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Valjoux 7750 Movement


chronomike
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Please excuse me if I am way off topic, but I couldn't think of a better topic to place my question!

My concern is about a Hamilton Navy Frogman, using a Valjoux 7750.

As I was trying the watch at the shop, I wanted to get the feeling of the date - time setting mechanism. Since I know that there is a certain period during which the date should not be changed, I moved the hands past 03:00 am. While trying to (gently) set the date, I felt a slight resistance, probably indicating that the date gear train was still coupled with that of the timekeeping. I, then, advanced the time even further, maybe past 05:00, made another attempt, managed to advance the date dy 1, then felt resistance once more. I finally advanced the time past 6 or 7 am, and from then on, no problem.

I own the watch for 5 days now, the date has been changing fine, save for one thing: it changes from 12:00 am to 01:00 am. From my experience so far, the date usually changes prior to, or around 12:00.

And, finally, my question: is it possible that I damaged the date change mechanism? Is it possible to alter the change point of the date, after applying gentle force on the gear train while coupled to the timekeeping one? Could this be the reason why the date changes around 01:00 am in my watch, or is this normal?

Is there a way to know that the date change mechanism works fine, or alternatively, what are the symptoms of it malfunctioning?

Please excuse my long post, but more importantly please excuse me if I wrote utter garbage, due to lack of technical background on watchmaking!

Cheers!

george.

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on the 7750 you should always set the hands to around 12:00 NOON before changing the quick set date.

In fact this is good advice for any quick set date mechanisim.

The date change mechanisim is linked to the hour wheel so if it's not showing the right time when the date is changing over it's not a fault with the mechanisim but more a case of the hour hand has been put on the pinnion out of sync.

(A mistake I've made a few times :ph34r: )

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the hands need resetting ,the hands are taken off the watch and set correctly to the date change,i.e as the date changes the hands are set at 11.55.

Thank you Pugster for your response!

As I understand it, what you suggest will shift the date change time.

What I want to know, actually is the following:

Is it possible that the watch was originally set to change the date at, say 11:55pm as you write, and my handling caused the shift ACCIDENTALLY, afterwards? Is it technically possible to case a shift of the date change point as a result of a strain, however subtle, on the mechanism?

Once again, thanks for your greatly appreciated feedback!

george.

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im not sure if your rough handling might do it ,i only strip basic movements (change chrono levers etc) , i wouldnt totally strip a mechanical chrono at the moment as im not experienced enough (would end up with losta bits left over :D ) ,someone else here who is advanced enough to strip/ressamble a mechanical chrono should be able to tell you tho, the only thing i can think of is if the hr hand was abit loose on the pinion and it got caught/slipped at some point.

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How well are the hour and minute hands lining up? Are they spot-on together at 12? I would think that would be the first indication whether or not the hour hand slipped somehow. I they are good, I would not mess with it. You go to sleep, you wake up, the date has changed. You dont know, it might change as soon as you fall asleep, or just when it realises that you are waking up! :P

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I agree with Marius; if you can live with it changing between 12 midnight and 1 a.m. I would leave it till the watch is due a service. If it is really bothering you a local watchmaker could fix it in a few minutes by repositioning the hour hand.

Have you damaged the date mechanism? Probably not in my opinion; with my 7750s I always changed the quickset between 9am and 3pm for the reasons you point out.

Nice watch by the way, I have been thinking about getting the one without the metal crystal protector, have you got any pictures?

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