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28k a7750 flaw


andreww

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Just wondering if The Zigmeister or any of our other movement pros could chime in on why this happens...

When the chrono is activated on the 28k 7750, the minute totalizer flips over when the chrono second hand is at about 58 seconds. Not a big deal unless you are timing an event that last 6 minutes and 59 seconds, as your reading would actually be 7 minutes 59 seconds.

Is this some sort of design flaw, and can it be fixed with service? My 21k 7750s function as they should, so it seems like a flaw with the 28ks only.

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It can't be fixed, it's a design issue. The tolerances are in the fractions of a mm for the tab and gears that make up the minute counter, and there is a precise alignment of all the part if you want it to work.

Even with all the parts lined up and adjusted perfectly, the minute counter starts to flip over before 12, nothing can be done to change it...

RG

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It can't be fixed, it's a design issue. The tolerances are in the fractions of a mm for the tab and gears that make up the minute counter, and there is a precise alignment of all the part if you want it to work.

Even with all the parts lined up and adjusted perfectly, the minute counter starts to flip over before 12, nothing can be done to change it...

RG

Thanks Zig, I assume that the ETA version works as it should?

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Yes, the ETA7750 starts to tick over at 12, not before.

If it was adjustable on the Asian 7750 I would modify it, but for some reason they got the alignments of the gears slightly wrong, and because of this and the precise alignment required to get the seconds gear to switch over the minute gear, there is no way to fix it...it's just one of those things we have to live with.

RG

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I've recently read on rwg a member reporting his new a7750 based watch flipped over on 12. Can't remember his name or topic tho.

Better send that one back to the dealer. QC checks failed...it was supposed to be incorrect to differentiate it from a gen Swiss movement. ;)

Interesting question Andrew...I wondered the same thing for the longest time...never thought to question it.

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I've recently read on rwg a member reporting his new a7750 based watch flipped over on 12. Can't remember his name or topic tho.

That may have been me slick. I posted that I received a skyland v3 that flips right at 12:00. The minute totalizer starts to move at about 2-3 seconds before 12 and "snaps" to the next minute right at 12:00. I am sure it is the 28.8k movement.

I would like to send it to The Zigmeister for servicing, but I'm afraid that a cleaning will fix this "flaw" and it will advance a couple seconds before 12:00 like all my other a7750s. :D

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The Grand Carrera is 21.6K with regulator.

My C1....which is a 28.8K with regulator (this is the new modified movement being used on some reps)....ticks over exactly @ 12....I think I mentioned this in my initial review of the watch as well. Most or all of my 7750x28.8K....move around 58 sec.

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The Grand Carrera is 21.6K with regulator.

My C1....which is a 28.8K with regulator (this is the new modified movement being used on some reps)....ticks over exactly @ 12....I think I mentioned this in my initial review of the watch as well. Most or all of my 7750x28.8K....move aroun 58 sec.

Thats what I was thinking, that it was a Grand Carrera. Mystery solved. I am aware of the 28k with regulator, but those are new and not in that many watches. Hopefully it will become the standard movement for our reps!

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It can't be fixed, it's a design issue. The tolerances are in the fractions of a mm for the tab and gears that make up the minute counter, and there is a precise alignment of all the part if you want it to work.

Even with all the parts lined up and adjusted perfectly, the minute counter starts to flip over before 12, nothing can be done to change it...

RG

Is this the same reason why starting the chrono will first cause the chronosecs to jump back a little before it starts counting? The ETAs seems to start immediatly from 0.

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Is this the same reason why starting the chrono will first cause the chronosecs to jump back a little before it starts counting? The ETAs seems to start immediatly from 0.

Not really...from the stopped position, the hammer is holding the seconds gear fixed in place, when you press the button to start the chrono, the hammer releases, and at the same time the tilting pinion engages into the center seconds gear. If your tilting pinion isn't adjusted correctly, there could be a slight movement of the seconds gear before the tilting pinion engages.

Remember that the seconds gear is free to spin around, it is only stopped by a brake lever, the reset hammer, or the tilting pinion, anytime you switch modes, one of these has to disengage and the other engage to prevent the hand from moving, any slight misadjustment between any of these 3 items and the hand can swing freely.

RG

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Is there any way to tell if it's a 28k8 or 21k6 ? I can make some pictures if needed. Since i am a newbee i have no idea what C1 is...

The easiest way is starting the cronograph and counting the ticks of the second hand between two minute markers. Three ticks = 21600; four ticks= 28800.

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  • 2 months later...

Now that's interesting. My SMP Chrono also has this flaw, the chrono minute hand starts to tick over at 58 seconds and jumps to the next minute at 59 seconds. This sort of annoys me. I have learned from this thread that this is indeed a design flaw. Can't the responsive (poorly made) parts/gears simply be exchanged by their respective genuine ETA counterparts? If so, what are they?

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