Eta 7750 Service Walkthrough - The Industry Standard Chronograph

[clockboy]

I have serviced a few of the 7750's which is the ETA's standard Chrono movement. However I recommend getting the correct movement holder for this movement. It makes it so much easier when aligning the hands and also helps avoids moving the centre jewel when pushing on the hands.

[georgew77]

Hi Lawson,

I signed up on this site just to thank you!

I never disassembled a mechanical watch, not to mention assembling.

However, based on your walkthrough, I disassembled, reassembled the watch and in the process fixed it`s problem.

I found my problem at the keyless works: the castle pin did not allign with the cannon wheel. The castle pin was sliding under, not engaging. I could not set the date nor time. I hopped for not needing to do a full dis/assembly but I ended up doing it anyway. It was a hamilton frogman chrono.

Many thanks again Lawson! 

Now, because all this was uncharted territory, it took me more than 4 days for the whole thing. I had some difficulties in several occasions, based on the walktrough and if you are curios, I can mention them and maybe you could use them to further improve your great tutorial? 

best regards,

./george

 

[AP1875]

Many thanks again Lawson! 
Now, because all this was uncharted territory, it took me more than 4 days for the whole thing. I had some difficulties in several occasions, based on the walktrough and if you are curios, I can mention them and maybe you could use them to further improve your great tutorial? 
best regards,
./george
 

I’m glad you managed to repair your watch. I will also attempt to service a 7750 and will definitely be using this guide as a reference point.
I’m curious to know where you had some issues with the reassembly?



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[georgew77]

20 hours ago, AP1875 said:

 

I’m glad you managed to repair your watch. I will also attempt to service a 7750 and will definitely be using this guide as a reference point.
I’m curious to know where you had some issues with the reassembly?



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I am sorry, but I sacrificed to much time with the watch and I did run out of time to respond. It,s the reverse wheel positioning that after montig the last bridge of the chrono, prevented the ability to arm the spring via the crown. I had to dissassemble and reassemble the last 2 chrono layers 3 times, including the fidling with the oscilating pinion each time.

 First time, I screwed the ratched wheel with the impropper screw. I thought that this was the reason causing the whole chrono to fail. The ratchet wheel needs a smaler one than the norm. Then I thought that maybe the  reduction wheel protudes in the holes of the ratched wheel and blocks it. This was tricky to me. The reduction wheel with the reverse wheel caused nightmers for me. 3rd time it worked and i am not sure what was the real problem.

Another thing was the double corrector. "Install the Double Corrector, making sure the spring is correctly positioned. " I was looking for that kind of spring for hours. No sir, no spring found. Nor did I had a clue how it should look like. In the eta manual I also could not idetify that spring. I thought, that’s it, end of storry. Then, after a while scratching my neurons and trying to understand what it should look like and if I might concot one myself, I tried tonunderstand how it works and to me, it works without such a spring. Maybe there was none in the first place. no ideea, it works fine.

When installing the chrono, it is mentioned to let the crown in the time setting position till the end. It might be still ok to check actuallythe heartbeat between each bridge mountig.

Installing the switch to the cam, as in the picture, caused me some problems later. I couldn’t turn it as later needed to install other pieces. I had to redo and position else, after I got how it should work.

I might have understood a lot wrong or because my total lack of any experience, but thesewere my downs. All in all, maybe not for a noob like me, this is an awsome guide and that’s why I regestered here to give my thanks to this work of art.

 

 

[Lawson]

I have been notified that the links to the PDF's of the 7750 walkthrough have been damaged.

I have re-uploaded them to help all those wanting a copy

 

ETA_7750_Service_Walkthrough_-_Assembly.pdf

ETA_7750_Service_Walkthrough_-_Disassembly.pdf

[mlfloyd1]

Lawson you have done us a great service with this walkthrough; thank you kindly.

Can you tell me where you got the stereo clip-on magnifiers that you show on the last page of your disassembly?


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[Lawson]

On 12/3/2018 at 8:47 AM, mlfloyd1 said:

Lawson you have done us a great service with this walkthrough; thank you kindly.

Can you tell me where you got the stereo clip-on magnifiers that you show on the last page of your disassembly?


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Thank you mlfloyd1 and all the other how have left such kind words.  I'm glad this walkthrough has been a blessing to you all, and I hope it continues to inspire and encourage others to take on this movement.

In regards to the optics I use, they are made my Zeiss, and are called Eye Mag Pro.  They are mostly designed for the medical industry, for neurosurgeons etc..  I created a thread on them here mate:

They are not cheap, but I was working in the industry at the time, using them 8hrs a day 5 days a week, and could claim them on my tax return

If you can afford them, they are LIGHTYEARS ahead of anything on the market, and have an unconditional lifetime replacement warranty.  I would never part with them at any cost.

[Highballn2]

I'm devastated just hours ago I dropped my first ever automatic watch with the 7750 Valjoux movement, now it's completely dead and yet the rotor spins as it did first day I ever wore it, no other watch in my collection tops that Oris TT1 because it was my first real watch I saved entire summers worth of pay to buy.  I woulda rather dropped my Tudor or Muhle.. greatest movement ever. Thank you for this wonderful amazing breakdown. 

[margolisd]

Fantastic walkthrough. Thanks so much. Just one thing. I have this washer left over and I’m not sure where it goes 

[nickelsilver]

That just goes in the center, over the day ring. The dial keeps it in place.

[margolisd]

Oh yes... duh! I’m being stupid. Cheers.

I have to say I found this quite challenging in places. It’s a very clever and economical design. But not so easy to assemble. I personally prefer the Omega 861. Takes me about half the time.

But what a great walkthrough!

[nickelsilver]

After you've done a few they take the same time (or less) than an 861. Even with the additional complications of automatic and date.

[margolisd]

Do these regulating pins look correct? I’ve not seen these kind before. I feel like I want to twist them anti-clock. I’m getting funny readings where I get everything perfectly regulated then randomly get a 4ms beat error. Then a tap on the movement with tweezers clears is. I’m wondering if the hair spring is getting slightly trapped between the pins.

[nickelsilver]

That's part of the Etachron system, by twisting the block you can adjust the gap. The spring should be bouncing from one side to the other, the effective gap being approximately equal to two hairspring thicknesses or slightly less.

[jdm]

2 hours ago, margolisd said:

 I’m getting funny readings where I get everything perfectly regulated then randomly get a 4ms beat error.  

Even before that, which amplitude are you getting across at least 3 positions? 

[margolisd]

290. It’s healthy. I think there was some sticky on the pallets or hairspring. Good soak in one dip seems to have fixed it.
 

I did think the end shake on the pallet fork seemed a bit extreme... was thinking of lowering the upper jewel slightly. The jewel in the pallet fork cock looks as if it can come down a bit. I wonder if it’s been moved during a previous service.

This chrono has been hard work. 3 times I’ve been ready to close the patient I’ve realised something isn’t right and had to go back in. But I’m learning the movement!

[DouglasSkinner]

Just came across this!  Thanks for all the effort you put into it.  I was unable to download the PDF.  Something may have happened to break the link.  Again, thanks!