Seiko 7A38 - by the numbers

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Forum Home > Parts Info, Tech Tips and Tinkering > 7A38-7020 with unknown chronograph fault

My7A
Member
Posts: 4

Thanks to Paul for opening this thread for me.


So here's the story: I'm a total newbie, only got this 7A38-7020 a couple of weeks ago from our local auction website (ricardo.ch):


https://www.ricardo.ch/de/a/seiko-chronograph-herren-armbanduhr-1079809004/





The description said "watch works" and it's basically true, the watch does work, only the Chronograph feature doesn't, which is ok considering that it wasn't very expensive.


Still, now that I've got the watch, I have started to wonder if there might be a way to get the chronograph feature working as well. Perhaps by a movement swap? And so I wanted to start a thread in the tinkering subforum in order to ask if all 7A38 movements are the same and therefore interchangeable.


I suppose the font used on the day and date wheels aren't all equal. Is it possible to swap a movement and retain the day and date wheels of the old movement?


Thanks for any insights anyone may have.


September 15, 2019 at 11:07 AM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 14020

Markus.

To answer your last couple of questions:


1) Yes all '7A38' movements (however branded) are basically interchangeable, be they pukka Seiko 7A38A, Shimauchi Ltd. V906, Orient J3920, JEPIC Corp. Y19A, Cartier Ferrari Cal. 531, whatever. The only real difference between them is is how their anti-magnetic backplates (and battery +ve terminals) are signed and also the background colour and second languages on their day / date wheels.


2) Yes, it is possible to swap the day / date wheels between movements, but it's a bit fiddly and will also require you to pull and replace all the hands and remove the dial - something best not attempted by a novice tinkerer.


However, as you've stated, you're a 'total newbie', so let's start with the basics. ;)


All Seiko 7Axx movements have a built-in chronograph self test. With the crown pushed fully home, hold the 4 o'clock pusher button in for a good two seconds. All three chronograph hands should rotate through 360 degrees and return to their original starting positions (not necessarily 'Zero').


Next pull out the crown to the first click (setting position). Press each pusher button in turn. This should advance the hands: 2 o'clock moves the 1/10s hand; 4 o'clock moves the sweep second and 10 o'clock moves the 30 minute counter - and thus you should be able to 'Zero' each one.


Do either of those functions work ? :|


September 15, 2019 at 11:43 AM Flag Quote & Reply

My7A
Member
Posts: 4

No they don't. None of the three pushers has any effect what so ever. The 4 o'clock pusher feels like it's almost stuck, it has less travel and for the 2 o'clock pusher it's about the same. The 10 o'clock pusher has a normal feel and travel but pushing it doesn't do anything either. Out of the three small hands the only one that moves is the center one, counting the seconds. The big chronograph hand doesn't move.

September 15, 2019 at 12:21 PM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 14020

OK. So do you have any basic watch tinkering tools ? If not, see this thread. For now, at least, you will need the minimum of a (Jaxa-style) case-back removal tool, a watch case vice, a spring bar removal tool and a watchmaker's screwdriver (set, including one) with a 1.6mm blade.


September 15, 2019 at 12:28 PM Flag Quote & Reply

My7A
Member
Posts: 4

No I don't, but I'll look into that, just not right now, because I'm busy trying to save the world - figuratively speaking. ;)

September 15, 2019 at 12:45 PM Flag Quote & Reply

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