Seagull ST-25 stops for no apparent reason

[Rolexman]

When I first received my IWC 7 day it was DOA. I wound it, shook it but it just didn't start. I saw the Power Reserve indicator move and it indicated full after some shaking and winding. So the barrel wasn't the problem as the tensions of the main spring was transferred to the PR module....When I pulled the crown (hack) and pushed it back in the balance would make some swings and then stop. The second hand never moved an inch. If I repeated this the balance would keep making some gentle swings and stop. Each time the second hand wouldn't move.

So I uncased the movement (greased all the seals while I was at it) and looked if something was jamming. Nope, Balance was free, hacking lever was nicely retracted and the hands didn't touch anything. So I slightly pushed the second hand and miraculously the movement started up. After some hours monitoring I concluded it ran almost a 100% accurate. It didn't loose or gain a second in 12 hours! What a great movement and watch, but my joy was just brief....

10 minutes ago I saw to my great disappointment the movement stopped again. With the same problem as described in the beginning. At first sight it seems the second hand stoppped at the same position as the first time, although it passed that position like a zillion times the last 12 hours

What is wrong with my movement?

[RWG Technical]

As you know it is very difficult to troubleshoot without actually seeing and being able to inspect the movement in person.

Your description is excellent, so I will offer the following:

My guess is that you have a damaged gear, and probably it's the second wheel that is damaged.

If you can, I would do the following testing. Let down the mainspring, meaning unwind the movement fully. Remove the dial and hands to prevent damage. Then remove the balance and the pallet cover and pallet fork. With the stem in place, turn the crown 1 turn and monitor the gears, do they move or are they jammed? This is the only way to diagnose this problem, first you have to make sure that the gear train is free and working as it should, with one turn on the crown, you should get a lot of movement and when it stops spinning, the escape wheel should turn in the opposite direction 1-2 turns. If this is not true, then you have to investigate and fix these problem(s) before moving on.

Forget the balance and anything around it, until you are positive that the motion works is free and not defective.

RG

[andreww]

Is it a stop watch?

[Rolexman]

Thanks for your insight Rob. I know my way around watches but removing the balance and pallet fork is something new for me. It does however looks straight forward. Only 2 screws and one can remove the balance and take out the pallet cover and fork....

Do I first have to make sure the second hand is running again or do I leave it jammed? IMO the train can't be the problem as it ran perfect for 12 hour, can it? The balance want's to move so the train transfers the tension correct. Maybe it's indeed a damaged or gummed up seconds gear in which case isn't it better to inspect this wheel first (don't know how)?

[RWG Technical]

If you haven't removed a pallet and balance before, I strongly suggest you don't risk removal. These two parts are a challenge to re-install, and the balance with it's pivots as small as a hair is so easy to break off.

It could very well be a gear, but with any defect you have to start somewhere. If the hands are not touching, then you have to start with the gear train and make sure it's 100% and then move to the rest of the parts.

Not much else I can offer from this end...maybe a good blow with your dust remover and a detailed exam under the loupe will help isolate the problem.

RG

[Rolexman]

Thanks Rob, I will start with removing the dial, hands and bridge and some close examination with my loupe. Thanks again!