Seiko 57B Series – Technical Guide

Introduction

The Seiko 57B series refers to a family of quartz analog movements with multifunction capabilities, particularly used in Seiko Lassale models and other premium analog quartz collections. Unlike conventional 3-hand quartz movements, these calibers often controlled time via step motors operated by a microprocessor, capable of supporting unique functions like perpetual calendars, retrograde indicators, or jumping hands.

Among the most referenced is the Seiko 57B20, a two-hand movement with no visible crown, which was used in ultra-slim watches with hidden push-button time setting.

Key Technical Variants

Commonly known versions of the 57B series include:

• 57B20A – 2-hand time-only, crownless design

• 57B30 / 57B40 – Enhanced calendar or display options

• 57B50 – Sometimes includes retrograde or jump-hour features

This guide focuses on 57B20A, with notes applicable to the rest of the series.

Technical Specifications (57B20A)

Operation and Time Setting

No Crown – Hidden Button Control

Unlike traditional quartz watches, the 57B20A has no crown. Instead, a concealed button (often on the case back or recessed into the case side) is used to control the time setting:

1. Short press – Advances minute hand by one minute

2. Long press (2–3 seconds) – Activates continuous movement

3. Press again – Stops hand when desired time is reached

A few versions allow "back-setting" by detecting long-press durations, but most advance only forward.

Power and Reset

Battery Replacement

• Uses a SR616SW (1.55V silver oxide)

• Battery life: approx. 3 years

• No EOL (end-of-life) indicator

Reset Procedure (After Battery Change)

Some models may need a reset after battery installation:

• Locate the AC pin near the battery well

• Short the AC contact to the positive terminal with non-metallic tweezers

• Hands may advance once to confirm reset

Servicing Notes

• These movements are not designed for full disassembly

• If malfunctioning, movement replacement is standard

• No lubrication is required — use dry-service practices

• Be cautious of step motor coil damage during handling

• Some versions are epoxied into cases and non-removable without damaging the watch

Common Issues

Watches Using the 57B Series

The 57B movements were most commonly used in:

• Seiko Lassale ultra-thin watches

• Crownless "button-set" dress watches

• High-end quartz Seiko International models

• Minimalist two-hand timepieces

Typical characteristics include:

• Slim, dressy cases

• Push-button time setting

• No seconds hand or date

• Often signed “Seiko Quartz,” “Seiko Lassale,” or “Japan 57B20A”

Summary Table

Conclusion

The Seiko 57B series, particularly the 57B20A, is a unique family of minimalist, crownless quartz movements that combine ultra-thin design with practical functionality. Their discreet operation, compact architecture, and reliable quartz accuracy make them an important part of Seiko’s analog quartz legacy — especially in the context of elegant dress watches and Seiko Lassale’s design-focused philosophy.