Seiko 394 – Technical Guide

The Seiko 394 is a compact two-hand quartz movement from the late 20th century, designed primarily for ladies’ wristwatches and slim-profile dress watches. Built for reliability and long battery life, the 394 is part of Seiko’s efforts to miniaturize quartz technology without compromising accuracy or performance. It is known for its minimalism—lacking a second hand or calendar function—and ease of servicing.

This technical guide covers specifications, internal structure, battery replacement, and common troubleshooting tips for the Seiko 394 movement.

Movement Overview

The Seiko 394 is a two-hand analog quartz movement, displaying only hours and minutes. Its no-complication layout helps achieve excellent battery life and ultra-thin case design.

Technical Specifications:

• Caliber Number: 394

• Display: Hour and Minute

• Movement Type: Quartz

• Size: 5 ½ × 6 ¾ lignes (approx. 13.0 mm × 15.15 mm)

• Thickness: Approx. 2.00 mm

• Battery Type: SR516SW (317)

• Battery Life: ~3 years

• Accuracy: ±15 seconds/month

• Jewels: None (metal or synthetic bushings used)

The 394 is typically found in elegant Seiko-branded and licensed watches where compactness is crucial and simplicity is desirable.

Key Components and Layout

The Seiko 394 includes all standard parts of a high-efficiency quartz movement, miniaturized for compact cases:

• Quartz Oscillator (32,768 Hz): Maintains high-accuracy timekeeping.

• Integrated Circuit (IC): Converts crystal vibrations into timed pulses.

• Coil Block & Step Motor: Drives the gear train through electromagnetic impulse.

• Gear Train: Transfers power to the hour and minute hands.

• Battery Contact System: Includes a battery clamp, terminal, and insulator for stable operation.

The lack of a second hand further reduces wear and power consumption, enhancing battery life and mechanical longevity.

Battery Replacement Procedure

Battery service is simple but should be done carefully due to the movement’s small size and delicate parts.

Step-by-Step Instructions:

1. Open the Watch Case: Use an appropriate case knife or wrench.

2. Remove the Battery: Carefully lift the SR516SW using plastic or non-magnetic tweezers.

3. Inspect Battery Contacts: Clean with pegwood or a soft brush if dirt or corrosion is present.

4. Install New Battery: Insert a fresh SR516SW, ensuring correct polarity.

5. Confirm Function: Hands should begin moving within 10 seconds.

6. Close the Case: Reseat any gaskets if applicable and reseal securely.

⚠️ Important: Avoid touching the coil or integrated circuit. Use ESD-safe tools when possible.

Common Issues and Troubleshooting

Although the Seiko 394 is highly reliable, the following issues can occur over time:

Because of the movement’s low cost and modular nature, full replacement is often preferred over component-level repair.

Conclusion

The Seiko 394 is a precision micro quartz movement designed for compact, elegant timepieces. With its minimalist two-hand display, ultra-thin profile, and low power consumption, it remains a solid choice for both vintage quartz collectors and modern service technicians.

Whether you're servicing a battery or restoring a vintage ladies' watch, the 394 offers ease of handling, consistent performance, and Seiko’s trusted engineering in a very small package.