THE ASIAN SECONDS AT 6.00

[RolexAddict 1]

 

The seconds at 6.00 gear train, The conclusion.

My own theory:

I could be wrong, but I try to reason as a Cartesian and with logic. Since I have disassembled the first plate under the dial, observed these 4 gears moving, touch and remove all, I am not convicted of the drag or what else. When I put back the plate, screwed back the 3 screws holding this plate, evrything sounds like well assembled, nothing who remains my attention... except the little bit of play between these 4 wheels and this makes me think about the jerky seconds hand.

Again, I could be wrong, I am not a professional.

Reviews from varied boards about the oiling or graphite coating this gear train retained my attention. Even if I'm not convicted, I admit that anyway, put grease, oil or graphite on these gears, will not affect anything and can only be good.

The problem is the disassembling. Its not so easy like on a ETA, to remove the hands and dial. Also re-stack every thing at the right position especially the chrono hand. Hours and minutes hands are big and thick but the black line in the middle is made from water paint, the sub-dial hands are stacked very tight, they need to be removed with a appropriate hands remover made for chrono hands to avoid to brake the gears hand axes. It happened to me, and not the first time, more time later. But fortunatly, these are generic gears, and I have a "magic box" with lot of various gears picked out from old crap chinese movements...

So the gear train graphite coating job is not so easy. I forgot: the dial is hard to remove as the hooks holding the tenons are inverted when locked and the assembly is very tight.

I will make my conclusion on this chapter with pics and comments, and again new pics who confirm there are not 11 gears causing drag.

 

Here from letf to right: the dial, the removed first plate under the dial and what you see is the so mystic gear train...

 

Then the 4 little gears from the seconds at 6.00 gear train are removed and the second plate unscrewed. On the right you can see the primary gear module. This one support the movement second gear and the hours sud-dial reset device.

 

We end with a zoomed pic from this primary plate: Just remember the view is from the dial side, so nothing is inverted, the crown is on the right side, start/stop chrono pusher on the top and the reset on the bottom at 4 o'clock.

1) The minutes counter/reset gear

2) The movement seconds gear

3) The hours counter/reset gear

4) the reset levers/sping/bellcrank device, I f you disassenmble a A7750, all these pics will be helpful for the re-assembling...

Also note, there are lot of drilled holes and empty designed notches as this background movement plate is used for a lot of sub-dial configurations and also day/date features.

 

ENTERING THE WORLD OF THE A7750 CHRONO MODULE (THE CASE BACK FACE)

 

 

OVERVIEW

 

Now, for all following comments, you need to figure the case is inverted. The start/stop pusher is at the bottom.

The reset pusher is on the top.

Huh.... This is what you see when you have removed the rotor. Looks complicated ? Not simple, o.k, but easy to understand how it works.

 

First, the pusher levers. Remember, the case is inverted.

In red, the start/stop system. In green, the reset system. Yellow circled, the "mixer" or "distributor" I don't know how else to call it.

 

The same pic who shows the chrono start/stop system: the bellcrank spring and his adjustement screw. The bellcrank is under the removed cover plate. Circled in red, the movement minute to chrono hand transmission. The hole is in fact a servicing hole.

 

Now the first cover of the chrono module is removed, so you can see the bellcrank. The spring is a clone I made, the original jumped again on the carpet when I removed the plate.

 

 

A zoom on the transmission system, now this is what I suppose to be (probably) the jerky seconds at 6.00 hand and probably also why the watch stops to run.

 

The 5 parts necessary to start, stop and reset the chrono hand and the minutes sub-dial counter. The hours hand sub-dial reset levers are under the movement,on the dial side.

1) The reset lever spring

2) The reset articulated arm

3) The chrono hand start/stop bellcrank

4) The transmiter stem

5) The bell crank spring

 

THE SUPPOSED REASONS OF THE JERKY SECONDS HAND

I precise, the following theory and cure for this problem, are probably not the absolute verdict. But I had this on one of my Daytonas, and my prescription and intervention was 100% positive. One of my Daytona died after a few days, another one has the jerky seconds hand symptom, and my diagnostic was good. Both watches run perfect again right now. They also like to swimm with me, but this is another story.

 

First, before pics, look on this drawing to understand how the chrono hand runs on the A7750 with what I call a "floating assembly". Probably there is a more appropriate word.

When you press on the start/stop chrono pusher, the mechanism push on the bellcrank.This one turns on his axis and engage the teeth, on the top of the stem, with the chrono gear. The teeth on the bottom are already in contact with the movement seconds gear.

Thinking about this, IMHO, THIS COULD REASON OF A JERKY SECONDS AT SIX. The stem being constantly in contact with the movement seconds gear, the stem is constantly turning with the seconds gear. This should create lot of drag and vibrations amplified to the su-dial at 6.00 gear train. I observed this. The design is not very good as the teeth on the bottom of the stem are square angled and just seated on a square cavity.

