Abstract: Predetermined pattern selecting and function selecting keys of an electronic sewing machine are employed for controlling the selection between normal operation of a stitch forming device and a built-in diagnosing device. The diagnosing device is enabled only when the power switch of the machine is on while the predetermined function selecting key is kept depressed, and the predetermined pattern selecting key is kept depressed for a predetermined time interval. The stitch forming device is enabled when the two predetermined keys are not depressed for the predetermined time interval.

Abstract: A stepping motor is initially set while it passes through a full moving range at comparatively low pulse frequency, and it is discriminated whether the motor moves accurately in response to driving pulses between detecting points until the motor passes one detecting point and again reaches this detecting point.

Abstract: In the invention, the sewing machine carries out winding of the thread by operating separately a thread winding mechanism and a clutch mechanism. A speed detector is provided to measure actual rotary speed of a mechanism which is related with rotation of an upper shaft. If the thread winding were carried out, while said mechanism is left as engaged with a power source of the sewing machine, the speed detector would detect the rotation of said mechanism to stop a machine motor instantaneously, so that the thread winding cannot be performed when said relative mechansim is not released from the power source, and the needle bar is not actuated at winding the thread for safety in operation.