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Improving the reliability of AP seconds at 12 movement

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A member of the forum sent me two APs with seconds at 12 that stopped working. After reading so many problems about this movement I was really interested in finding out why they are having so many troubles.

The review of the movement showed that was not perfect, but not as bad as failure reports prove. BTW, the review is here:

A couple of pictures of the APs, they only run for a couple of minutes:



To fully understand why they are stopping working, we show here briefly the modification OF THE SECONDS. Minutes modification is not problematic.

Following picture shows the natural output of seconds in the 7750 movement. In position 9, red circle. The modification moves the output to position 12 o’clock.


To do that, the Chinese worker fits on this output the gear A:


Gear A engages to gear B:


And gear B engages to gear C, which “moves up” the rotation to the top plate. Where connects to gear C. Finally, gear E is the output of the AP movement:


The obvious problem of the modification is that gear C is sliding over the plate, and E has no a jewels in the bottom position. The rest of the modification is well done (jewels up and down).


I have found out why AP@12 stops running in short or medium term. For example, the two APs showed before had the problems that will be illustrated now. It is an assembling problem, wrong assembling.

The gear A is wrongly assembled. As a consequence, gear A is not engaging correctly to gear B. Following picture shows how the teeth of the gears are interweaved, stopping the watch.


Gear A is under gear B, they are not gearing correctly, and the watch stops. After shaking, watch may run again.


To be honest, assembling gear A is not easy. Solution is removing gear A and assembling it correctly, at the same height as gear B. This is very delicate. You can break the natural output of seconds when removing gear A, and it is not easy to assembly it correctly. In addition, gear A has to be perfectly flat. Here is well assembled:


Following video shows how bad is running the connexion gears A-B , just as it was assembled in the factory:

Just check how gear B rotates, but pushed from THE BOTTOM by gear A. They are not well engaged. In some moment, the teeth may be interweaved, and the watch will stop. Now it is possible to understand the members complaining about their AP@12, that only last for a couple of days.

Following video shows gears A and B, when the position of gear A has been corrected.

Running is now correct. Although gear B is not running very smoothly (tolerance problem). However, the final movement at gear E is quite smoother. This video was taken when only gears A and B were working.

Therefore, the first task when inspecting AP@12 movement is checking the position of gear A


The movement has two points that may reduce its long term reliability. Gear C, sliding over the plate, and gear E, that lacks a jewel. Let us improve the situation.

Improving gear E.

Let us remember where gear E is:


Red arrow in following picture shows the surface we are going to polish:


Polishing the surface will reduce friction, as plate surface is quite rough. We are helping the movement to rotate all the gears of the modification:





Improving gear C

Follows some pictures of gear C, and its two faces:


Upper face:


Lower face:


It is sown that lower face, face that is sliding over the plate, is flat and rough. Upper face has a slot, to reduce contact surface with upper plate. However, the plate where gear C is rotating has a protuberance to reduce contact surface.

Now we are making a slot on lower face of gear C. The main objective is reducing moment of inertia of this gear, helping the movement to need less power to rotate this gear.

As seen in following picture, gear C is quite tall, and made of steel…it is very heavy.


Making this slot is important, therefore, to reduce mass. In addition, second video showed that movement in gear B is not smooth. Therefore, reducing moment of inertia is important.

Hence, gear C s going to be turned. Diameter of gear C is a bit more than 5.3 mm. Two option for fastening this gear in the lathe. Left, common collet. Right, step collet. I chose right option, better for turning a slot. It requires less pressure, better for not damaging the teeth of the gear.


Gear C is turned:



The slot is finished:


A better picture of the new slot:


Now it is time of polishing gear C, to reduce friction as well. For polishing I made a base of epoxy resin;


Polishing the gear (both faces):


It needs a good cleaning, last step of cleaning, using gasoline:


Gear polished and ready to be assembled:


Now, after these steps shown in this tuto, we have increased a lot the reliability of AP@12 movement. Both watches have been tested extensively…running very well.


*Have you applied graphite?

No, graphite is not a long term solution.

*Have you consider swapping an ETA 7750 movement?

Asian 7750 can do correctly the job. And an ETA movement, with gear A assembled wrongly, will have reliability problems.

*Is it necessary to service the movement?

It is always a good option. However, the most important here is to tae care of the modification

*What about Portuguese and Daytona?

They are very bad designed, a lot worse than AP@12. Just avoid that watches. However, I think we have wrongly diagnosed the problems of these movements. Friction may not be the only reason of malfunctioning.



Edited by Francisco
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*What about Portuguese and Daytona?

They are very bad designed, a lot worse than AP@12. Just avoid that watches. However, I think we have wrongly diagnosed the problems of these movements. Friction may not be the only reason of malfunctioning.

:thumbsupsmileyanim: :thumbsupsmileyanim: :thumbsupsmileyanim: :thumbsupsmileyanim: :thumbsupsmileyanim: :thumbsupsmileyanim:

Thank you very much Francisco!

It is a pleasure to read your work

Excellent work and excellent suggestions

All the best


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WOW...very good information and understandable for everyone.

Hope the factories would notice your review and have these gear-issues fixt....albeit that would reduce some of your service-works (just joking).

Thx a lot, I think I need to send my beloved ROO

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As usual, great work Francisco.

I have a question. With those gears on plate mods, how hard it would be to install jewels there?

installing a jewels is possible. However requires a lot of precision. if not, movement will not work correctly.



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Hi Francisco,

I am very new here, and I own a couple of AP rep (A-7750) with running seconds at 12 o'clock, with the standard problems. the watch just does not run smooth at all, and stops often.

I understand that you could modify the movement to provide better reliability. I have a few questions:

1. Would you accept the tasks of upgrading the movements of both my AP?

2. How much would it cost me please, if so, and how could I pay you?

3. Would you be able to return my watches to Singapore after repair?

I am not a time waster, please do not worry. I am a genuine AP fan who is very frustrated with the movement of the reps. I am finding someone who could help me, and after reading your columns, it seems to me, kind sir, that you are the best man for the jobs.. do get in touch with me thank you!

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