Seiko 7A28 repair – Introduction to the 1st Gen British Military Seiko Chronograph.

In the early 1980s, Seiko set a new standard in horology with the revolutionary Seiko 7A28 repair The Seiko 7A28-7120 series, unveiling the world’s first analogue display quartz chronograph movement. This groundbreaking innovation not only captivated watch enthusiasts but also found its way into an extensive range of distinguished timepieces.

Comprising over 40 unique variations, the series included military watches, with some exclusively designated for the United Kingdom’s Ministry of Defence (MoD) and the South African Air Force (SAAF). Seiko’s enduring relationship with the UK’s MoD, spanning more than three decades, traces its roots back to the groundbreaking 7A28 movement. Notably, in the mid-1980s, the 7A28-7120 variant, bearing the NATO Stock Number 6645-99-768-3056, was meticulously crafted for the Ministry’s esteemed British Royal Air Force (RAF). One other notable variation was worn by Roger Moore as James Bond in A view to a Kill (7A28-7020).

From October 1984 to November 1990, the wrists of British Air Force pilots and navigators were adorned with the Gen. 1 RAF-issued Seiko watches, powered by the remarkable 7A28 movement. Soaring through the skies, these watches embodied Seiko’s commitment to precision and durability. The 7A28 movement eventually made way for the Seiko 7T27 calibre in 1993, marking a pivotal transition in Seiko’s timekeeping legacy.

With over 11,000 units produced and adorned with MoD numbers, the Seiko 7A28-7120 series stands as a rare and sought-after timepiece, weaving tales from a bygone era. Join us as we meticulously restore one of these historical watches, preserving not just its physical essence but also the extraordinary narratives it carries from a time steeped in significance. T

Seiko 7A28 Repair – This Watches History

The watch undergoing repair was originally issued in 1984 and has remained in the possession of its original owner. With nearly three decades of ownership, the timepiece has acquired sentimental value for him. Despite being in a deteriorated state with significant water ingress through the pushers, it surprisingly continued to function for some time. However, gradually, each sub-dial and the centre second hand ceased working. The final blow came when the stem of the crown rusted out, prompting the owner to bring it to the store for much-needed repair.

Seiko 7A28 Repair – Uncasing

Upon removing the case and exposing the dial, hands, and movement, it became evident that the “sandwich” dial had disassembled. Reassembling and adhering it together would be necessary during the assembly process. Fortunately, only the adhesive had deteriorated, and there was no damage to the dial coating or text, which remains in excellent condition. However, the hands exhibited some signs of aging.

The case undergoes a process where the crystal and pushers are removed. The old gaskets can then be removed. The case, caseback, pushers, and their clips are then cycled through the cleaner.

Seiko 7A28 Dirty with pushers removed

Seiko 7A28 Repair – Movement Disassembly

The process of disassembling the movement proceeded with little incident. The 5/100 second wheel and pinion were securely affixed to the mainplate. Following a thorough cleaning of the other jewel holes, the mainplate underwent a cycle in an ultrasonic cleaner, inside a jar with a cleaning solution to test if it could dislodge the 5/100 second hand from the jewel. Unfortunately, this attempt proved unsuccessful. Consequently, we procured a replacement 5/100 second hand and removed the original in two pieces.

Seiko 7A28 - movement in pieces - before clean - wellingtime seiko repairs

Seiko 7A28 Repair – Cleaning

The plates are now ready for manual cleaning, followed by a cleaning cycle along with the other components. After inspection, they will be stored until the arrival of the necessary parts. The other components for this repair include a replacement crystal, as the original suffered severe scratches, and a new stem. Opting for durability, the owner has chosen a sapphire crystal, expressing an intention to be more diligent in caring for the watch moving forward.

Seiko 7A28 Repair – Assembly

Following a brief wait for the parts to arrive, the assembly of the movement and watch can commence. The alignment of the trainplate on these 7AXX movements tends to be a bit intricate, consuming a significant portion of the assembly time.

Seiko 7A28 Assembly with new 5/100 second wheel and pinion. wellingtime seiko repairs
Seiko 7A28 - repair - 5/100second wheel and pinion

Once the movement is successfully assembled, the dial is affixed, secured by two screws. In the case of this particular dial, which was in two pieces, precise positioning is crucial and achieved through careful gluing. Utilizing the chapter ring as a guide simplifies this process, as the rear of the chapter ring features grooves that align with the dial’s edge when in the case. This makes the chapter ring an ideal alignment tool for bonding the two parts of the dial together. After allowing sufficient time for the glue to set, the hands can then be applied.

Seiko 7A28 Repair –Case Assembly

The original crown, though not lost, did have some of the stem inside, which we fortunately managed to extract. There was just enough exposed stem for a secure grip, allowing us to carefully unwind it. The new stem can now be sized and seamlessly installed. Following this, the pusher and crown are affixed with new water-resistant gaskets, and the pushers are securely clipped back onto the case. Subsequently, the case is equipped with a fresh crystal gasket, and a durable sapphire crystal is carefully fitted into place.

Seiko 7A28 Repair – Case Testing

A pressure test is conducted on the case, now equipped with a new caseback gasket, to guarantee water resistance. Once the case has dried, the movement, dial, and hands are enclosed in the case, with the crown and stem subsequently inserted. Finally, the caseback, complete with the new gasket, is securely fastened to complete the assembly.

Seiko 7A28 Repair

The 7A28 movement has variations, such as the 7A38 featuring a day-date complication and the 7A48 instead incorporating a moonphase complication. Both these models share identical wheels and pinions, although longer ones compared to those in the 7A28 highlighted in this repair blog. This additional length accommodates the space needed for the extra complications. While the 7A28 is notably rarer among these watches, the availability of parts remains fortunately quite good. More information about the models containing these calibres can be found here.

While we’ve repaired numerous Seiko ‘Age of Discovery’ watches, this marks the first WellingTime service of a military-issue 7A28. To commemorate this noteworthy event in line with the watch’s history, we’ve decided to document it on our website. This particular timepiece holds significance as the first Seiko to be sold to the British Military, featuring the pioneering analogue display quartz chronograph movement. This supply continues under the Pulsar brand another Seiko subsidiary.

We trust you’ve found the details of this Seiko 7A28 repair engaging. If you require restoration services or just a fresh set of gaskets and pressure test for your Seiko 7A28 please get in touch on the contact page or whatsapp. If you have just discovered us, we invite you to connect with us on social media for more updates. Thanks again for reading.


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