On this page you will find my photo sequences for the disassembly of some common vintage Seiko movements. I can’t say I am doing it in the “correct” order if there is such a thing as I am not a professional just a mere hobbyist. I always start with the calendar side and then move to the movement size afterwards. If you took the movement side apart first you would have difficulty in removing the centre wheel as it is held in place by the cannon pinion. I will be adding more movements as I go along.
Here you can find the official parts list from the 7025 datasheet. Unfortunately I cant find the full service manual
so if you download the 7005A manual this is practically the same movement.
Download here: Seiko 7025A parts List
Here are download links to some useful Service manuals and guides for the 6139. There is no specific guide for the 6139B as the differences in movement are minor.
Seiko 6139A Technical Service Guide: Seiko 6139A Service Guide (In Colour)
Seiko 6139 “Pollys” guide, this helped me on my first attempt: Pollys 6139 Guide
Seiko Official 6138-6139 Repair Manual: https://myretrowatches.com/6138-6139-calibers-repair-manual/