Seiko 1520A – Technical Guide (High Quality)

The Seiko 1520A is a manual-winding mechanical movement introduced in the late 1950s and used predominantly in men’s wristwatches. Known for its robust construction and reliable performance, the 1520A features a classic three-hand layout (hour, minute, and central seconds) and embodies Seiko’s commitment to precision engineering during its post-war watchmaking expansion. This movement served as a foundation for many subsequent calibers in Seiko’s mechanical lineup.

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1. Technical Specifications

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2. Key Features

• Classic three-hand display featuring central seconds

• Robust 23-jewel movement reducing friction and improving longevity

• Diashock balance staff protection enhancing shock resistance

• Reliable manual winding system with smooth crown operation

• Swiss-inspired gear train design for accurate timekeeping

• Well-finished plates and bridges reflecting quality craftsmanship

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3. Operating Instructions

Manual Winding:

• Wind the crown clockwise until resistance is felt; avoid overwinding

• Fully wound power reserve is about 42 hours

Time Setting:

• Pull the crown out to the setting position

• Rotate crown to adjust hour and minute hands

• Push crown back in to resume movement

The movement does not have a hacking seconds function; the seconds hand continues moving during time adjustment.

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4. Movement Architecture

Dial Side:

• Hour wheel, minute wheel, and cannon pinion

• Keyless works with sliding pinion and clutch wheel for time setting

Train Side:

• Mainspring barrel with ratchet and click spring

• Center, third, fourth, and escape wheels

• Pallet fork and balance wheel with flat hairspring

• Regulator lever for precise timing adjustment

• Diashock system on balance pivots for shock protection

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5. Servicing Guidelines

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6. Common Issues & Solutions

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7. Watch Applications

The Seiko 1520A was installed in:

• Men’s wristwatches with case sizes around 33–37 mm

• Polished stainless steel or gold-plated cases

• Classic dial layouts with applied indices and dauphine hands

• Timepieces branded as Seiko or Seikosha in the late 1950s and early 1960s

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8. Historical Context

The 1520A is a key movement in Seiko’s post-war development:

• One of the early high-jewel-count manual calibers

• Introduced Diashock protection to enhance durability

• Helped Seiko establish itself as a competitive watchmaker internationally

• Precursor to advanced calibers like the 1530 and Marvel series

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9. Conclusion

The Seiko 1520A is a well-built, precise manual-winding caliber emblematic of Seiko’s rise in mechanical watchmaking. Its robust construction, high jewel count, and classic three-hand design make it a favorite among vintage collectors and restorers. With proper care, the 1520A remains a reliable and elegant timekeeping solution decades after its production.

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