The manual is a "useful story" for longevity, emphasizing routine care to prevent common failures: How to Thread a Sewing Machine at Home – Remy Made Mar 26, 2569 BE —
Upper tension is too low OR the machine is threaded incorrectly. Fix (from manual page 14): victoria fz 7910 sewing machine instruction manualrar
: Insert the bobbin onto the spindle, secure it by pushing the lever or shifting the spindle, and use the foot pedal to wind. The manual is a "useful story" for longevity,
: Hold the upper thread loosely, rotate the handwheel toward you one full turn until the needle goes down and back up, then pull the upper thread to bring the bobbin loop to the surface. Maintenance and Troubleshooting victoria fz 7910 sewing machine instruction manualrar