The Seiko S240A is a multifunction analog-digital quartz movement crafted for watches requiring advanced functionality in a tactical, field, or sport setting. As one of Seiko’s latest-generation ana-digi calibers, the S240A offers a refined balance between classic analog legibility and modern digital utility, built with a focus on user-friendliness, accuracy, and field durability.

Used in a variety of robust Seiko models, the S240A powers watches often selected by adventurers, military personnel, athletes, and global travelers. It features essential tools like a chronograph, dual time, timer, alarm, and backlight—all in one compact, serviceable module.

Overview

The Seiko S240A is part of the brand’s evolution of S-series hybrid movements. It takes the reliable platform of previous models like the S234A and S229A, then adds enhanced power efficiency, more responsive push-button controls, and improved LCD contrast for better readability in all environments.

With independent analog and digital time displays, the S240A provides flexibility for those operating across multiple time zones or requiring a separate timing reference—making it ideal for travel, field duty, and mission timing.

Key Features

• Analog Time Display: Central hour and minute hands (no analog seconds in most models).

• Digital LCD Display: High-contrast screen with segment layout optimized for quick readability.

• Chronograph: Measures up to 100 minutes with 1/100-second accuracy.

• Countdown Timer: Programmable for up to 99 minutes.

• Daily Alarm: Audible alert with on/off function.

• Dual Time Display: Second time zone via digital interface.

• Full Auto Calendar: Pre-programmed through 2049 or later.

• 12/24-Hour Format: Toggle between standard and military time.

• Electro-Luminescent Backlight (EL): For nighttime or low-light use.

• Battery End-of-Life (EOL) Indicator: Display dimming or blinking when battery is low.

This combination makes the S240A a field-ready hybrid for a wide range of practical applications.

Technical Specifications

• Caliber: Seiko S240A

• Movement Type: Quartz (analog-digital hybrid)

• Battery Type: SR927W (1.55V silver oxide)

• Battery Life: Approx. 2–3 years (depending on alarm/light use)

• Accuracy: ±15 seconds per month

• Jewel Count: 0

• Dimensions:

  • Diameter: Approx. 30.0 mm

  • Thickness: Approx. 6.2 mm

• Hand Hole Sizes:

  • Hour: 1.10 mm

  • Minute: 0.65 mm

Its size is optimized for rugged mid-sized watch cases (typically 40–45 mm in diameter).

User Controls

Watches equipped with the S240A generally use a crown for analog time setting and three or four pushers for digital controls.

Crown:

• Pull to set analog hour and minute hands (no interaction with digital time).

Buttons (typical layout):

• A (Top Left): Switches between modes (Time → Chronograph → Timer → Alarm → Dual Time → Calendar).

• B (Top Right): Start/Stop or increase values during setup.

• C (Bottom Left): Reset (for chronograph/timer) or activate backlight.

• D (Bottom Right): Enter/exit setting mode or toggle 12/24-hour format.

Digital and analog time displays are independent, allowing each to be set separately if desired.

Servicing and Maintenance

Battery Replacement:

• Use only a SR927W battery.

• After battery installation, always perform an AC reset.

  • Bridge the AC contact with the battery edge using metal tweezers to reactivate the digital system.

• Test all digital functions and backlight before resealing.

Analog Time Adjustment:

• Use the crown to align the hour and minute hands.

• Analog and digital displays must be manually synchronized if needed.

LCD Display Check:

• Test full segment visibility.

• If fading or missing segments are present, replace the entire movement module—LCD panels are not individually serviceable.

Gaskets and Sealing:

• Always replace caseback and pusher gaskets when opening the watch.

• Use silicone grease and pressure test if water resistance is claimed.

Common Issues

• Blank Digital Screen After Battery Change: Usually caused by skipping the AC reset.

• Backlight Failure: Caused by low battery or expired EL panel (not user-replaceable).

• Analog-Digital Mismatch: Set both displays manually; they operate independently.

• Sticky Pushers: Often caused by dirt or gasket wear—clean thoroughly and inspect springs and seals.

• Quick Battery Drain: Due to excessive use of light/alarm, or use of incorrect battery type.

Conclusion

The Seiko S240A is a modern, field-oriented quartz movement that skillfully blends analog elegance with digital power. It’s designed for users who need tools like a stopwatch, timer, alarm, and dual time while still appreciating the legibility of classic analog hands. With strong reliability, easy servicing, and excellent user interface design, the S240A continues Seiko’s reputation for practical, mission-ready hybrid movements. Whether for outdoor adventure, global travel, or professional use, it’s a trusted choice in the world of multifunction watches.