THE ASIAN 7750 SECONDS AT 6.00

[RolexAddict 1]

 

THE A7750 MOVEMENT PART ONE

 

This is a technical review of the A7750, last edition, - 28.800bp/H - second runing at 6 o'clock sub-dial.

Its a complete reconstruction of the first rewiew I started on the former board.

 

This is made to help especially rep lovers who wants to start with a sec. sub-dial at 6.00 to understand what happen with this "so terrifying movement" and how to fix a failure. Also to show and prove with pictures that the second at 6.00 gear plate is more simple as supposed, and demonstrate it is not responsible of the entire failures and jerky second hand motion.

 

This review is also made for newbies, so I apologize to be repetitive for those who has already a good background in watch mechanics and know already what does mean a "complication"

 

BEFORE TO START TO READ AND BEFORE TO SAY "MY DAYTONA IS DEAD":

THE FIST THING TO DO BEFORE TO WEAR A DAYTONA AND TO PLAY WITH THE CHRONO PUSHERS...

You need to wind the watch. If a few gentle shacks are suffisant to keep the movement running and kipping good time, ITS NOT ENOUGH to endure the running chrono. This movement need only a serious power reserve to run, especially when the chrono is engaged. Not enough power, the movement will stop to run if you engage the chrono fonction.

WIND GENTLY 20 TO 40 LITTLE TURN, SLOWLY, THE SPIRALED MAINSPRING IN THE CYLINDER IS VERY FRAGILE.

 

INTRODUCTION

A few month ago, my first Daytona purchased stopped to run after a couple of days. My ignorance was to think "the movement is dead because it is a inferior Chinese movement". It happened one day when I started the chrono and the watch stopped to run after 30 seconds. I pushed many time the start/stop pusher... no way. I pushed the reset pusher, then the the chrono hand returned at zero but the watch was still dead. I shaked it. Started again, but dead again after a few minutes.I wond it a little, dead one more time after a few minutes. Curiously, when I wear the watch, it was running well... This is the number one common failure. Later, I had also troubles with the chrono start/stop pusher on another Daytona. This is the number 2 common failure. Then, a third problem appeared on one of my Daytona : the jerky second hand at 6.00, and also the iregular chrono hand sweeping. This is the failure number 3.

 

So, 250 USD... pfff, lunch money, lol. So I decided to disassemble the movement steps by steps, learn to re-assemble, and try to understand what was wrong.

 

 

This is what you can see when you open the case back and remove the rotor :

It's the chrono module with the poor auto wind system on top. Only 3 gears loading on 1 way the main spring

Later I will make comments on all other parts and show you how it works.

THE LACKS OF THE A7750:

this movement doens'nt have a regular automatic module. Just a rotor, a occilliating mass including a ring with teeth a "kind of gear" molded or glued in the rotor who is in contact with a 3 real gears reductor who is directly in contact with the mainspring cylinder to load it. When the rotor turns counter clockwise (looking from the back face), he is free. Turning clockwise (looking from the back face), he loads the mainspring in the cylinder. This means, even if you wear the watch all the day and have a regular and natural wrist motion, the rotor tendancy is to turn counter clockwise, as its easier for him -no resistance-, and it will make a very few clockwise rotations so the mainspring will be all the time very loose and weak. The main problem of this movement is the lack of the automatic winding system.

 

THE COMMON FAILURES REVIEW AND HOW TO CURE :

 

The A7750 number 1 common failure: the brocken mainspring

lot of watches come with a brocken/damaged mainspring in the cylinder. When he is not brocken, often the mainspring is stuck by dry oil/grease inside the cylinder. There is a serious risk he collapses when you wind the watch.To run properly, to have flawless chrono fonctions, the watch need to be wond manually, I will say minimum 20 turns to give it a shoot. This has to be done GENTLY.

Winding the watch, you will notice if the watch came with a brocken mainspring or not inside the cylinder. No clicks or crack sounds. Just the feel of non resistance, a loose feeling on the crown after 20 turns. You are winding "in the air". So what now ?

The cure:

Throw the watch ? No. The watch will run normally, keeping good time, but even if you wear it a full day, it will stop during the night.The watch is not dead, but has not power reserve. Wear it, keeps good time, you will just have to set the time every mornings... or use a watchwinder for the night. But remember the non-efficacity of the rotor... so you keep a running watch but little handicapped for a abusing chrono use.

 

The A7750 number 2 common failure: the over travel of the start/stop chrono lever.This happens on lot of watches.

The symptoms:

You press the start/stop pusher to engage the chrono. The chrono hand runs. You press again the start/stop pusher and the chrono stops. Now if you press one more the same pusher, the chrono starts again. Press again... the chrono hand should stop again, but now it doesn't and the pusher became "soft" under finger pressure.Impossible to stop the chrono hand to run...

