What faults can occur after a mechanical watch is dropped?

　　What kind of faults occur after a mechanical watch is dropped? When a watch is accidentally dropped on the ground, the gravitational acceleration causes significant damage. Potential damage includes external issues, such as case dents, scratches, a bent crown, or cracked watch glass; and internal issues, including dial deformation, detached indices, detached hands, or detached luminescence, as well as damage to movement components. Today, let us look at how to resolve issues with a dropped watch.

　　The stiffness, spacing, and number of coils of the balance spring are related to the oscillation frequency of the watch and the size of the movement. Generally speaking, lower frequency watches or ladies' watches have 'softer' and smaller balance springs; conversely, the higher the frequency, the 'stiffer' the balance spring.

　　In early 'slow-beat' watches (18000 beats/hour), the balance spring is most prone to 'hooking' after the watch is dropped or knocked. This is when the inner coil of the balance spring gets caught on the stud or the regulator. This usually manifests as the watch stopping or running extremely fast.

　　In modern watches, the frequency is usually 28800 beats/hour, and the balance spring is stiffer with tighter spacing. After a watch is dropped, the most common issue with the balance spring is deformation. Deformation refers to the balance spring shifting horizontally or vertically, causing it to become uneven or out of round.

　　Among these, horizontal deformation is the most common, where the balance spring loses its concentricity. Furthermore, during oscillation, it may rub against the balance spring stud. The fault manifests as the watch frequently stopping or running fast, with the degree of speed depending on how tightly the spring is pressed against the stud; in severe cases, it can gain up to 2 hours a day.

　　Many repaired watches (especially those with ETA movements) are found to have balance springs with horizontal displacement and deformation, and in every case, the second coil of the balance spring is rubbing against the stud. Repairing this requires careful correction with tweezers to ensure concentricity, proper pitch, and that it remains flat and round.

　　If you find that your watch has been accidentally dropped and it stops or runs extremely fast, it is highly likely that the balance spring has deformed. Of course, other components may also have failed simultaneously.