Seiko 7A38 - by the numbers



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Forum Home > Bend it, Mend it - Mods & Wreckers > Two 7A's in one day

Sir Alan
Posts: 458

I'm pleased to say that I've finally put my nemesis main bridge in its place both metaphorically and literally. Having proved to myself that I could do it (using my new stereo zoom microscope) I intended to finish what I started nearly 3 years ago, namely a complete strip down of a 7Axx movement, clean and rebuild.

To be honest its been such a long time that I wasn't quite sure about the the two movements I had in parts - when I inspected the two main plates one of them had the broken off stud for one of the switches, the other appeared to be missing a stud completely. So, rather than building a movement that might be flawed, I decided to rebuild one of my spares - this one being a 7A28.

It looked relatively cleanand I was reasonably sure it worked, so I cleaned a working area and set about stripping it down. I've been refining my techniques as I go, and lately I have switched from using my ultrasonic cleaner on movement parts and now use a combination of essence of renata and rodico. because I can inpsect each part in minute detail (at 50x magnification) I can be sure that each part is clean.

Here's the centre wheel having a bath:

those little flecks weren't there before I put it in.

Here's the main plate nice and clean:

and here we go adding parts

I did have to refresh my memory on how the keyless works went together

before I started to assemble the gear train, I decided to demagnetise all the gears using this:

here's the gear train in place:

and just a few minutes later the bridge is on

I spent hours and hours and hours trying this before - I simply couldn't see what I was doing through the loupe.

Once I have a bridge on, I oil using this:

Then it was on with the other two bridges. This one:

took me longer to get back on than the main bridge!!

but patience was rewarded. This other bridge was easier. Then it was back on with the coils

and then the switches

and then the final bridge

at this point my battery ran out, so you'll have to believe me that the last few steps went ahead without hitch.

I fitted a dial and the sub-dial seconds hand, pulled the crown out to 2nd click, fitted a battery, pushed the crown home and ........... life.

I then tested all other functions and put the movement into my working spares tray.


After tea I decided I was on a roll and I'd do another. I've got a 7A28-7020 (the first one I bought) that came to me in pretty terrible condition, both internally and externally. I'd cleaned it up as best I could and was pretty happy with it (all bar the tachy ring) but annoyingly it had a habit of stopping completley or losing several hours. It sat in the box feeling sorry for itself for ages until recently I picked up another one in much better condition, but without a bracelet. So, I robbed the bracelet from the poorly one and promised myself and it that I would get round to sorting it. Well, tonight was the night.

I stripped it completely, taking pictures as I went. Unfortuantely these were under my desk lamp so have a horrible colour cast to them.

I found evidence of serious over oiling - I think the previous owner had tried to sort the problem out by just adding more and more oil.

And once I got under the main bridge I found the problem:

this fleck of rust / solidified battery leak was stuck to the centre wheel - it must have been fouling on the third wheel as the gear train turned. The oil was actually keeping it in place.

Here's the gear train having a bath:

this second movement went together really quickly and easily - it wasn't long before I had the green spacer block on and fitted the rotary switch

then the circuit

and the back plate and battery plate

then dial side

and finally a dial and seconds hand

and life.

I've been away from the 7Axx fold for a long time, but I return a better watch tinkerer.

March 22, 2015 at 7:49 PM Flag Quote & Reply

Site Owner
Posts: 13276

Well done Simon - you've come a long way in 3 years. ;)

March 22, 2015 at 8:10 PM Flag Quote & Reply

Sir Alan
Posts: 458

Thanks Paul - and I'll never forget what started it all.  ;)

March 22, 2015 at 8:52 PM Flag Quote & Reply

Posts: 568

Great photo's---Most helpful  :)   Hats off to you :D

March 22, 2015 at 9:30 PM Flag Quote & Reply

Posts: 13

This is a wonderful me courage to continue my own efforts.

But I have to ask, what is "essence of renata?" Sounds exotically erotic, and surely isn't.

March 25, 2015 at 9:13 PM Flag Quote & Reply

Posts: 13

Ah, never mind the question...looked it up...something like "One Dip" it seems...

March 25, 2015 at 9:21 PM Flag Quote & Reply

Posts: 508

Congrats, Simon...Very happy you finally mastered the ancient art of Seiko 7Axx main bridge resetting :P


My personal Blog:

March 26, 2015 at 6:10 AM Flag Quote & Reply

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