I recently serviced this very rare Seiko 7c43-6020 Mini Tuna for a customer. This is a nice example despite missing its plastic shroud-- these often fail over the years. The watch looks every-bit a robust and nice looking diver even without the shroud. The watch had been damaged by an incorrect battery. This incorrect battery put pressure back onto the movement, binding the day/date driving wheel and causing it to break. Since folks are now paying a good deal of money for vintage quartz watches, often $1000+, I wanted to point-out some realities with them. Quartz watches need to be serviced like mechanical watches and the cost and time to do it well is comparable to a mechanical watch. The misconception is that they last longer and require less service. The truth is they require more frequent service with battery changes wherein they can easily incur damage such as to their coil or as we see here. I am often asked— why not just swap the movement if it stops working. Dirt or damage inside the movement will cause it to consume the battery faster and/or stop. Swapping the movement with another used one won’t make long-term sense as the replacement will need to be serviced soon even if it runs due to the same dirt, past damage, and lack of lubrication. You can’t just change a circuit, spray some gook inside, or apply a magnetic field to unjam it and get anything but no result, more damage, or a short-term one.