The Seiko A135A is a vintage digital quartz movement introduced in the early 1980s. It is part of Seiko’s A-series of LCD modules and was used in entry-level to mid-range digital watches. The A135A offered a familiar but useful suite of digital functions, including timekeeping, calendar, daily alarm, and a 1/10-second stopwatch. Built for reliability and easy operation, this module served as a dependable digital engine during Seiko’s rapid advancement in LCD technology.

Technical Specifications

• Caliber Number: A135A

• Movement Type: Quartz (Digital LCD)

• Display: Digital (7-segment LCD)

• Functions:

  • Time (12-hour format)

  • Calendar (Day of the week and Date)

  • Alarm

  • Stopwatch (1/10 second)

• Backlight: None (backlight not integrated into module)

• Battery Type: SR1120W (1.55V silver oxide cell)

• Battery Life: Approximately 2 years

• Accuracy: ±15 seconds per month

• Module Dimensions:

  • Width: ~26 mm

  • Height: ~22 mm

  • Thickness: ~5 mm

Display Layout

The LCD screen of the A135A movement typically includes:

• Main Display: HH:MM:SS (hours, minutes, seconds)

• Upper or Side Display: Day of the week (e.g., SU, MO, TU)

• Secondary Indicators: Mode markers such as “AL” for alarm, “ST” for stopwatch, and “PM” for afternoon times (in 12-hour format)

Functions and Modes

The Seiko A135A was built to cover daily timekeeping needs with a simple interface.

Timekeeping Mode:

• Displays time in 12-hour format

• AM/PM indicated via segment display

• Hourly chime on/off (varies by model)

Calendar Mode:

• Shows day of the week and date (DD)

• No automatic month-end correction or leap year adjustment

• Manual date advancement required at the end of short months

Alarm Mode:

• One daily alarm with piezo buzzer tone

• Alarm ON/OFF toggle accessible in alarm mode

Stopwatch Mode:

• Measures elapsed time up to 59 minutes, 59.9 seconds

• Accuracy: 1/10 second resolution

• Start, Stop, and Reset functions using designated buttons

Button Layout (Typical)

The A135A-equipped watches generally feature three or four buttons:

• Button A (Top Left) – Mode selector (cycles through time, alarm, stopwatch, calendar)

• Button B (Bottom Left) – Set/select digit (or toggle feature, depending on mode)

• Button C (Top Right) – Start/Stop (in stopwatch), Increase (in setting modes)

• Button D (Bottom Right, if present) – Reset stopwatch or toggle alarm/chime

Some variants simplify this to a three-button setup, combining multiple functions.

Battery Replacement and AC Reset

To ensure proper functionality after battery replacement, the movement must be reset using the AC terminal.

Steps:

1. Open the case back carefully using a suitable tool

2. Remove the old SR1120W battery with plastic tweezers

3. Insert a new battery, ensuring proper polarity

4. Locate the AC (All Clear) terminal on the module (usually marked)

5. Using tweezers or a metal tool, short the AC contact with the battery’s negative terminal for 2–3 seconds

6. The screen should flash all segments momentarily and return to default mode

Failing to reset may result in a blank or non-responsive display.

Maintenance Tips

• LCD Issues: If segments are missing or appear faded, it could be due to age or degraded zebra strip/contact

• Alarm Problems: Clean the piezo buzzer contacts if no sound is heard

• Button Failure: Corroded internal contacts or dust buildup can affect response; clean carefully

• Water Exposure: Most A135A-based watches are not highly water-resistant—avoid submersion

If the IC or LCD fails completely, sourcing a donor movement is typically the only repair option.

Applications and Watch Models

The A135A was installed in a variety of Seiko digital watches from the early to mid-1980s. These included:

• Square and rectangular LCD models

• Stainless steel or chrome-plated resin cases

• Watches sold globally under the Seiko Quartz Digital or Seiko Alarm Chronograph lines

These watches were built for practical use, with easily readable displays and simple button layouts.

Conclusion

The Seiko A135A digital movement exemplifies the functional simplicity and durability of Seiko’s early quartz LCD watches. With essential features like alarm and stopwatch, it offered everything a user needed in a reliable, easy-to-use format. Today, it remains a nostalgic and collectible module for enthusiasts of vintage digital timepieces.