Seiko 5939A – Technical Guide

Introduction

The Seiko 5939A is a specialized analog quartz movement developed in the late 1970s to early 1980s. It forms part of Seiko’s 59XX series, which includes time-only (5930A), date (5931A), day-date (5932A), and day-date with 24-hour (5933A) calibers. The 5939A stands apart due to its unique multifunction layout — most notably with dual sub-dials or additional hands.

It was used in uncommon dress and multifunction watches, often JDM (Japan Domestic Market) only, and can sometimes be found in special Seiko lines like Quartz Type II, Superior, or limited editions.

Technical Specifications

Key Features

Full Calendar and 24-Hour Display

• Displays:

  • Central hour, minute, and second hands

  • Day and date at 3 o’clock (common)

  • 24-hour indicator via subdial (usually at 6 or 9 o’clock)

The 24-hour dial is AM/PM linked — not independent, and not a GMT or second timezone.

Quickset Calendar

• Crown Position 1:

  • Turn clockwise to change date

  • Turn counterclockwise to change day

• Calendar wheels often bilingual (English + Kanji or Spanish)

• Avoid calendar adjustment between 9:00 PM and 3:00 AM to prevent damage

Operation and Time Setting

• Crown Position 0: Normal run mode

• Crown Position 1: Calendar quickset (day/date)

• Crown Position 2: Time setting (hour/minute); seconds hand continues to run

The 24-hour subdial syncs automatically with the hour hand — useful for AM/PM reference.

Battery and Reset

• Battery type: SR920SW (1.55V silver oxide)

• Life expectancy: 3 to 5 years

Reset After Battery Replacement

1. Locate the AC (All Clear) pin contact (often labeled near the battery)

2. Use plastic or anti-static tweezers to short the AC pin to the battery’s + terminal

3. This resets the quartz circuit and activates the step motor

Always perform this reset after a battery change to ensure normal operation.

Servicing Notes

Movement is non-serviceable at the part level — if damaged, replacement is standard.

Watch Models Using 5939A

The 5939A was used in select Seiko Quartz Type II models and specialized JDM watches.

Characteristics:

• Stainless steel or gold-tone cases

• Day/date window at 3 o’clock

• 24-hour subdial at 6 or 9 o’clock

• Dials marked “Seiko Quartz” or “Quartz Type II”

• Casebacks marked with "5939-xxxx"

• Often featured flat mineral glass, baton hands, and minimalist styling

Some models were sold only in Japan, with bilingual day wheels tailored to the domestic market.

Summary Table

Comparison to Other 59XX Movements

Conclusion

The Seiko 5939A is a rare and feature-rich vintage quartz movement combining a classic analog layout with full calendar and 24-hour functionality. As the most complex member of the 593X family, it stands out for its practical features, durable design, and clean execution typical of Seiko’s late 1970s quartz excellence.

Collectors who find a functioning 5939A watch are encouraged to preserve it carefully, as complete working examples have become increasingly scarce.