Let start with common faults written by experienced mechanic
Use this section of Q & A's to find the cause of an error, then use the technical repairs section to help fix the problems.
Most computerised or basic mechanical sewing machines have the same basic components and they all use thread to form a lockstitch. Troubleshooting them is not a simple task. But with the help of a sewing machine mechanic with more then 30 years experience, it is possible to diagnose and repair a problem.
Most problems, we are talking 95% of sewing machines problems occur because of user threading errors mainly relating to thread tension errors.
The very first area to troubleshoot is threading. Make sure the machine is threaded correctly as per its instruction book. Make sure the thread go's through all threading guides, including the tension unit, the tiny wire guide just about the needle clamp, the thread take-up and the needle.
Double check to see if the needle is facing the correct direction; the rule of thumb is that the needle shank flat surface, should face away from the bobbin.