Jump to content

Another 7750 Disassembly

sstakoff
 Share

Recommended Posts

clockboy Distinguished Member

clockboy

Posted
Posted

Another 7750, I have serviced many of these, the industry standard chrono. Always annoying when dis- assembling a watch movement to find previous poor workmanship. This seems to be very common lately. However nice clear vid. 

Link to comment
Share on other sites
CaptCalvin WRT Addict

CaptCalvin

Posted
Posted

Few things I noticed here:

It's missing the dial washer.

Your instruction about the day and date synchronization is erroneous. With the day driving wheel finger pointed at the mark on the plate, the finger for the date driving wheel needs to point at the top of the pivot for the day and date intermediate driving wheel, not the canon pinion.

The "lock" locks the chronograph seconds when the chronograph is paused, and does not lock the minute recorder.

There's no reason to have to pry the cam jumper over the cam to remove it, just remove the cam first. With the cam screw removed, simply pull the cam jumper slightly away from the cam and the cam can be lifted up without trouble. No need to subject the jumper to awkward bends.

That fourth wheel is most likely not original to the movement. Never seen an ETA 7750 fourth wheel with the rim that thin. I have seen one with this exact geometry and that came from a Chinese Dandong 7750 clone.

  • Like 1
Link to comment
Share on other sites
sstakoff WRT Addict

sstakoff

Posted
  • Author
Posted
58 minutes ago, CaptCalvin said:

It's missing the dial washer.

 

Good point - I'm sure this is causing issue with the day wheel.

59 minutes ago, CaptCalvin said:

Your instruction about the day and date synchronization is erroneous. With the day driving wheel finger pointed at the mark on the plate, the finger for the date driving wheel needs to point at the top of the pivot for the day and date intermediate driving wheel, not the canon pinion.

 

Oh goodness!!! You are so correct. I always consult the tech pub when assembling so I would have gotten that. Serves me right for going from memory :)

1 hour ago, CaptCalvin said:

The "lock" locks the chronograph seconds when the chronograph is paused, and does not lock the minute recorder.

 

Yep - correct again!

 

1 hour ago, CaptCalvin said:

There's no reason to have to pry the cam jumper over the cam to remove it, just remove the cam first. With the cam screw removed, simply pull the cam jumper slightly away from the cam and the cam can be lifted up without trouble. No need to subject the jumper to awkward bends.

 

I've never tried this, but I am absolutely going to do so next time. I assume you can use the reverse of this to reassemble. That's always been a pain for me as well.

 

1 hour ago, CaptCalvin said:

That fourth wheel is most likely not original to the movement. Never seen an ETA 7750 fourth wheel with the rim that thin. I have seen one with this exact geometry and that came from a Chinese Dandong 7750 clone.

Not surprised - this watch has a somewhat questionable history :)

 

Thanks very much for your careful analysis and commentary. Truly helpful. I will also add these corrections to the commentary in the YouTube video.

 

Stu

 

 

Link to comment
Share on other sites
 Share
Go to topic listing


  • Recently Browsing

    • No registered users viewing this page.

  • Topics

  • Posts

    • RichardHarris123
      Setting lever spring

      By RichardHarris123 · Posted

      I'm assuming that every time you set the watch you are work hardening the detent spring, maximum hardening is  where it meets the plate due to maximum deflection.   That's why it snaps there.  The Young's modulus may be the same but after it's reached its maximum yeid strength it breaks.  My mechanic engineering is very rusty, correct me if I'm wrong. 
    • Neverenoughwatches
      Setting lever spring

      By Neverenoughwatches · Posted

      Ah ok yes that makes sense to polish it where the arm starts to form from the body of the bridge, i thought you meant the underneath of all the arm.
    • JohnR725
      Epilame / Fixodrop

      By JohnR725 · Posted

      this is something I've never quite understood about the some of the Swiss companies. In 1957 Omega was using 9010 for the keyless parts with epilam. there's been a slow migration towards using heavier lubrication's but still typically oils and epilam to keep them in place. When it seems like 9504 works so much better.  
    • nevenbekriev
      Is this a 'hack' ?

      By nevenbekriev · Posted

      OK, welcome in the world of alarm clocks... I guess the 4th wheel is dished because it is from another movement. If it was not dishet, then it would not mesh with the pinion of the escape wheel, am I right? The marks of wear on the 4th wheel pinion doesn't corespond to the 3th wheel table position, at list this is what i see on the picts. Calculating the rate is easy - there is a formula - BR = T2 x T3 x T4 x T5 x 2 /(P3 x P4 x P5) where T2 - T5 are the counts of the teeth of the wheels tables, and P3 - P5 are the counts of the pinion leaves. Vibrating the balance is easy - grasp for the hairspring where it should stay in the regulator with tweasers, let the balance hang on the hairspring while the downside staff tip rests on glass surface. Then make the balance oscillate and use timer to measure the time for let say 50 oscillations, or count the oscillations for let say 30 seconds. You must do the free oscillations test to check the balance staff tips and the cone cup bearings for wear. This kind of staffs wear and need resharpening to restore the normal function of the balance.
    • RichardHarris123
      Any tips to correct a sloppy error?

      By RichardHarris123 · Posted

      Glue a nut to the barrel lid, insert a bolt, pull, disolve the glue.  Maybe someone will have a better answer. 
×
×
  • Create New...