The Seiko A359A is a vintage quartz digital LCD movement released in the early 1980s as part of Seiko’s multi-alarm digital range. An evolution of earlier A35x-series modules, the A359A added refinements in usability, display clarity, and alarm control, while preserving core digital functions like timekeeping, calendar, stopwatch, and multiple alarms. Compact, efficient, and highly reliable, the A359A became a favorite in Seiko’s mainstream digital lineup and remains popular among collectors today.

Technical Specifications

• Caliber Number: A359A

• Movement Type: Quartz (Digital LCD)

• Display Type: 7-segment Liquid Crystal Display

• Primary Functions:

  • Timekeeping (12-hour or 24-hour selectable)

  • Day and Date Calendar

  • Three Independent Daily Alarms

  • 1/10-Second Stopwatch

• Backlight: Not integrated into module (some cases included a side-mounted light)

• Battery Type: SR1120W (1.55V silver oxide)

• Battery Life: ~2 years

• Accuracy: ±15 seconds per month

• Module Dimensions:

  • Width: ~26 mm

  • Height: ~22 mm

  • Thickness: ~5 mm

LCD Display Layout

The A359A uses a clean, efficient digital layout ideal for frequent function switching:

• Top Display Row:

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

  • Mode indicators:

    • “AL1”, “AL2”, “AL3” for each alarm

    • “ST” for stopwatch

    • “24H” for 24-hour format

    • “PM” for post-noon in 12-hour mode

• Main Display Area:

  • HH:MM:SS in time mode

  • MM:SS.t in stopwatch mode

  • MM-DD or DD-MM (regional variation) in calendar mode

Functional Modes

1. Time Mode

• Standard time display with hours, minutes, and seconds

• AM/PM or 24-hour indicator

• Switchable between 12-hour and 24-hour format

2. Calendar Mode

• Shows the day of the week and the date

• Manual adjustment required for months with fewer than 31 days

• Does not support leap year or year display

3. Alarm Modes

• Three separate alarms: AL1, AL2, AL3

• Settable by hour and minute

• Individual ON/OFF toggle for each alarm

• Sound output via piezo buzzer

4. Stopwatch Mode

• Measures elapsed time up to 59 minutes, 59.9 seconds

• Resolution: 1/10 second

• Includes Start, Stop, and Reset functions

Button Layout (Typical)

Watches housing the A359A module typically feature four side-mounted buttons:

• Button A (Top Left) – Mode cycle (Time → Calendar → AL1 → AL2 → AL3 → Stopwatch)

• Button B (Bottom Left) – Enter setting mode / Toggle alarm ON/OFF

• Button C (Top Right) – Increase value / Start-Stop stopwatch

• Button D (Bottom Right) – Move to next setting field / Reset stopwatch

This layout ensures fast access to all modes with minimal button presses.

Setting Instructions

To set time, calendar, or alarms:

1. Enter the desired mode using Button A

2. Press and hold Button B to enter setting mode

3. Use Button C to advance the selected value

4. Use Button D to switch between fields (e.g., hour → minute → date → day)

5. Press Button A to exit and save changes

Each alarm (AL1–AL3) is set independently in its respective mode.

Battery Replacement & AC Reset

Following battery replacement, perform an AC reset to reactivate the module.

AC Reset Steps:

1. Open the case back with an appropriate tool

2. Remove the used SR1120W battery using plastic tweezers

3. Install a fresh battery, ensuring correct polarity

4. Locate the AC (All Clear) terminal on the circuit board (usually labeled)

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

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

If skipped, the watch may remain blank or frozen.

Maintenance Tips

• No lubrication is required – the module is entirely electronic

• Clean buzzer contacts if alarm volume weakens

• Buttons may need internal cleaning if unresponsive

• LCD segment loss or ghosting is not repairable and requires module replacement

• Avoid water exposure – most models with A359A were not rated for deep water resistance

Watch Models and Usage

The Seiko A359A was used in numerous multi-alarm digital watches, typically with:

• Stainless steel or chrome-plated cases

• Printed bezel indicators for alarm and stopwatch

• Model references such as A359-5000, A359-5019, etc.

These watches were marketed globally and remain desirable for their balance of function and vintage digital aesthetics.

Conclusion

The Seiko A359A is a dependable and user-friendly digital movement that offers excellent functionality in a compact and affordable package. Its three independent alarms, clear LCD display, and easy button layout made it ideal for daily use, travel, and light sport applications. Decades later, A359A-equipped watches are still admired for their build quality, reliability, and nostalgic charm.