Seiko 5H23A Technical Guide

Introduction

The Seiko 5H23A is a well-built quartz analog movement introduced by Seiko in the late 1980s and produced through the 1990s. It’s part of the 5H family—designed for reliable, everyday use with full day-date functionality, hacking seconds, and a solid 3-year battery life. Compared to simpler quartz calibers like the 7N43A, the 5H23A is more refined in structure and accuracy, typically found in Seiko dress and field watches intended for both domestic and international markets.

The movement’s simplicity, durability, and longevity have made it a favorite among Seiko collectors and a reliable platform for vintage quartz restoration projects.

Technical Specifications

• Caliber: Seiko 5H23A

• Movement Type: Quartz analog

• Functions: Hour, minute, central seconds, day, date

• Jewels: 2

• Accuracy: ±15 seconds per month

• Battery Type: SR920SW (1.5V silver oxide)

• Battery Life: ~3 years

• Hacking Seconds: Yes (second hand stops when setting time)

• Quickset Day/Date: Yes

• Manual Reset (Zero Positioning): Yes

• Calendar Languages: Commonly English + Spanish, or English + Kanji (depending on market)

• Movement Diameter: ~23.5 mm

• Movement Thickness: ~2.9 mm

• Integrated Circuit: CMOS IC with quartz oscillator

• Temperature Compensation: No (standard crystal)

Core Features

Dual Calendar with Quickset

The day-date display is placed at the 3 o’clock position in most watch models. The 5H23A uses Seiko’s familiar dual quickset system:

• Date quickset: Rotate the crown clockwise in position 1.

• Day quickset: Rotate the crown counterclockwise in position 1.

⚠️ Always avoid adjusting the day/date between 9:00 PM and 3:00 AM, as the date-change gear is engaged and damage may occur.

Hacking Seconds

When the crown is pulled to the time-setting position (position 2), the seconds hand stops completely, allowing precise time synchronization. This feature is especially appreciated in military-style and field watches.

Manual Hand Reset (AC Pin)

The 5H23A supports a zero-position correction or hand-reset mode after a battery change or physical shock. This allows the technician or user to realign the hour, minute, and second hands to their proper zero positions.

• To perform the reset, use non-metallic tweezers or a conductive tool to short the AC contact to the positive side of the battery. This reinitializes the IC and realigns the step motor pulses.

Durability and Performance

The 2 synthetic jewels are placed at high-wear pivot points (typically the step rotor and gear train), minimizing friction and improving long-term reliability. The movement was designed with serviceability in mind and is known for decades-long performance with minimal maintenance.

Its relatively simple architecture and use of proven Seiko quartz technology make the 5H23A easy to clean, repair, or replace.

Common Applications

The Seiko 5H23A was used in a wide variety of watches during its production run, including:

• Seiko Quartz dress watches (late ‘80s to late ‘90s)

• Field-style and military-inspired Seiko models

• Seiko 5 Quartz variants (not to be confused with automatic Seiko 5)

• Two-tone, gold-tone, and stainless steel models targeting business and formal markets

These watches often feature applied indices, slim bezels, and practical day-date windows, making them versatile for daily wear.

Servicing Tips

Battery Change

• Always use SR920SW (1.5V silver oxide).

• Remove the battery gently and clean terminals to prevent oxidation.

• After replacement, always perform a manual reset using the AC pin.

Care and Maintenance

• Avoid magnetic exposure and static discharge near the integrated circuit.

• Calendar components can become brittle—always adjust carefully and never force the crown during the restricted zone.

• Spare parts are becoming rarer, so donor movements are recommended for critical replacements like the step motor, gear train, or calendar disks.

Summary Table

Conclusion

The Seiko 5H23A is a dependable quartz movement that balances practical features, durability, and ease of service. It powered a generation of robust, stylish quartz watches and continues to earn respect among vintage Seiko collectors. With hacking, quickset calendar, and hand-reset capability, the 5H23A remains an ideal platform for both restoration and daily use—even decades after its production ceased.