Seiko 5931A – Technical Guide

Introduction

The Seiko 5931A is a compact, high-efficiency quartz movement developed in the late 1970s to early 1980s as part of Seiko’s 59XX series. Closely related to the 5930A, the 5931A added a date complication while maintaining a slim profile and extended battery life.

Used in Seiko’s slim quartz dress watches, especially in the Quartz Type II line, the 5931A emphasized precision, minimal maintenance, and user-friendly timekeeping, all hallmarks of Seiko’s quartz engineering philosophy.

Technical Specifications

Features Overview

Timekeeping

• Central hands for hour, minute, and seconds

• No hacking function; seconds hand continues during time setting

• High-efficiency quartz oscillator and CMOS control circuit

• Drives a low-torque stepping motor with 1-second impulses

Date Mechanism

• Quickset date using crown

  • Pull crown to position 1 and turn to adjust the date quickly

• Date advances at midnight

• No day display included in this movement

Battery and Power Management

• Uses a SR920SW (1.55V) battery

• Expected battery life: 3–5 years depending on conditions

• No end-of-life (EOL) indicator — the watch simply stops when voltage drops

AC Reset (After Battery Replacement)

After replacing the battery:

1. Locate the AC (All Clear) pin near the battery terminal

2. Use non-metallic tweezers to short the AC pin to the battery’s positive (+) terminal

3. This resets the integrated circuit and restarts the stepping motor

Failure to perform this reset may result in no hand movement despite good battery voltage.

Time and Calendar Setting

• Crown position 0: Normal (running)

• Crown position 1: Rotate to set date

• Crown position 2: Rotate to set time

⚠️ Avoid setting the date between 9:00 PM and 3:00 AM to prevent damage to the date-change mechanism.

Maintenance and Servicing

Servicing Notes

This is a non-serviceable movement at the component level. In case of motor or IC failure, replacement of the full movement is recommended.

Common Issues & Solutions

Applications and Models

The 5931A was used in:

• Seiko Quartz Type II dress watches

• Mid-range Seiko Quartz models with slim profiles

• Watch designs typically featuring:

  • Stainless steel, gold-tone, or two-tone cases

  • 34–37 mm diameters

  • Minimalist dials with baton markers

  • Date window at 3 o'clock

Caseback Reference Codes:

• Typically stamped as “5931-xxxx”

• Many models feature battery hatch backs for easy replacement

Summary Table

Conclusion

The Seiko 5931A is a reliable, efficient, and well-designed quartz movement, engineered during Seiko’s golden era of quartz development. Its slim profile, quickset date, and simple timekeeping made it ideal for dress watches in the late 1970s and early 1980s. Though relatively simple, its longevity and low maintenance needs make it a favorite among vintage collectors and an excellent candidate for restoration projects.