machine.
The other manual is a REPAIR Manual. That is the one that is a national secret. (Hey, repairmen have to earn a living too!) This manual tells you how to FIX the machine. You can Google to find a Repair Manual for your specific machine. Usually available for around $10-12. Voila, there's your magic.
This info DOES come with a disclosure. I am NOT an expert on sewing machines. (Or anything else except chocolate.) My husband has ALWAYS repaired my machines using this method. My BIL does the same. My machines have NEVER been in the shop for repairs and I've been sewing, well, for a hundred years. Further, we've had no issues with my computerized machines, so the above information has NOTHING to do with the computerized machines.