Seiko 7s26 problem - need help

[hokavan]

Hi

 

I’m trying to service a Seiko 7s26 and encountered a problem of strange rate as shown in the video

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The rate should be 21600 but it varies from 12000 to 25200 and sometimes could not be detected.

I’v check both pivots of balance wheel. They are in correct position.

Please look into the video and give me advice

 

Thanks

Khoa

[jdm]

8 minutes ago, hokavan said:

I’m trying to service a Seiko 7s26 and encountered a problem of strange rate as shown in the videoThe rate should be 21600 but it varies from 12000 to 25200 and sometimes could not be detected.\I’v check both pivots of balance wheel. They are in correct position.

Problem is not rate but that the balance/escapement is basically not working. It's quite common on the 7S26 which needs every single part to be 100% perfect to produce good amplitude and thus reliable timekeeping. So you have to check again the parts and functions involved, as well end-shake.

Be aware that in some cases the issue cannot be fixed without replacing balance complete and possibly more parts, up to the complete mov.t if the objective is to have a working watch.

[Chopin]

Had a pretty similar issue with such a movement and the hairspring was a bit faulty.

[oldhippy]

Have you demagnetised the balance? Make sure you have used the correct oil on the balance. Never oil the pivots of the pallets. Make sure the impulse pin is clean and smooth (not chipped) and firm in the roller. In other words, go over the pallets and complete balance with a fine tooth combe

[rodabod]

Inspect the hairspring. They are as soft as butter on these watches. 

[hokavan]

On 5/3/2018 at 10:55 PM, jdm said:

Problem is not rate but that the balance/escapement is basically not working

Exactly. By somehow 2nd round of the hairspring is stuck in the curb pin of the regulator. So  it made very strange rate as shown in the video. 

On 5/4/2018 at 8:33 PM, rodabod said:

Inspect the hairspring. They are as soft as butter on these watches. 

That's right way I've gone through. 

Finally I have removed the stuck hairspring from the curb pin. 

Now the problem is the balance wheel stops after a few beats. I've tried to clean the pallet, lever pivot, demagnetized the balance wheel. Nothing works. The balance wheel still stops after 1-2 beats.

Still need some more advice the the case.

 

[hokavan]

On 5/3/2018 at 11:58 PM, oldhippy said:

Have you demagnetised the balance? Make sure you have used the correct oil on the balance. Never oil the pivots of the pallets. Make sure the impulse pin is clean and smooth (not chipped) and firm in the roller. In other words, go over the pallets and complete balance with a fine tooth combe

 

I'm going to clean all parts by ultrasonic. 

I haven't used oil on the pivots of pallet (both upper and lower). For the fine tooth combe, can you suggest alternative way because I dont have the comb

[jdm]

 

37 minutes ago, hokavan said:

For the fine tooth combe, can you suggest alternative way because I dont have the comb

That's just a way to say, inspect everything carefully 

Check that you have the balance end stones (cap jewels)  the right side. Even with a poor HS it should run more than two beats.  But as mentioned above the 7S26 is not the best choice for a beginner, because they can deliver a lot of frustration.

[rodabod]

40 minutes ago, hokavan said:

Finally I have removed the stuck hairspring from the curb pin.

I would inspect the hairspring very closely. Is it flat, and are the coils evenly spaced? Are any of the coils touching the balance arms or anything else?