Chronograph time setting. What am I doing wrong?

[P4GTR]

My two A7750's keep extremely accurate time, one of which, serviced by The Zigmeister. A peculiar thing I've noticed with the minute hand specifically on all chrono's has lead me to believe i'm doing something wrong. When I set the time, the minute hand seems to take a minute or two to engage. For instance, I set my Skyland this morning, and checked it many hours later now at 11PM, its accurate down to the exact second, however the minute hand is two minutes behind! It's not losing time so much as its taking time for the minute hand to engage after I set the time.

What am I doing wrong?

[Jkay]

Scary! I hope you figure this out.

[freddy333]

A7750s are notorious for having a bit of 'play' in their works. This translates to an inability to set the minute hand exactly (once set, if you shake the watch, the hand may shift a minute or 2). Some fine that (assuming the movement is properly serviced) if you move the minute hand several minutes past the point you want to set it to & then move it back (counter-clockwise) to set it, you will minimize the deviation. This works in some cases, but I have also seen the opposite to work (move hand backwards past the point & then moving it forward (clockwise) to set it).

[P4GTR]

I've been doing exactly that Freddy, with mixed results. The problem is i've used two different watches to hypothesize. I knew it was not my two chrono's being out of whack, but me not knowing those little intricacies.

I'm going to set the Skyland right now and report back. The watch is less than a year old, kept great time prior, but is fresh back from a The Zigmeister overhaul. A worthy test subject.

Here go's the-

"move the minute hand several minutes past the point you want to set it to & then move it back (counter-clockwise) to set it, you will minimize the deviation.

At 12:27pm I moved it way past, than set it to 12:30... and plunged the crown. We'll see how it go's tomorrow morning.

[cougaree]

I don't have any issues with my Skylands, but I do have the similar issue with one of my BCEs. I'm going to give it a try tonight too. Hopefully this will do the trick.

[RWG Technical]

Freddy has got it right.

The reason for this (and it's common on the ETA's as well) is due to the offset cannon pinion location. In most movements the cannon pinion, which carries the minute hand, is attached directly to the center wheel pinion, when the center wheel moves so do the cannon and the minute hand. This is not the case on the 7750.

On the 7750, the center wheel is not actually in the center, it's off to one side. To the center wheel is attached the cannon pinion gear, this gear drives the minute wheel, which in turn drives the gear that the minute hand attaches to.

So instead of direct drive for the minute hand, you now have 3 gears between the driving gear, and the hand, which means there is slack and therefore play.

I have had success with setting the time backwards to take up the slack.

Just remember that everytime you set the time, you are ever so slightly wearing out the cannon gear clutch, on all watches, not only the 7750, so do it as little as possible.

[lhooq]

Excellent explanations. I have the same issue with my DW 6263, in that I have to set the time 110 seconds in advance!

On my other 7750-powered rep (an IWC GST), no delay whatsoever.

[P4GTR]

Freddy has got it right.

The reason for this (and it's common on the ETA's as well) is due to the offset cannon pinion location. In most movements the cannon pinion, which carries the minute hand, is attached directly to the center wheel pinion, when the center wheel moves so do the cannon and the minute hand. This is not the case on the 7750.

On the 7750, the center wheel is not actually in the center, it's off to one side. To the center wheel is attached the cannon pinion gear, this gear drives the minute wheel, which in turn drives the gear that the minute hand attaches to.

So instead of direct drive for the minute hand, you now have 3 gears between the driving gear, and the hand, which means there is slack and therefore play.

I have had success with setting the time backwards to take up the slack.

Just remember that everytime you set the time, you are ever so slightly wearing out the cannon gear clutch, on all watches, not only the 7750, so do it as little as possible.

This is the guy I trusted one of my favorite pieces to, and he did an incredible job of course. Thanks for chiming in my friend, nice to E-see you!

Look at this lume work... She's looking good, fellas.

Freddy, thank you sir, I believe you nailed it. Here we are about 12 hours later, the trick worked, however the watch is about 30 seconds fast.

-If it is gaining a bit since service, should I (being familiar enough with doing so) use the micro adjust index (#1 in diag.) accordingly? Zig, maybe you are familiar with this individual piece enough to tell me how accurate it was for you, and where to go at this point.

As far as wearing out the clutch, that raises another interesting question. For a watch that is in rotation maybe once a week, is it better, longevity wise, to keep it on a winder, or let it die and reset it? Also, I am correct in that you should swirl the 7750's to start them, no turn or two on the crown to put a little reserve in it?

[RWG Technical]

-If it is gaining a bit since service, should I (being familiar enough with doing so) use the micro adjust index (#1 in diag.) accordingly? Zig, maybe you are familiar with this individual piece enough to tell me how accurate it was for you, and where to go at this point.

