The Seiko F231A is a compact, analog quartz movement designed for slim and elegant wristwatches. Developed by Seiko during the peak of their quartz innovation era, this movement is a close relative of other members in the F-series. It is commonly found in smaller dress watches, especially women’s models, due to its minimal thickness and small dimensions. While it lacks complications, its precision and simplicity make it a dependable movement for basic timekeeping.

Specifications

• Display: Analog (three-hand – hour, minute, second)

• Movement Type: Quartz

• Caliber Number: F231A

• Jewel Count: 0 jewels

• Battery Type: SR521SW (1.55V silver oxide battery)

• Battery Life: Approx. 2 years

• Accuracy: ±15 seconds per month

• Size: 5½ lignes x 6¾ lignes (approximately 12.8 mm x 15.3 mm)

• Thickness: Around 2.5 mm

• Hand Fitting Dimensions:

  • Hour: 1.00 mm

  • Minute: 0.60 mm

  • Seconds: 0.17 mm

This ultra-compact size and low profile make the F231A ideal for slim cases where space is limited. It is often used in minimalist Seiko dress watches without complications such as a date or day window.

Time Setting Instructions

The movement features a traditional single crown control:

1. Normal Position (Pushed In) – Watch runs continuously.

2. Pulled Position – Stops the hands and allows manual setting of the time. Rotate the crown to move the hour and minute hands.

There is no hacking feature, so the second hand continues to run during time adjustment unless the movement stops completely due to battery removal.

Servicing Tips

Although the F231A is a low-cost, non-jeweled movement, proper handling during service is crucial:

• Always use anti-static and non-magnetic tools.

• Handle the battery replacement with care to avoid damaging the contact springs.

• Clean the contact points using a fiberglass brush if oxidized.

• Apply light watch grease at the contact spring base to prevent future corrosion.

• After replacing the battery, short the AC terminal to the battery for a hard reset if the movement doesn’t restart immediately.

Because the movement is simple and modular, replacing the entire movement is often more cost-effective than repairing individual components.

Common Troubleshooting

• Movement Not Starting: Check for a dead battery, loose battery contact, or oxidation.

• Hands Sticking or Misaligned: May require realignment or cleaning of the pinions.

• Second Hand Skipping or Jerking: This usually points to a coil problem or excessive resistance in the gear train.

Visual Identification

The movement is marked “F231A” directly on the main plate or near the battery well. You may also find “SEIKO TIME CORP.” stamped, denoting its authenticity. The layout is a classic Seiko compact design—minimalist with an efficient structure.

Final Notes

The Seiko F231A is a fine example of Seiko’s approach to creating accessible, low-maintenance quartz movements for fashion-oriented timepieces. Though it may not feature complications or jewels, it offers solid timekeeping performance in a very small footprint. Whether servicing a vintage Seiko dress watch or sourcing a replacement, the F231A remains a functional and affordable solution.