SEIKO 7A28 Movement – What’s Inside?

By October 16, 2017Uncategorized

This photo shows inside the SEIKO 7A28 movement. Here you can see the keyless works, micro motors and gear train that operate the watch.

Each of the copper coils runs a tiny motor that operates each hand on the watch. In the middle, the gear train does to work to run the minute and hour hands, which are driven by friction off the second hand.

The micro motors are not unlike a standard electric motor that you would have in a power drill or other household appliance. They are just on an absolutely tiny scale.

When the hands are supposed to move, the circuit (which sits on top of this assembly) sends a small voltage through to the copper coils, which create a magnetic field and turn the motor.

The 7A28 movements were the first quartz analog chronograph movement in the world and are extremely well built.

You can see a dent on one of the copper coils here, which was done during a previous service. Luckily it has not broken the extremely fine wire which is thinner than a human hair. These are easily the most delicate part of the watch movement.