The Seiko A258A is a vintage quartz digital LCD movement introduced in the early 1980s. It is a direct evolution of Seiko’s multifunction A-series modules and is closely related to the A257A. The A258A powers digital watches with a combination of timekeeping, calendar, daily alarm, stopwatch, and a countdown timer, all integrated into a compact, durable module. These features made it a practical solution for users needing both day-to-day reliability and advanced time control tools.

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Technical Specifications

• Caliber Number: A258A

• Movement Type: Quartz (Digital LCD)

• Display Type: Liquid Crystal Display (7-segment layout)

• Functions:

  • Time (12-hour format)

  • Calendar (Day and Date)

  • Daily Alarm

  • Stopwatch (1/10-second resolution)

  • Countdown Timer (up to 60 minutes)

• Backlight: Not integrated (some cases featured external lighting)

• Battery Type: SR1120W (1.55V silver oxide)

• Battery Life: Approximately 2 years

• Accuracy: ±15 seconds per month

• Module Dimensions:

  • Width: ~26 mm

  • Height: ~22 mm

  • Thickness: ~5 mm

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Display Layout

The A258A features a clear, rectangular LCD layout with the following typical elements:

• Top Display:

  • Day of the week (e.g., SU, MO, TU)

  • Mode indicators such as “AL” (Alarm), “TM” (Timer), “ST” (Stopwatch), “PM” (12-hour clock), or “CH” (chime)

• Main Field:

  • Time in HH:MM:SS (12-hour format with AM/PM indicator)

  • Calendar mode shows day and numerical date

  • Stopwatch and timer use the same digit layout

This layout provides immediate access to essential information with minimal effort.

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Modes and Functions

1. Timekeeping Mode

• 12-hour format with AM/PM display

• Seconds count in real-time

• Some models feature optional hourly chime

2. Calendar Mode

• Displays the current day of the week and numeric date

• Manual adjustment required for months shorter than 31 days

3. Daily Alarm

• One alarm settable by hour and minute

• Activates an audible tone through a piezoelectric buzzer

• Alarm ON/OFF toggle

4. Stopwatch Mode

• 1/10-second resolution

• Maximum duration: 59 minutes, 59.9 seconds

• Start, Stop, and Reset functionality

• Precision suitable for casual timing, workouts, or lab use

5. Countdown Timer

• Adjustable from 1 to 60 minutes

• Beep alert sounds when countdown reaches zero

• Useful for interval timing, cooking, or task reminders

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Button Configuration (Typical)

Most watches using the A258A movement feature four side pushers:

• Button A (Top Left) – Mode selection (cycles through Time, Calendar, Alarm, Stopwatch, Timer)

• Button B (Bottom Left) – Select digits or toggle function

• Button C (Top Right) – Advance values / Start/Stop (Stopwatch or Timer)

• Button D (Bottom Right) – Reset Stopwatch/Timer or confirm selection

The button layout is generally intuitive, even without labeled functions.

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Setting Instructions

To set the time, date, or alarm:

1. Enter the relevant mode using Button A

2. Press and hold Button B to enter setting mode

3. Use Button C to increase values

4. Press Button B again to move between fields (hour → minute → second → date → day)

5. Press Button A to save and exit

Alarm and timer functions follow similar procedures but with fewer available fields.

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Battery Replacement and AC Reset

After a battery change, an AC (All Clear) reset is required.

Steps:

1. Open the case back using a suitable tool

2. Remove the depleted SR1120W battery with plastic tweezers

3. Insert a new battery with correct polarity

4. Locate the AC terminal (often labeled on the PCB)

5. Use metal tweezers to short the AC contact to the battery’s negative terminal (usually the case) for 2–3 seconds

6. LCD should flash all segments briefly, then return to default time display

Skipping this step may result in a non-functional or blank screen.

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Maintenance Tips

• No lubrication required – all-electronic movement

• Clean contacts occasionally, especially if buttons are unresponsive

• LCD fading or segment loss is common with age and usually not repairable

• Piezo buzzer can weaken over time; clean or replace contact spring if alarm volume fades

• Protect from moisture – most watches with this module were splash-resistant, not waterproof

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Watch Models and Applications

The A258A was featured in a variety of sporty digital Seiko watches, especially those marketed with a focus on functionality and ruggedness. These models were typically:

• Rectangular or tonneau-shaped

• Stainless steel or resin cases

• Top-engraved function markings

• Travel- and fitness-oriented themes

Common model numbers include A258-5000, A258-5029, and others.

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Conclusion

The Seiko A258A is a robust and practical digital movement that goes beyond basic timekeeping. Its combination of stopwatch, countdown timer, and calendar functions made it versatile for athletes, travelers, and everyday users in the 1980s. Today, it’s a prized module among vintage Seiko collectors for its unique blend of usability, clarity, and Seiko’s hallmark durability.