The Seiko A159B is a refinement of the earlier A159A digital quartz module, offering similar functionality but with slight improvements in component layout, power regulation, or interface logic. Produced in the early to mid-1980s, the A159B was part of Seiko's mainstream digital lineup and appeared in many daily-wear rectangular LCD watches. It’s known for reliability, straightforward operation, and long service life—qualities that helped Seiko dominate the digital watch market in that era.

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Technical Specifications

• Caliber Number: A159B

• Movement Type: Quartz (Digital LCD)

• Display Format: 7-segment Liquid Crystal Display

• Functions:

  • 12-hour time (HH:MM:SS)

  • Calendar (Day of week and Date)

  • Daily alarm

  • Stopwatch (1/10 second resolution)

• Backlight: Not integrated into module (some cases included external light sources)

• Battery Type: SR1120W (1.55V silver oxide)

• Battery Life: Approx. 2 years

• Accuracy: ±15 seconds per month

• Dimensions (Module):

  • Width: ~26 mm

  • Height: ~22 mm

  • Thickness: ~5 mm

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Display Layout

The Seiko A159B features a familiar and practical layout:

• Main Display: Time shown in HH:MM:SS with AM/PM indication

• Top Row or Corner: Day of the week (e.g., MO, TU, WE)

• Indicators: Mode cues such as “AL” (alarm), “ST” (stopwatch), and “PM” (afternoon)

The segment display is designed for clear, high-contrast readability under normal lighting conditions.

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Operating Modes and Features

1. Time Mode

• Standard 12-hour time display

• Hours, minutes, and seconds

• AM/PM indication

• Time can be set manually via set mode

2. Calendar Mode

• Displays day of week and date (day of month)

• No automatic correction for different month lengths

• Manual adjustment required for months with fewer than 31 days

3. Alarm Mode

• Daily alarm

• Alarm ON/OFF toggle

• Set hour and minute for alarm independently of main time

4. Stopwatch Mode

• Maximum measurement: 59 minutes, 59.9 seconds

• Resolution: 1/10 second

• Start, stop, and reset functions

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Button Layout (Standard Configuration)

Watches equipped with the A159B movement typically have four side buttons:

• Button A (Top Left) – Mode selection

• Button B (Bottom Left) – Set or select (in setting mode)

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

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

The buttons are clearly labeled or intuitively placed on most models, often with engraved bezel indicators.

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Setting Instructions

To set time and date:

1. Press Button A to enter time mode

2. Press and hold Button B to enter the setting mode

3. Use Button C to change values

4. Use Button B again to move through setting fields (hours, minutes, date, day)

5. Press Button A to confirm and exit

This method ensures quick, intuitive setup.

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Battery Replacement and AC Reset

After battery replacement, a full reset of the module is necessary to restore normal function.

Reset Procedure:

1. Remove the back case using the correct tool

2. Extract the depleted SR1120W battery with plastic tweezers

3. Insert a new battery carefully, checking contact pressure and polarity

4. Locate the AC (All Clear) terminal on the circuit board (often marked “AC”)

5. Short the AC terminal to the battery’s negative terminal (usually the case body) using metal tweezers or a screwdriver

6. Watch for a full segment flash followed by return to the default time mode

Skipping the AC reset may leave the display blank or non-functional.

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Maintenance Notes

• No lubrication required – this is a fully electronic system

• LCD aging is common (segment fade, contrast loss), which may require module replacement

• Buzzer contact may oxidize over time—clean with fiberglass pen if alarm fails

• Water resistance is generally limited on A159B-cased watches; avoid full immersion

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Applications and Watch Models

The Seiko A159B was installed in a variety of rectangular digital watches with stainless steel or chrome-plated resin cases. Common model references include:

• A159-5000, A159-5019, and other variants

• Watches labeled “Alarm Chronograph” or “Quartz Digital”

• Daily-use watches with metal bracelets or resin straps

These models were known for rugged construction, affordable pricing, and simple servicing.

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Conclusion

The Seiko A159B quartz digital movement reflects Seiko’s dedication to durable, affordable digital technology in the early 1980s. With time, alarm, calendar, and stopwatch functions in a compact and user-friendly format, it remains a favorite for vintage digital collectors and watch enthusiasts. When properly maintained, the A159B continues to perform well—even decades after its debut.

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