Seiko 3702A – Technical Guide

The Seiko 3702A is a historically notable quartz movement developed in the early 1980s. It belongs to Seiko’s family of twin-quartz calibers—designed to offer superior accuracy by compensating for temperature fluctuations, a major cause of drift in conventional quartz movements. The 3702A was primarily used in high-precision watches, including some models within the Seiko Superior and Grand Quartz lines.

This technical guide outlines the movement’s specifications, features, servicing procedures, and known performance advantages.

Movement Overview

• Caliber: 3702A

• Movement Type: Quartz (Twin Quartz / Thermo-compensated)

• Functions: Hours, Minutes, Seconds (no date)

• Battery Type: SR44W (357)

• Battery Life: ~2 years

• Accuracy: ±10 seconds per year

• Jewels: 2

• Frequency: 32,768 Hz × 2 (dual-crystal system)

Key Features

The 3702A features Seiko’s Twin Quartz system—housing two quartz crystals:

1. Primary Oscillator: Drives the step motor and timekeeping.

2. Secondary Oscillator (Temperature Sensor): Monitors temperature changes and adjusts frequency of the primary oscillator.

This setup minimizes timekeeping drift caused by ambient temperature variations, dramatically improving long-term accuracy. It was one of the most advanced quartz movements of its time.

Additional Design Notes:

• Step motor with traditional gear train.

• No calendar complication, simplifying regulation and boosting energy efficiency.

• Often found in high-grade stainless steel or gold-capped cases.

Servicing and Battery Replacement

While quartz movements are low-maintenance, thermo-compensated types like the 3702A benefit from occasional inspection.

Battery Replacement Procedure:

1. Remove case back using the correct tool (snap or screw-down).

2. Carefully remove the old SR44W battery with non-magnetic tweezers.

3. Check battery contact springs for corrosion or looseness.

4. Install a fresh SR44W, observing correct polarity.

5. Observe the second hand for precise stepping motion.

6. Re-seal the case ensuring gasket alignment for water resistance.

Service Tips:

• Never attempt to adjust the frequency manually—this is factory-calibrated.

• Avoid exposure to magnets and heat which may affect regulation circuitry.

• Do not attempt to regulate timing mechanically—corrections are automatic.

Common Issues and Troubleshooting

Due to its specialized nature, most repair shops will replace the entire movement if major faults occur.

Legacy and Accuracy

The Seiko 3702A was part of Seiko’s technological race in the quartz era to achieve “ultra-precision” in everyday wristwatches. With a rated deviation of ±10 seconds/year, it competed directly with Citizen Crystron Mega, Longines VHP, and thermo-compensated Swiss quartz calibers.

Though out of production, watches housing the 3702A remain collectible today for their:

• High-end finish

• Quiet excellence in precision

• Connection to Seiko’s innovative quartz legacy

Conclusion

The Seiko 3702A is more than a quartz movement—it represents Seiko’s relentless pursuit of accuracy in the early digital age. With its twin-quartz technology and no-nonsense two-hand display, it achieves near-atomic clock performance in a conventional analog wristwatch. For collectors and horology enthusiasts, it remains a testament to Seiko’s mastery in quartz innovation during the 1980s.