From time to time, the start/stop lever overtravels from his way, I try to find the solution to fix it...difficult. This is a lever design error. But no panic! Its not a big problem, and this happen randomly.

The cure:

If you press the start/stop pusher when the chrono hand is running to stop it, and if you get the "soft pusher feeling", and the chrono doesn't stop...

Keep quiet. Just press the reset pusher, it will put everything at zero and of course the chrono hand will be stoped and returned at zero (12) Then you can play again, the chrono will start and stop again. Nothing broken. Always you have this failure, press the reset pusher.

 

The A7750 number 3 common failure: jerky second at 6.00 hand / chrono hand sweeping

Now we enter the eternal polemic of the second at 6.00 gear train...

In most of case this can be corrected without pull out from case and disassembling the movement. Just by opening the case back and remove the rotor.The A7750 like all chronographs uses a little round stem toothed on each extremity to transmit the motion from the movement primary seconds gear to the chrono gear. This stem in animated with a precise cinematic and the motion is transmited by a spur (bellcrank ?) who is relied to the start/stop pusher by a lever. This bellcrank can be ajusted via a spring and a regulating eliptic screw. In fact, the teeth in contact with the movement primary seconds gear need a good lubrication. The other side, the teeth in contact with the chrono gear need to be ajusted to assure a firm contact and avoid jumpy motion. If this disposal is not enough oiled and/or the bellcrank is not well udjusted, the result is drag and vibrations. These vibrations are amplifyed in the gear train and are one of the reasons of the jerky second at 6.00 and also a non soft chrono hand sweep.

The cure:

To adjust the spring tension you need only a screwdriver... To oil the movement second hand you need to disassemble the rotor to have a access to a servicing hole. You will need also glasses/magnificer and a seringe or a very thin oil pick. That's all.

We will see this in details with pics in the part2.

 

THE CRONOGRAPH MOVEMENT

The A7750 concept is not an inferior Chinese movement design. He works exactly like all other brands called Lemania, Valjoux, Seagull, Zenith, even Rolex, etc. All these brands use probably better material as real jewels instead of pink plastic... and better metals for parts and springs. AND ALL IS PERFECTLY LUBBED. For this, the A7750 can be called inferior. Cheap dry material, but if oiled, works well! the concept is good. And all chronos modules on all kind of chronos use the same cinematic design for start/stop and reset mechanisms. But you will discover that this movement is not so "chip built" in fact, it's a very good movement !

 

A chronograph is a movement with complications. What is a complication ?

The add of a day and/or date disk is a complication. The 4th hand to track a second time zone is a complication. Also a power reserve indicator, etc. Basically you have the movement itself: a suite of springs, gears and spiral/regulator who drives hands for hours, minutes and seconds. The mechanical background. Then you add a floor plate for the day/date feature. Another floor plate for a 4th hand etc. The plates are located on the dial face of the movement.

For a chronograph movement complications are a little more sophisticated. Floor plates are located on BOTH faces of the movement. The pushers arms, levers and bellcranks are located at the bottom, on the case back face. The gear trains are located on the top, the dial face.Some features and parts are passing through the background movement. like the chrono hand gear who is located on the under face, the case back side.This gear has a very long axis crossing all the unit.

Other exemple, the hours hand reset arm (sud-dial ar 9.00) is located on the dial face, under the sub-dial gears floor.

 

Here a shematic of the A7750 building. Note, its EXACTLY the same principe for almost all existing chronographs

 

To see how are real things, here the bacground movement, dial side. The primary gear module and the seconds at 6.00 modules have been removed. You can see the yellow movement seconds gear

 

The other side, all chrono features have been also removed

 

Here, a view all the primary disassembling: Not a big deal, but tricky to reassemble... This pic was made for the former article, the hair spring for the chrono hand contact adjustment is missing, it has jumped on the carpet... lol, my wife found it back...

1) dial side, the fist plate is removed, under you see the second plate witch is the seconds at 6.00 module and his 4 gears including the seconds sud-dial gear. No 11 gears, no mystic, just 4 little gears, and partially jewlered. We will talk about this furter.

2) The background movement with his primary gears used for the hours chrono counter and reset device. As I wrote above, the reset pusher lever has 2 arms, the minutes counter and the chrono hand reset arm is located on the chrono module face. The Hours counter arm is located on the primary gears module, under the seconds at 6.00 module.

3) The case back side:

A)-The rotor and the poor automatic system... framed in red, the 2 gears and the mainspring loocker. And then the first floor with the pushers arms, bellcrank and stem.

The second floor who retains the chrono gear, the one by one minutes counter spring and the start/stop pusher lever main spring.

THE SECONDS AT 6.00 MODULE

Now there is something interesting... the mystery of the seconds at 6.00 emblematic gear train...

Funny we have read a lot of things about this concept, no jewlered, 11 gears, etc. Like St Thomas, I believe only what I see by myself. So the best is to wear glasses, take a screwdriver and disassemble the watch to inspect the mystery inside. It's not a big deal. Only 4 gears, the seconds sud-dial gear included.

