Planetary gearboxes, as critical components of rotary mechanical transmission systems, are extensively used in various industrial fields and mechanical devices. Failures in these gearboxes not only lead to significant economic losses but can also pose threats to the health and safety of workers. Therefore, maintaining the health of planetary gearboxes is particularly important to ensure their smooth operation and extend their lifespan. This paper utilizes On-Rotor Sensing (ORS) technology for signal collection, achieving a high signal-to-noise ratio. By comparing the single-tooth meshing count differences between the sensor's position, as determined by gravitational acceleration, and the fault gear meshing pulses, it has been discovered that the encoding of these differences, corresponding to various fault gear positions within the tidal cycle, varies. This encoding can be utilized to distinguish between different fault locations on the sun gear.