Replacement of a 7750 or other solutions

[Nono92]

Hello,
What would you advise in order to make a 7750 sec@12 more reliable ? Using a DD MODULE with a basic movement seems difficult to make and expensive... Is there another solution to make it as reliable as the gen with 3120 (it's for an AP ROO chrono) ? Thanks for help. Regards.

 

[ado213]

Unfortunately there are no alternatives on reliability, apart form the DD module and base movement. All AP Roo chronos with 7750 suffer the same issues of movement degradation over time. In short the A7750 and in fact the Swiss 7750 are juts not designed to drive an additional train to move the running seconds

whereas the DD module and 2892 movement marry together seamlessly, with the DD module being designed to accommodate the output power of the base movement and the running second hand being driven directly off the movement 4th wheel

Some of the older 7750's did not have a jewelled centre wheel, which does reduce friction from the transfer train, the new 7750's do have this additional jewel and fair better. If yours doesn't have this centre wheel jewel (on the Hour wheel) adding it would be an upgrade. There are five additional transfer gears in an AP Roo 7750 movement, each one saps and amount of power from the base movement causing amplitude drop and variable time keeping.

In addition these transfer gears all carry an amount of "backlash" within them, this "backlash" can cause issue on the running second hand, making it jittery. There is a very small brass compression washer on the running second pinion, this itself can cause issues with amplitude. Too much tension can make it drop, too little and the second hand will be jittery

Heights and settings of these four gears are very critical to the smooth running of the movement. If you service one of these its very important that the base 7750 movement is running perfectly with good amplitude Min (300 degrees) before adding the transfer gears. Add then one by one and run for at least a day to see if they affect the running of the watch. Keep adding one by one and running and you will eventually find the one that is causing you the issue as amplitude will drop. It is important that you run for at least a day when adding the gears, as amplitude degeneration usually occurs over time

The minute counter is rarely an issue, which has three transfer gears and the hour counter is driven directly, so your issues will be the running second transfer gears

So in short the DD module and base movement whilst on the face of it is an expensive option, in terms of longevity its you best option

 

[Nono92]

Hi,
Thanks a lot for these clear explanations ! I read it was impossible to make the replacement without a gen dial... Maybe I am wrong but the positions of the subdial hands might not be at the same place in the DD module and in the rep dial... If I could make a replacement only by buying the DD module and the 2892, it would be great Gen parts are very expensive unfortunately !
Regards.

 

[ado213]

You are correct, with a gen DD module and base movement a gen dial would need to be used as there is a slight difference in the subdial positions

 

[ross29]

Sorry to highjack this thread.

I just got a used ARF daytona and may need a service or replacement. I've looked around but can't seem to find anyone who works on the A7750 movement these carry. I would take it to a watchmaker, but not sure since it has been modified or slimmed as I understand it. I thought of just getting another movement to replace but I figured it's more complicated with the modified "slimmed" movement. Any help or suggestions would be much appreciated

 

[Nono92]

Désolé de détourner ce fil.

Je viens de recevoir un Daytona ARF d'occasion et j'ai peut-être besoin d'un service ou d'un remplacement. J'ai regardé autour de moi mais je n'arrive pas à trouver quelqu'un qui travaille sur le mouvement A7750 qu'ils transportent. Je l'emmènerais chez un horloger, mais pas sûr car il a été modifié ou aminci si je comprends bien. J'ai pensé à remplacer simplement un autre mouvement, mais j'ai pensé que c'était plus compliqué avec le mouvement "aminci" modifié. Toute aide ou suggestion serait très appréciée

I thought the ARF Daytona wasn't a functional chrono. But it needs a 7750 to run the second @ 6 ?

 

[ross29]

Yes, that's the problem. It has the non functioning chronos so a simple swap wouldn't fit I imagined. I guess that was part of my issue. I am hoping to fond someone who is able to work on this or possibly swap it out if needed. Just not sure how to go about it. It seems most don't want to deal with them.

 

[ado213]

The ARF is indeed not a fully functional 7750 chrono. This model can be serviced, the slimming of the case has no bearing on the movement within.

 

[ross29]

Thank you. Now I just have to find someone who is able to service this.

Any suggestions are greatly appreciated.

 

[Nono92]

You are correct, with a gen DD module and base movement a gen dial would need to be used as there is a slight difference in the subdial positions

Hello,
I did some research about the DD module and I found the DD 293. The positions given by DD below are exactly these of the JF rep dial.

What is your impression ? Thank you.

 

[Nono92]

@ado213 It's better now :

 

[ado213]

I haven't measured the JF rep dial, so can't really comment on its dimensions. Just off memory, it would also be worth checking the chrono pusher positions on the case tie up with the 293 module. I seem to remember having to adapt the movement spacer on some of the older cases

 

[Nono92]

I measured the angle between the pushers on the gen (67°) and on the rep (64°). I don't know if it is reliable because the 64° should correspond to the gen (if they use the DD293). But there is no reason to have something different because the DD 2000 had also an angle of 64°... The LWO 283 seems to be a former movement with a misalignement between the pushers and the crown.
If the positions of the rep subdials were correct, would there be another problem with the date wheel or could it be fixed by setting the rep datewheel on the new movement ?
Here it is a photo of the gen AP :