The Husqvarna Sapphire sewing machine service manual is a comprehensive guide designed for repair and adjustment of the machine. It provides detailed instructions on various aspects of the machine's functionality, covering everything from basic settings to advanced repair procedures. The manual includes sections on adjusting belt tension, setting the hook in relation to the feeding eccentric, adjusting the gap between the needle and the hook, and setting the feed dog in relation to the needle plate. It also covers adjusting the height of the hook and feed dog, setting the needle in center position, and adjusting the needle bar height. Other essential topics covered include the timing of the hook in relation to the needle, adjusting the needle threader stop, troubleshooting the threading device, and ensuring the parallelism and height of the presser foot. The manual also delves into the intricacies of stitch length balance, both in basic and advanced settings, adjusting the lower and upper thread tension, and setting the thread take-up spring. For comprehensive troubleshooting, the manual provides a detailed repair program for the Sapphire sewing machine, with specific sections dedicated to step motors, display and sensor functions, test patterns, information and test patterns, and a keyboard test. Finally, the manual includes detailed diagrams and instructions on dismantling and reassembling various components of the sewing machine, including the front lid, rear cover, front cover, base plate, power supply, circuit board, tension unit, sewing head, step motors, presser bar, needle bar, and feeding unit.