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greg_r

User guide to the A7750 movement.

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greg_r   

The 7750 is probably the most-discussed movement on the rep boards. Partly because of the notorious issues with the secs@6 movements, but also because it has built a reputation for being less reliable than other movements. The reliability issue is, however, largely based on early samples of the low-beat version - the movement currently being fitted to replica watches is quite a bit more reliable than has been the case in the past - although problems can still occur.

 

Note that the standard configuration for the A7750 is with the seconds subdial@9. Many reps have modifications to move this to 6, 12 or 3. In all instances the extra gearing required to do this adds extra drag to the movement and impacts reliability, but the secs@6 modification is the most notorious as it's not well executed (no extra jewels have been added) and the failure rate is significantly higher than other variants.

 

Here are a few basic guidelines - culled from posts by Ziggy and various other folks who know a damn sight more about this movement than I do wink.png .

 

1. If you have to hand-wind the movement, do so gently and try not to do it too often. The hand wind mechanism is quite high-geared and there is a danger that you can strip the gears if you're too rough with it. Best advice is to start the watch with a quick 'swirl' then just strap it on and wear it. Normal use should keep it wound (I can vouch for this as it's what I do.).

 

2. Yes, the 7750 rotor is usually that noisy wink.png

The 7750 rotor only winds in one direction. The winding direction has resistance since the rotor is trying to wind the mainspring. In the other direction there is no resistance at all, and the rotor is free to spin. If the rotor bearings are dry, there is nothing preventing the rotor from spinning like crazy. Lubricating the bearings helps to quieten the rotor a bit and prevent such a free spin in the non-winding direction.

 

3. Don’t set the date between 7 pm and 2 am

This is true for all 7750’s, Asian or gen Valjoux. Note that this is also good practice when setting the date on other movements. The date gear starts to engage with the date wheel around 7pm and disengages totally by 2 am, if you attempt to do a quick date change during the engagement, you may damage the watch. Best advice - with any watch, whatever the movement - is to wind the hands forward past midnight until the date changes, then with the hands set to around 6am, use the quick set function to change the date as needed.

 

4. Don’t re-set the chrono with the seconds hand anywhere but between 10 and 2 on the dial.

The reset hammer can slam down very hard onto the heart cams for the seconds and minute counters. This force can cause the seconds hand to slip if the hand is sitting anywhere but between 10 and 2. Even genuine watches can suffer from this problem. A slipping center seconds hand is totally preventable by the owner, all you have to do is make sure you never reset your chrono between anything but 10-2. In addition, DO NOT push the chrono reset pusher (@ 4) while the chrono hand is running. It is also recommended that you resist the temptation to 'play' with the chronos too often - especially on an unserviced movement - as this can increase the chances of problems.

 

As I said - this post has been collected from comments by various experts on the boards. If more knowledgeable folks than myself have any corrections or observations, do please feel free to comment and I'll correct this post if appropriate. Thanks.

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GC   

one addition:

Do NOT push the chrono reset pusher (@ 4 o'clock) while the chrono is running!

First stop the chrono by pushing the start/stop button (@ 2 o'clock) than push the reset button.

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graman   

Great post Greg! :thumbsup2:

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Luthier   
And when you receive a new watch, never forget to check if all the screws are well screwed....

 

Right.

Screw the screws first.

:lol:

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Rav747   

Question, I have a 7750 and i have noticed that even if i wear it for a whole day, remove it by night, by the next morning its dead. I thought 7750s have decent reserves. I dont even use the chronos. Anything i can do? or is it a lemon? Other than that, as long as its on my wrist it keeps great time.

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Have you tried giving it a good charge via manual winding? Wind it up 30-40 times and see how long the charge lasts. (Wind slowly, though.) Sometimes, when new, they just need a full charge before they'll wind well on the wrist.

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Rav747   
Have you tried giving it a good charge via manual winding? Wind it up 30-40 times and see how long the charge lasts. (Wind slowly, though.) Sometimes, when new, they just need a full charge before they'll wind well on the wrist.

 

Thanks, Doc. No i haven't. At most, i have given it maybe 10 full winds really slow. So, wind it 30-40 times slowly, shake gently to start it up? Dumb question, but by winding you mean the crown, correct? Its a blacksteel by the way.

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Yes, the crown. After winding that much you shouldn't have to shake it to get it going.

 

If it still doesn't hold a charge for long, I think it's an easy fix. (Someone else will have to help with that, though. :P)

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Rav747   
Yes, the crown. After winding that much you shouldn't have to shake it to get it going.

 

If it still doesn't hold a charge for long, I think it's an easy fix. (Someone else will have to help with that, though. :P)

 

No problem. Thank you.

 

Just did it. lets hope it works.

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warcelo   

Question:

 

If i push the chrono reset pusher while the chrono is running it dies instantantly or only after lots of wrong pushes? Is that the same with the date?

 

Thanks!

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onzenuub   
Question:

 

If i push the chrono reset pusher while the chrono is running it dies instantantly or only after lots of wrong pushes? Is that the same with the date?

 

Thanks!

 

 

 

Why would you do this?

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warcelo   

I woulden´t but if someone who dosen´t know anything about watches get it to take a look and press it wrong for example.

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debian   

I took the case back of my PO Chrono to try to figure out what could happen if pushing the reset while running.... because I'm a little nervous about that sometimes.

 

For my untrained eye it seem like nothing at all can happen. but I don't dare to try :D

It looks like the flipping thing the reset pusher is pushing when resetting goes to a position that it can not reach when the chrono is running. and when stopping the chrono the flipping thing goes to a position that the reset pusher can reach and when pushed it reset the chrono....

 

When the chrono is not running the reset flipping ting is also in a position that the pusher can not reach.

 

I realize now trying to explain that i should have taken pictures to help describe.....

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warcelo   

That´s really good to hear! I was afraid of letting friends "play" with it mess up the movement. Pictures would be awesome!

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debian   
That´s really good to hear! I was afraid of letting friends "play" with it mess up the movement. Pictures would be awesome!

 

But you shuld not listen to me... :D

I'm just a noob trying to figure out how these thing works. apparently it's not recommended to reset while running. you here that all the time.. but It bugs me a bit that I don't know what happens when pushing the reset while running.

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debian   

DSC_0048.jpg

Chrono completely stopped

 

DSC_0049.jpg

Chrono completely stopped, chrono reset button pushed

 

DSC_0050.jpg

Chrono running, if pushing reset button, the flipping thing is not able to touch anything.

 

DSC_0051.jpg

Chrono stopped, if pushing the reset button the flipping thing will push something and reset the chrono.

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warcelo   

I pressed it many times looking at the movement, nothing happens.

Debian you´re right, the flipping thing is not able to touch anything. It's safe t do it IF YOU HAVE THE NEWER 7750 model! I dunno about the older models!

Edited by warcelo

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