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The Seiko 7A28 is an analog quartz chronograph movement introduced around 1983 and used in Seiko Sports 100 watches. Watch references describe it as the first analog quartz chronograph movement; that milestone is best understood as an attributed historical claim, not a reason to assume every watch bearing the 7A28 name is identical. This is a reference-based guide, not a hands-on review of a particular watch: no individual example was inspected or tested.
What is the Seiko Sports 100 7A28?
The 7A28 is a quartz movement that drives conventional analog hands and chronograph functions. It is associated with Seiko Sports 100 watches, and sources place its introduction or approximate production start around 1983. Mizeni’s movement reference lists 15 jewels, a 32,768 Hz frequency, and a silver-oxide SR936SW / 394 battery. These are reference specifications; confirm the movement and battery requirement in the watch in question. Mizeni’s 7A28 reference
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Solar Chronograph Speedtimer by Seiko | $695.00 | Buy on Amazon |
| Movement-reference item | Listed detail |
|---|---|
| Type | Analog quartz chronograph |
| Jewels | 15 |
| Frequency | 32,768 Hz |
| Movement diameter | 29.0 mm |
| Movement height | 3.5 mm |
| Battery | SR936SW / 394 silver-oxide |
| Calendar | No day/date listed for the 7A28; the related 7A38 is listed with day/date |
All figures in the table are from Mizeni’s movement reference; its publication year is not stated. Movement dimensions are not the external dimensions of a particular case. Mizeni’s 7A28 reference
Was the 7A28 the first analog quartz chronograph?
Several sources describe the 7A28 as the first analog quartz chronograph movement, with its arrival dated to about 1983. The careful phrasing is “described as the first”: the accessible material supports reporting that historical attribution, but does not provide an official Seiko statement or a primary historical document establishing the superlative independently. The milestone is part of the movement’s significance, not proof that a particular surviving watch is original, complete, or in working order.
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What can the chronograph do?
An accessible third-party operating guide describes start/stop timing, a reset control, split or lap timing, and adjustment of chronograph hands that do not align at zero. The exact arrangement should be checked on the individual watch and against suitable documentation before operating it; the guide is not an official Seiko manual. Vintage Eye Watches’ 7A28 operating guide
Controls described in the guide
- The top-right pusher starts and stops the chronograph.
- The bottom-right pusher resets it after stopping.
- The top-left pusher operates split/lap timing.
- The guide sets the time with the crown pulled to its second click.
These descriptions apply to the guide’s control layout, not necessarily every case configuration. Avoid forcing a crown or pusher if its function is uncertain.
Correcting a chronograph hand that misses zero
The guide describes pulling the crown to its first click and pressing a pusher to correct a misaligned chronograph hand. It does not establish one universal correction sequence for every reference or explain every possible hand position. Check the specific watch’s instructions, and have a watchmaker investigate if the hands will not align or a pusher behaves unexpectedly.
Can a vintage 7A28 be serviced?
Vintage Eye Watches describes the movement as using an all-metal gear train and as designed to be regulated and repaired. That supports the practical view that a capable watchmaker may be able to service it; it does not guarantee that replacement parts, expertise, or local service are available for a given example. Ask a watchmaker experienced with vintage Seiko chronographs to assess the actual movement before budgeting for a repair. Vintage Eye Watches’ 7A28 operating guide
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“Sports 100 7A28” is not enough information to establish the condition or originality of an individual watch. Reference, dial, hands, case, bracelet, and movement details can vary, and a retailer listing documents only its own example. For a purchase or collection assessment, record the evidence for the exact watch rather than generalizing from a model description.
- Read the caseback reference and serial, and verify the movement identity.
- Check timekeeping and each chronograph function, including whether the hands return to zero. Treat this as a functional check, not an accuracy test.
- Inspect the dial, hands, case, and bracelet for condition and signs of replacement; request clear photographs where an in-person inspection is not possible.
- Ask for battery replacement and service records, and note any parts that are not original.
- For a documented elapsed-time accuracy check, state the duration and comparison instrument. No such test was performed for this article.
A retailer listing describes one 1983 7A28-7000 example with a 15-jewel movement and 1/10-second, 30-minute, and split-time functions. Those details describe that listing, not every 7A28 watch or the uninspected watch a reader may be considering. Its listed sale price is not evidence of general market value. Retailer listing for one Seiko 7A28-7000 example
How to compare a 7A28 with another vintage chronograph
Compare the particular watches, not just their reputations. The 7A28’s quartz operation and documented chronograph features offer a different experience from a mechanical chronograph; neither makes it categorically better. Evaluate the exact reference and dial, originality of case and bracelet, operation of every register and pusher, service documentation, parts access, and the seller’s return or guarantee terms.
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Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
