Seiko B337A – Technical Guide

The Seiko B337A is a digital quartz LCD movement released in the early 1990s, designed for slim, rectangular watches that emphasized clarity, minimalism, and essential digital function. It belongs to Seiko’s B-series lineup, which focused on compact digital modules ideal for everyday use, especially in formal or unisex watch designs. The B337A was built for durability, battery efficiency, and simplicity, making it a popular choice for dress-style digital timepieces.

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Movement Overview

The B337A is a digital-only quartz movement, offering the most-used timekeeping features in a streamlined, user-friendly layout.

Key Functions:

• 12-hour time display (hours, minutes, seconds)

• Full calendar (day, date, month)

• Daily alarm

• Hourly chime signal

• Stopwatch (1/100 second, up to 60 minutes)

• Backlight (LED or electroluminescent, depending on model)

Battery Type: CR2016 lithium coin cell
Battery Life: Approx. 2–3 years

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Display and Case Design

Watches using the B337A movement typically feature rectangular, flat-profile cases made from stainless steel, chrome-plated brass, or gold-tone materials. These watches are slim, lightweight, and well-suited for business, casual, or dress use.

LCD Display Characteristics:

• Large numerals for hour and minute

• Smaller digits for seconds and AM/PM indicator

• Day of the week and date display

• Mode indicators (AL for alarm, CHR for chronograph)

• Status icons for alarm and hourly signal

• Green or amber backlight for nighttime viewing

Typical Case Specifications:

• Width: 30–36 mm

• Thickness: 6–8 mm

• Crystal: Mineral or acrylic

• Water Resistance: Usually 30 meters

• Caseback: Snap-on or screw-down, marked B337-XXXX

• Strap: Stainless steel bracelet or slim leather band

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Button Layout and Operation

Most B337A-equipped watches feature a four-button layout, allowing fast access to all functions:

• MODE (bottom-left): Switches between modes — Time → Alarm → Stopwatch → Calendar

• SET (bottom-right): Activates setting mode and confirms changes

• START/ADVANCE (top-right): Adjusts digits or starts/stops stopwatch

• LIGHT (top-left): Activates the backlight

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Setting Instructions

Time and Calendar:

1. Press MODE to display the current time.

2. Hold SET until the hour starts flashing.

3. Use START/ADVANCE to adjust the value.

4. Press MODE to cycle through minutes → seconds → month → date → day.

5. Press SET to confirm and exit.

Alarm:

1. Press MODE to enter alarm mode.

2. Hold SET until alarm hour flashes.

3. Use START/ADVANCE to adjust the hour and minute.

4. Press SET to confirm.

5. Toggle alarm and hourly chime ON/OFF using START/ADVANCE in alarm mode.

Stopwatch:

• Press MODE to enter stopwatch mode

• Use START/ADVANCE to start or stop

• Press or hold SET to reset

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Maintenance and Service

The B337A is a well-built movement but requires careful handling due to its vintage digital circuitry.

Service Tips:

• Use a CR2016 battery; replace every 2–3 years

• Perform an AC reset after battery replacement (bridge AC pad to battery positive terminal using non-metallic tweezers)

• Replace caseback gasket to restore water resistance

• Avoid strong impacts, static discharge, and exposure to magnetism

• Backlight may weaken over time and is not generally replaceable

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Notable Models Featuring B337A

• Seiko B337-5000 / B337-5009 / B337-5010

• Stainless steel or gold-tone rectangular cases

• Slim, integrated bracelet or leather strap

• “Quartz LC” or “Seiko Quartz” branding

• Minimalist digital interface, often unisex

These models remain popular today among collectors and vintage watch enthusiasts for their balanced proportions, clean design, and functional simplicity.

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Final Thoughts

The Seiko B337A is a dependable digital movement designed with a focus on clarity, ease of use, and refined styling. It represents the best of Seiko’s early 1990s digital design—offering useful features in a slim, discreet form. Whether you're restoring a vintage piece or wearing it daily, the B337A delivers long-term reliability and timeless appeal.

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