The bottom of the stem is jamming, or hang up if not properly oiled and the movement stops to run.

 

 

A very problematic little part

 

THE CURE

Using a very little oil pick or a seringe, put a big drop of oil at the bottom, in the cavity where the seconds gear is in contact with the stem teeth. This area need a serious amount of lubricant. Oil also the seconds gear dents and the big chrono hand gear.

You can also control the frictions of the stem teeth via the little adjusting screw. For this, chrono stopped, turn gently on both ways the screw and stop when the stem stop to jerk. Then engage the chrono to see if the bellcrank moves enought to allow the contact between the stem and the chrono gear. Tricky job...

 

 

THE OVERTRAVELLING PROBLEM WITH THE CHRONO START/STOP LEVER

As explained in the part 1 (see the part 1 for a complete problem description) this happen randomly and could be the fact of a bad design. It should be possible to correct it, but it need time.

 

To understand what is going on, look the chrono fonction sequence :

On all following pics, the chrono transmiter servicing hole is red circled. You can see the stem teeth. I have put red points on the distributor and the part who is problematic so you can see what happen there. I put also a green point on the reset articulated lever.

Its interesting to know how the chrono hand and the minutes counter hand return at zero. The lever articulated part is like a hammer who knocks on a ovoïdal wheel on the hands gears. This design allows,in any position, the hands returning at zero.

 

 

1) The chrono is non-engaged

 

2) The chrono is started. Randomly the little part 1 overshoots on the right from his way probably a result of inertia. This part now will stay against the reset pusher arm (2). At this point, if you press again to stop the chrono, doesn't work. To cure, just press the reset pusher, the part 1 will return in good battery, and now you can stop the chrono hand.

 

3) The chrono is stopped.

 

4) The reset.

 

 

 

 

At this time I will probably add a kind of part 3 as a conclusion. But for me its not necessary to go further in disassembling. Of course, I can disassembly the primary chrono plate, and then the movement also. All the flaws and failure I got on my Daytonas was cleared here.

Another precision:

The watches whitch I got troubles arrived with damages during shipping, I mean, shock on boxes and so. May be this is a reason when you got a Daytona half dead... these movements are fragile and from China to Europe or USA, the way is long, with a lot of bad care from people working in airports or from shipping companies

Edited February 6, 2009 by RolexAddict

[bme 4]

Wow...........someone send this to Fakey!

 

Wow...........someone send this to Fakey!

[onzenuub 363]

I am speachless.

[greg_r 107]

:drunksing: :notworthy: :notworthy: :notworthy: :notworthy:

 

Awesome, RA, simply awesome.

[Poohmonster 0]

Absolutely fantastic stuff RA.....well done mate..........I must say the inner workings of a watch really are amazing but I just cannot bring myself to dabble in it......to me.....it just needs to look good......if it breaks I buy another one....

[sconehead 5]

Bravo...well done, here's a link courtesy of Pugwash for an ETA 7750 which will explain a bit better how the pushers work.

http://pugwash.info/eta/eta.zip

[onzenuub 363]

Bravo...well done, here's a link courtesy of Pugwash for an ETA 7750 which will explain a bit better how the pushers work.

http://pugwash.info/eta/eta.zip

 

 

Think this one works better: http://pugwash.info/eta/7750/7750.html

[sconehead 5]

Correct onze, but you can save my link onto your hard drive...oke?

[onzenuub 363]

Correct onze, but you can save my link onto your hard drive...oke?

OKE

[RolexAddict 1]

Thanks for your interest guys

 

Bravo...well done, here's a link courtesy of Pugwash for an ETA 7750 which will explain a bit better how the pushers work.

http://pugwash.info/eta/eta.zip

 

Thanks for the link, I didnt know this,

very well done and better explained than me, but I was not so far from these shematics

 

I will read again these 2 parts to edit and make little corrections because my franglish is... just franglish

 

Looking the chrono devices disassembling on this link, I understand now why I got the same spring twice in my face and have lost one one time in the carpet..

Edited December 16, 2008 by RolexAddict

[trailboss99 1,086]

Absalutly brilliaent RA. Very well researched and I think you may have well cracked it for at least some of the dead sec@6s around. Well done.

 

Well Fakey? What you say?

 

Col.

[alphakazi 0]

excellent contribution RA - it's posts like this that build on the quality of the forum

[oscarmadfish 0]

great stuff RA

[AllergyDoc 42]

Well done again, RA! I still haven't put the drop of oil on my seconds-at-six Tona. But I will get to it, maybe this weekend.

 

Thanks for taking the time to do this and stick around.

[RolexAddict 1]

Thanks AD,

We have to re-build this board, we will do it.

No problem, only solutions.