After servicing, all movements are adjusted to +6 to +8 seconds a day on the analyzer. This setting is the one that typically produces accurate timekeeping while being worn, the problem of course is that not everyone wears their watches the same way, not everyone moves enough while wearing the watch to have it fully wound, different temperatures are encountered while wearing the watch, and if that wasn't enough, the factory specs on the A7750 are probably no better than + - 30 seconds or more a day...so while 30 seconds sounds bad, it's actually within the design specs of the movement.

A partially wound movement will run fast, so this may be the cause. You can always handwind it carefully and slowly 25+ turns and see if the rate improves, this will confirm partial winding while being worn.

The key is consistancy in the rate, in other words does the watch run 30 fast each and every day it's being worn, if this is true, then slowing it down by the 30 seconds should solve the problem. It is very normal for a watch to gain, and loose, or run even, during different times of the day. The only true test is to adjust the time to an atomic standard, check it 24 hours later, and see what you get, do this a few times and if your getting the same readings, make the fine adjustment. Without an analyzer it's hard to know how much to move the adjuster, so it's hit and miss.

As far as wearing out the clutch, that raises another interesting question. For a watch that is in rotation maybe once a week, is it better, longevity wise, to keep it on a winder, or let it die and reset it? Also, I am correct in that you should swirl the 7750's to start them, no turn or two on the crown to put a little reserve in it?

A regularly serviced movement shouldn't wear out, since the pivots are turning in a film of oil. If the movement is serviced, then I would say the winder is a good choice, but it most likely won't keep accurate time on the winder, your wrist is not a winder, and vice versa. If you don't want it running all the time, you could always hack it at the time you normally switch watches, say every morning, that way you don't have to move the hands a lot to get it synchronized when you put it back on, leaving it hacked won't hurt anything.

As for start up, a few slow easy turns of the crown to give it a charge and then wear it, being uni-directional winding, it takes a lot of wrist movement to keep it charged, most times the rotor spins the other way instead of winding it.

Lume looks great, good picture quality.

[drolson]

I´ve had the same "problem" with my gen Pam 90. When setting the time i always wind one hour in advance an then wind back to the exact time. That solved the problem for me.

Edited August 23, 2010 by drolson

[P4GTR]

After servicing, all movements are adjusted to +6 to +8 seconds a day on the analyzer. This setting is the one that typically produces accurate timekeeping while being worn, the problem of course is that not everyone wears their watches the same way, not everyone moves enough while wearing the watch to have it fully wound, different temperatures are encountered while wearing the watch, and if that wasn't enough, the factory specs on the A7750 are probably no better than + - 30 seconds or more a day...so while 30 seconds sounds bad, it's actually within the design specs of the movement.

A partially wound movement will run fast, so this may be the cause. You can always handwind it carefully and slowly 25+ turns and see if the rate improves, this will confirm partial winding while being worn.

The key is consistancy in the rate, in other words does the watch run 30 fast each and every day it's being worn, if this is true, then slowing it down by the 30 seconds should solve the problem. It is very normal for a watch to gain, and loose, or run even, during different times of the day. The only true test is to adjust the time to an atomic standard, check it 24 hours later, and see what you get, do this a few times and if your getting the same readings, make the fine adjustment. Without an analyzer it's hard to know how much to move the adjuster, so it's hit and miss.

A regularly serviced movement shouldn't wear out, since the pivots are turning in a film of oil. If the movement is serviced, then I would say the winder is a good choice, but it most likely won't keep accurate time on the winder, your wrist is not a winder, and vice versa. If you don't want it running all the time, you could always hack it at the time you normally switch watches, say every morning, that way you don't have to move the hands a lot to get it synchronized when you put it back on, leaving it hacked won't hurt anything.

As for start up, a few slow easy turns of the crown to give it a charge and then wear it, being uni-directional winding, it takes a lot of wrist movement to keep it charged, most times the rotor spins the other way instead of winding it.

Lume looks great, good picture quality.

That explains a lot. It was minimally wound, so that could explain the deviation. This has been very informative, cleared up many questions. Also, I never thought about hacking it. Thank you for the teachings, Z.

[Bike Mike]

I find Z's posts more and more interesting now that I have been working on watches for some time. Not to say they were not interesting before...just when he describes some functionality, I can picture in my head exactly what is going on...like the offset cannon pinion on the 7750.

[RWG Technical]

That explains a lot. It was minimally wound, so that could explain the deviation. This has been very informative, cleared up many questions. Also, I never thought about hacking it. Thank you for the teachings, Z.

Your welcome, hoepefully it makes sense...

Isn't that a children's song "...old Macdonald had a farm...with a Hack Hack here, and a Hack Hack there..." he must have had a 7750 as well...

[cougaree]

hahahahaha, R, you are a funny man! Can't wait to choreograph your song.

[P4GTR]

Your welcome, hoepefully it makes sense...

Isn't that a children's song "...old Macdonald had a farm...with a Hack Hack here, and a Hack Hack there..." he must have had a 7750 as well...

It makes perfect sense. Your joke however.. I don't think its going to make the cut, it doesn't quite hack it!