Here, what you see after removing the dial. I marked the sub-dial hands axes whit a marker

 

Then, what you see after removing the first plate, the famous seconds at 6.00 gear module. I put the numbers from 1 to 4 so you can understand. Only 4 gears, no 11. This doesn't create drag. the other gears you see left and right are for the hours and minutes counter sub-dials. There are not in contact with the 4 seconds gears. It looks like on the pic but they seat deaper on the floor plate, the floor plate is thick and has 2 levels. The arrow shows you the movement seconds gear located under the sud-dial hours counter hand gear.

 

Here, I made a drawing of the seconds at 6.00 gear train

 

About the jewlered gear axis : Sub-dial gear axis on the top plate just under the dial are jewlered.

 

Curiousely, The axis on the plate where gears are seated has no jewels. Just holes in the plate. Except for the minutes counter at 3.00. Why ? I don't know. This axis is used at the same time by the mainspring cylinder. So may be it's for that reason.

 

 

Now, my opinion, observing how all this stuff is working, I don't think that these 4 gears are drag responsible. Gears can be oiled of course, also coated with graphite powder... If they are just partially jewlered, there is reasons. When I disassembled the module, my fingers was like geasy. I thing makers use a kind of spayed epoxy base coating. This is called a self lubricating coating. The Zenith El Primero was not oiled/greased but all axes and parts was coated with bisulfure of molibdène (epoxy) applied by vaporisation process. The Rolex company changed this for a regular oiling/grasing chart.

But pay attention when disassembling the A7750, you ned good tools and a minimum of skills, all parts are very fragile, especially sub-dial hands and gears axes. Its really a tricky exercise.

 

The part 2 will explain steps by steps how works the chrono and how to cure the jerky seconds hand, and adjust the chrono starter bellcrank. Also what must be oiled.

Edited February 6, 2009 by RolexAddict

[greg_r 107]

WOW.

 

Fantastic post, RA - can't wait for part II

 

[onzenuub 363]

And again a great post from RA, thanks.

[AllergyDoc 42]

And now I know why I don't work on watches. Maybe the oiling part (he's yet to explain), but taking the movement apart? I get the willies just thinking about it.

 

Great work, pal! You need to settle down and quit flying all over the world, partying like you were 20. That way you can work on our watches.

[RolexAddict 1]

Thank's guys,

PART 2 this week-end, the end of the A7750 mystic

[oscarmadfish 0]

great work RA

[Demsey 9]

WOW.

 

No doubt!

 

Great RA. I'm going to savour this and not try to absorb it all too quickly. Are you on reserves? When do you have time to fly?!

 

Just a note of encouragement here. When I first registered RWG, the board was VERY MUCH what this one is now. Save the obvious fact there were more registered members and more posts. BUT the level of knowledge of members was LESS than there is here, in the now, believe me.

 

My first real try at a proper watch review was my third, the 16520. I followed a 'soup recipe' form that member 'Neo' had developed, and it was basically a 'fill in the blank' deal.

 

I was intrigued by the Daytona (there was no genuine 116520 at the time, so the whole seconds @ six aspect was not an issue) and it's flaws of 'subdial spacing' and Asian copies of the Valjoux. 'Omni' schooled me in quick fashion, I got a handle on it and did the review with a lot of 'internet gleaning' of infos of the reps and the genuine. Another 'noob' 'Ziggyzumba' gave kind compliments on the review's 'technical' attention to detail.

 

Some weeks, to months later, after members were bemoaning the reliability of the then "b" model 7750's, Rob (Ziggyzumba) set the forum on it's ear with an amazing tear down review of the movement, repleat with seeming "scanning electron microscope" shots of worn gears, missing jewel caps and broken and bent 'watchamacallits' and forensic style investigation. It came out of nowhere, floored everyone and the forum just took off. He set a standard that never was bettered, but it wasn't for people's desire to try; or to at least contribute to their best ability.

 

Another new guy PMed me about a 16613 review I did, and commented he had visited the review daily and was apologetic about being an inquisitive noob and generous with compliment. He now sets the standard for 'Review'; By-Tor.

 

Then came Nanug, Ubiquitous, Eunomians, and a flood of other experts that relegated my contribution to; "Just buy from Joshua, do a 'Search' before you get the Daytona."

 

There has been some concern about 'recovering database' from RWG to have a good archive of useful info. I think it were rc42 who recently made comment; "So much was repeat, repeat, repeat information..............." True. In a year's time this board will be as good or better than RWG ever was. And will have done it from the ground up.

 

For one, the attention of a webmaster who gives a toss.

 

This post is this version of RWG's new standard with regard. I do plan on researching the DW 6263's to perhaps the poin tof purchase. Then? Fuck, a review I guess.