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Discussion Starter #1 (Edited)
Cosmotron 7803A - Movement Ring Advice

I was quite excited when my Cosmotron arrived, it being my first electric watch. You can imagine my disappointment when I noticed something wasn't right. It felt a bit rattly so I took the caseback off and this is what I found:





To my untrained eye there are two things wrong. Firstly he battery clamp (not a big deal at the moment) secondly, and my biggest concern, the movement ring.

Fortunately the watch didn't cost much (certainly not worth disputing it and sending it back) plus I do like it and everything else seems to be in pretty good nick.

Now, I suspect that specific movement rings (either NOS or AM) are in the same category as hens teeth (certainly haven't uncovered any on web searches), what is the best approach? The movement is 12.5 ligne and a number of online sellers sell job lots of 12.5 ligne spacers. Is it worth buying a bag full in the hope that one will fit? Is it easy to resize one so that it does fit? The ring may not be the correct one as it appears to have a tab which covers the screw hole just above the pusher in the photo.

I was also expecting to find I would need some screws securing the movement to the case or ring but there were none. Scrutiny of photos of the same movement suggest that they aren't required.Would this be correct?


Any help will be much appreciated.
 

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I have tried to make a little progress on this and recently bought a pack of blank plastic rings of the correct size. I have had a look at fitting them but have already hit a couple of stumbling blocks..


Firstly the movement doesn't quite site nicely within the ring as there is a tiny lip just beneath the dial (not the dial itself) which means the movement doesn't go all the way into the ring. I expected it to fit snugly without having to force it in. Is this a realistic expectation or should the fit be more of an interference fit?


Doing a little more research the original ring looks to be quite a bit more complicated than just a sleeve to fill the gap between case and movement. There are the usual gaps for the crown and the pusher but there are also crenelations and a tag or two. Hopefully they aren't too important but I expect I'll find out when I have modded the generic ring to suit. If only I had a modelling lathe...
 

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I have started buying and servicing some of these 78XX movements.
They are very interesting in the leap from mechanical to electrical.
I would not worry about the movement holding ring, you have over 75% of the original there and if it does not rattle in the case I would live with that. You will also need a flat case back gasket.
I have another cosmotron coming in for spares and may be able to part out that ring if all goes to plan.
Good luck and PM me if you need help.
One from the stable....
 

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Discussion Starter #4
I have started buying and servicing some of these 78XX movements.
They are very interesting in the leap from mechanical to electrical.
I would not worry about the movement holding ring, you have over 75% of the original there and if it does not rattle in the case I would live with that. You will also need a flat case back gasket.
I have another cosmotron coming in for spares and may be able to part out that ring if all goes to plan.
Good luck and PM me if you need help.
One from the stable....

Thank you for the advice Melt. Unfortunately the movement dose rattle which has caused some slight damage to the dial. Also, if I press the rest pusher the movement moves and stops.


Thank you pointing out the lack of washer, I hadn't spotted that. Seems fairly obvious now.


Some images of the ring, especially in-situ, would be a great help.


I'll PM once I am able to take another look at it.


The watch in your photo is is very elegant, especially the concealed crown although I expect it is difficult to set.



Thanks again for the advice.
 
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