Another 7750 Disassembly

[sstakoff]

Spent a bit of time in my workshop.

https://youtu.be/RYNeRiDdPQE

 

[clockboy]

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. 

[CaptCalvin]

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.

[sstakoff]

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