The Seiko H023A is a high-performance quartz movement known for powering some of Seiko’s most feature-rich ana-digi sport and dive watches during the early 2000s. It stands out with a robust combination of analog timekeeping, digital precision, and advanced chronograph functions, and it was notably used in models like the Seiko Sportura Chronograph. The H023A builds upon Seiko’s legacy of multifunction quartz innovation, offering rugged durability and enhanced usability for sports, racing, and tactical environments.

Technical Specifications

• Caliber Number: H023A

• Movement Type: Quartz (Analog + Digital Hybrid)

• Power Source: Lithium battery (CR2025, 3V)

• Battery Life: Approximately 2–3 years

• Display:

  • Analog: Hour, Minute, Seconds

  • Digital LCD: Stopwatch, Alarm, Dual Time, Calendar, Timer

• Backlight: Electroluminescent (EL)

• Jewel Count: 0 jewels

• Accuracy: ±15 seconds per month

• Size:

  • Diameter: ~31 mm

  • Thickness: ~6.9 mm

• Water Resistance (case dependent): Commonly 100M (10 bar) or more

Digital Functions

The H023A offers a wide range of digital capabilities:

• Chronograph (Stopwatch) – Measures up to 100 hours, with 1/100th second resolution

• Countdown Timer – Up to 99 minutes, with alert

• Dual Time Display – Perfect for travelers needing a second time zone

• Calendar – Full auto-calendar pre-programmed to 2099

• Daily Alarm – One programmable alarm with on/off setting

• Electroluminescent Backlight – For low-light viewing

• Time Sync Option – Manual syncing of analog and digital displays

These features make the H023A ideal for athletes, pilots, and travelers who demand quick and reliable access to multiple timing modes.

Operating the Watch

The H023A-equipped watches usually feature four buttons and a crown or pushers, depending on the model:

• Button A (Top Left) – Mode change

• Button B (Bottom Left) – Select item (e.g., hour, minute)

• Button C (Top Right) – Increase value or start stopwatch

• Button D (Bottom Right) – Reset or activate EL backlight

Setting the Digital Time:

1. Press A to cycle to Time mode

2. Hold B until the display flashes

3. Use C to adjust the value

4. Press B again to move to the next field (hour, minute, etc.)

5. Press A to finalize settings

Setting the Analog Time:

• Some models allow syncing via button command.

• Others use a crown or pusher to manually advance the hands.

• After battery changes, the analog time may require repositioning to match the digital display.

Battery Replacement and Reset

To replace the CR2025 battery, follow these steps:

1. Remove the case back using the correct tool.

2. Gently remove the old battery using non-metallic tweezers.

3. Insert a new battery, taking care not to bend contact springs.

4. Locate the AC (All Clear) contact point.

5. Using tweezers or a small screwdriver, short the AC point with the battery's negative side (typically the case) for 2–3 seconds.

6. This resets the movement and restores digital function.

Note: All data (time, alarm, etc.) will be erased after reset.

Common Issues and Troubleshooting

Movement Markings & Watch Models

The H023A is typically stamped on the metal backplate of the module. Models featuring this movement often come from the Seiko Sportura series, as well as tactical or chronograph lines from the early 2000s. These watches are often constructed from stainless steel with sapphire or mineral crystals and are built for outdoor and professional use.

Final Thoughts

The Seiko H023A is a high-utility, analog-digital quartz movement crafted for performance and practicality. Whether you're tracking split times on the track or keeping a second time zone while abroad, this movement delivers. Its rugged design, EL backlight, and reliable quartz accuracy make it a standout choice for multifunction sport watches. With proper battery care and occasional maintenance, the H023A is built to serve for years.