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Seiko 7s26A balance spring problem


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Dear amazing community of watch enthusiasts, a newbie here, with probably something that is a newbie problem.

So I bought my first 'vintage' watch to tinker with, a Seiko 7s26A diver's watch from around 1996. I have taken it apart, cleaned the components and started to try putting it all back together. So far so good. I oiled and assembled the keyless works, the main train, the barrel and the barrel and train bridge. Of course testing if everything moves freely. All the jewels seemed to be in the right place as when the barrel is turned with a screwdriver (in either direction) all the gears spin up and everything is beautiful. Next I installed the pallet for and the pallet cock (as far as I can tell without damaging the fork), the pallet fork 'jumps' from side to side when prompted, upon turning the barrel everything still works. Once I try and install the balance spring, it does not start spinning. I have took extra care in slotting it in it's place, when installed and blown some air upon it, it turns freely and comes to a stop very quickly. When I apply some pressure to the barrel (now it only turns clockwise) it doesn't rotate very much, but the balance starts turning just fine. On the other hand, the third wheel now suddenly doesn't turn either (when applying a tiny bit of  pressure to turn the third wheel, the balance starts spinning again). 

I have attached an amazingly shot video to demonstrate my problem. 

Also tried taking everything apart, reoiling (the only thing that I have not is the diashock, as I do not want to damage that with my inexperience) and putting everything back together.

If anyone could help me fix this, I would be eternally grateful.




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I would remove the balance and check the pallet fork again. Then let down power and remove the pallet fork and check for any resistance. 

Then reinstall the balance without the fork and check how freely it swings. 

Is the motion works installed? If it is, remove it to eliminate all unnecessary possibilities. 

There is no escaping from working on shock protection jewels. Get a scrap movement and practice on that first.

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The mainspring is actually a new old stock complete barrel (part 201.075) that I had to replace (as in my bravery I managed to break the original mainspring) so I assume there is no problem with that. When the ratchet screw is turned, the click slides in between the teeth of ratchet wheel and a 'winding' sound can be heard. No gear movement the pallet and the balance are installed, when they are taken out, upon winding, the train wheels turn. 


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Hi. Can’t open the vid on the iPad but I assume that when checking the train without the balance and fork in the wheels when run down experienced a little reverse spin (backlash) if so just install the balance, no fork and give it the puff test. It should oscillate for a while under its own tension quite freely 20 secs or there abouts a thing less like a couple of oscillations check the end shake. 

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