The inaccurate alignment of the hour counter of an eta 7750

[Floyd0706]

Hallo to all,

today I'm turning to you with the hope of explanation ,why the hour counter of my new Fortis B-42 chronograph is off the markings when counting the hours. I noticed that although the hour counter is aligned perfectly at the zero position, it will misalign when running and counting the hours.

I was wondering if anybody at the forum can help explain the problem.

Thank you all in advance

Frank Schroth

Germany

[Floyd0706]

Here is a picture taken after one hour running.

[jdrichard]

Just needs to be reinstalled to be aligned is my thought???

[Marc]

I have zero experience with chronos so this is just thinking around the problem out loud.

The hour recorder wheel has a jumper that bears on its teeth to hold it in position, and has a reset cam attached to it to zero it. The hand is installed with the reset hammer holding the reset cam in the zero position, so the hand will always correctly reset to zero. If the cam is slightly out of correct register with the teeth on the wheel though then the jumper will hold the wheel slightly out of register with the elapsed hour markers.

Alternatively, if the jumper isn't correctly engaging the teeth then this too could result in misalignment of the hand when running, but correct zeroing when reset.

Like I said I'm speculating here so best to wait until someone with expertise in this field responds.

[Floyd0706]

Thanks guys for your thoughts. Since I don't have any knowledge of watch movements I'll probably take it to my watchmaker and see what he says. Maybe someone with in depth knowledge is answering on my post in near future. Thanks again.

Frank

[jdrichard]

Thanks guys for your thoughts. Since I don't have any knowledge of watch movements I'll probably take it to my watchmaker and see what he says. Maybe someone with in depth knowledge is answering on my post in near future. Thanks again.
Frank

Marc most certainly has in-depth knowledge.


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[Floyd0706]

JDRichard,

and how do I contact Marc?

Frank

[jdrichard]

JDRichard,
and how do I contact Marc?
Frank

I this form.


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[nickelsilver]

The 7750 hour counter is directly geared to a pinion on the barrel. It slips when the chrono isn't engaged, and runs when the chrono is engaged. The thing that keeps it from running is the brake. Early brakes were smooth and held the tips of the teeth of the hour counter wheel; these would slip sometimes so the hour counter would run with the chrono disengaged.

Later brakes are toothed. There's a slight chance that if the chrono is stopped and started the brake might shift the wheel slightly (and the hand). I haven't observed it but it's possible.

What's more likely is the printing on the dial is slightly off. If it zeroes correctly and is off that much at 1 hour, let it go and see where it is 3 and 6 hours later.

[Floyd0706]

@nickelsilver

Thanks for the info! I didn't understand everything due to language barriers(I'm German), but I will check at three hours and then at six  hours!

Frank S.