Seiko 5Y91A Technical Guide

Overview

The Seiko 5Y91A is a sophisticated quartz chronograph movement introduced in the early 2000s. It combines precise quartz timekeeping with advanced chronograph functions, making it suitable for sporty and multifunctional watches. The 5Y91A features stopwatch capabilities with 1/20-second accuracy, elapsed minutes tracking, and a date complication, providing versatility and reliable performance.

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Specifications

• Caliber: 5Y91A

• Movement Type: Quartz chronograph

• Jewels: None (typical for quartz movements)

• Frequency: 32,768 Hz (quartz crystal oscillator)

• Power Source: Battery (silver oxide or lithium)

• Functions: Hours, minutes, central seconds, 1/20-second chronograph, elapsed minutes, date display

• Additional Features: Split time (lap) function, flyback reset, quickset date adjustment

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Movement Architecture and Components

Quartz Crystal Oscillator

Oscillates at 32,768 Hz, providing a stable and precise time base.

Integrated Circuit (IC)

Controls the division of the quartz signal and manages chronograph and timekeeping functions.

Stepper Motors

Multiple stepper motors independently drive timekeeping and chronograph hands for simultaneous operation.

Gear Train

Transmits mechanical motion from the stepper motors to the watch hands with precision.

Calendar Module

Date wheel with quickset feature for easy manual adjustment via the crown.

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Operation

The quartz crystal generates a stable oscillation signal. The integrated circuit divides this frequency and sends pulses to the stepper motors, which advance the hands accurately. The chronograph measures elapsed time with 1/20-second increments and tracks minutes elapsed. The split time function allows intermediate timing without stopping the main chronograph. The flyback reset enables instant reset and restart of the stopwatch. The date advances automatically every 24 hours and can be manually adjusted.

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Servicing and Maintenance

• Battery Replacement: Recommended every 2 to 3 years; use the specified battery type.

• Cleaning: Maintain case seals to protect the movement from dust and moisture.

• Lubrication: Minimal; light lubrication may be necessary on gear train components during servicing.

• Common Issues: Battery leakage, IC failure, stepper motor wear, and button wear.

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Summary

The Seiko 5Y91A quartz chronograph movement offers precise and versatile timekeeping with advanced stopwatch functions. Its robust design and reliable performance make it suitable for sporty and multifunctional watches. Proper battery care and regular servicing help ensure long-term accuracy and durability.

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