The Seiko A156A is a high-grade digital quartz movement introduced in the early 1980s, during Seiko’s peak era of innovation in LCD technology. Unlike more basic A-series modules, the A156A offered enhanced features, a more refined layout, and was often used in higher-end digital watches, including multifunction chronographs and models with dual display layouts. Known for its reliability and user-focused design, the A156A remains a favorite among vintage digital watch collectors.

Technical Specifications

• Caliber Number: A156A

• Movement Type: Quartz (Digital LCD)

• Display: 7-segment Liquid Crystal Display (monochrome)

• Functions:

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

  • Full calendar (day, date, month)

  • Daily alarm

  • Chronograph (stopwatch)

  • Timer (countdown)

  • Dual Time (in some versions)

• Backlight: Not included in the module (may be external if present)

• Battery Type: SR1120W or equivalent (1.55V silver oxide)

• Battery Life: Approx. 2 years

• Accuracy: ±15 seconds per month

• Dimensions:

  • Width: ~26 mm

  • Height: ~23 mm

  • Thickness: ~5.0 mm

Display Layout

The A156A typically features a clear and organized LCD layout:

• Main digits: Hours, Minutes, and Seconds

• Smaller segments: Day of the week (SU, MO, etc.) and calendar date

• Function indicators: Small labels for AL (alarm), CH (chronograph), TMR (timer), DT (dual time), and 24H (24-hour mode)

Display clarity and logical icon placement were key strengths of this module.

Modes and Features

The A156A supports a full suite of functions ideal for everyday use and light sport or travel applications.

Timekeeping Mode:

• Standard HH:MM:SS display

• 12-hour or 24-hour format toggle

• Hourly chime available in some models

Calendar Mode:

• Displays day, date, and month

• Manual setting required at month end

• Some variants support full-year setting (pre-programmed through limited range)

Alarm Mode:

• One daily alarm

• Audible via built-in piezo buzzer

• ON/OFF toggle via button press

Stopwatch Mode:

• Measures up to 59 minutes, 59.9 seconds

• Resolution: 1/10 second

• Start, stop, and reset

Timer Mode:

• Countdown timer (preset or adjustable depending on model)

• Audible alert at end of countdown

Dual Time (optional by model):

• Allows setting a second time zone

• Useful for travelers

Button Layout (Typical)

The module typically operates with four side buttons:

• Button A (Top Left) – Mode selector (Time → Alarm → Stopwatch → Timer → Calendar)

• Button B (Bottom Left) – Select digit or toggle function (used in set mode)

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

• Button D (Bottom Right) – Reset (stopwatch) or Confirm

Some variants may use three buttons, with combined functions depending on duration or sequence of presses.

Battery Replacement and AC Reset

To ensure proper operation after replacing the battery, an AC (All Clear) reset is required.

Steps:

1. Open the case back using an appropriate case tool

2. Remove the old SR1120W battery using plastic tweezers

3. Insert the new battery and check all contact springs

4. Locate the AC contact, usually marked on the module near the battery

5. Use metal tweezers or a small screwdriver to short the AC terminal with the battery’s negative terminal for 1–2 seconds

6. The display should flash all segments momentarily, then return to time mode

Without this reset, the display may remain blank or glitchy.

Maintenance and Troubleshooting

• LCD Fade or Segment Loss: Usually irreversible and requires a donor module

• No Sound: Check the piezo contact; clean with fiberglass pen if corroded

• Sticky Buttons: Open case and clean button contacts with isopropyl alcohol

• No Response After Battery Change: Redo AC reset; ensure fresh battery and clean terminals

Watch Models and Applications

The A156A was used in Seiko multi-function digital watches, particularly in steel or chrome rectangular cases with labeled bezels. Models included sport-themed or world time variants and travel watches sold in global markets.

These watches were marketed as advanced digital solutions for professionals, travelers, and students.

Conclusion

The Seiko A156A is one of the most capable and refined A-series digital movements. It delivers reliable timekeeping with bonus features like a countdown timer, stopwatch, and full calendar in a compact, efficient module. Whether for restoration or collection, the A156A represents Seiko’s commitment to quality digital watchmaking in the early 1980s.