Seiko 7A38 - by the numbers

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Forum Home > 7Txx General Discussion Area > The Seiko 7Txx series movements - expendable or repairable ?

Seiko7A38
Site Owner
Posts: 10936

Whereas the Seiko 7Txx series of chrono's offer a vast variety of different dial and case styles, and in some cases additional features, their percieved 'lower quality less-well-engineered' movements, with a higher proportion of plastic components seem generally unloved.


Back in the first week of March, John asked this question at the end of his post, in the C'mon - Show us your 7T59 thread:

What's the quality of the movement like in these Paul, is it of similar quality to the 7Axx's or are they in a different league?


My reply was naturally 7Axx biased - not particularly factual nor helpful; I was more concerned about making a wordplay:

That's the 'gotcher' John. Compared to the 7Axx movements, 7Txx movements are very much Second Division, IMHO.


Simon posted a more factual reply in a thread on RLT yesterday: http://www.thewatchforum.co.uk/index.php?showtopic=74526

I've been 'playing' with 7T32's, 7T34's and 7T59's recently. 

In my opinion, the movements are NOT serviceable unless you are an expert (which I'm not).


But does anybody actually bother repairing them ? Particulary as most 7Txx movements can still be bought NOS for $50 - $75.

I'm sure I'd seen a video of someone doing a strip and re-build of a 7Txx movement on YouTube.

It wasn't this one: http://www.youtube.com/watch?v=UyCCTrM2TEI - it possibly had classical rather than a jazz backing track.

Does anyone know the video I'm referring to ? Because, now I'm actually looking for it, I can't find it again. :/

March 30, 2012 at 4:03 PM Flag Quote & Reply

Sir Alan
Member
Posts: 456

I've been on a rapid learning curve since the beginning of the year, starting with a complete disassembly of a 7A38 movement (that was dead - honest!!), an attempted partial re-build of a 2nd 7A38 movement that was missing the day/date complication, which while successful in part (I did get the complication fully working), I ending up scrapping as the watch was keeping terrible time (but see below). 


I then had a lot more success on a 7T34, removing a dead movement and re-fitting a new movement I'd purchased. This was a complete success, I love the watch and feel a real affinity with it. :P

 

After this re-fit, I took the dead 7T34 movement completely apart - everything!!!

 

I did this carefully (as I had done the 7A38) thinking that any of the parts I removed might be useful in the future.

 

A couple of observations:

 

1) The 7T34 movement (like the dead 7T32 which I have also subsequently disassembled) is held together with some metal screws like the 7A38, but is 'mostly' clipped together. The layers being made of either plastic, or very thin metal sheet.


This means that it is very difficult to put back together as these layers deform very easily due to their thickness.


Almost all of the gearing is in a single layer sandwiched between all plastic components. I was surprised that the majority of gear wheels are metal (not plastic), but there are no jewels (so the bearings are plastic). These gear wheels are tiny and multi-layered (i.e. gear wheels on top of gear wheels).


I guarantee that you could not put the plastic plate/bridge back on top of all these gears once it has been removed - there are simply too many to line up with their corresponding hole. :roll:

 

I have bought six 7T34 watches, three of which have dead movements. In all three the circuit is dead (corrosion / rust / battery acid damage). Since the 7T34 movement seems to be easily available to buy (at the moment) I haven't even contemplated trying a repair of any kind.


2) The 7A38 movement (as Paul and many others have noted) is a completely different beast. It has been designed not only from the highest quality components, but to be fully serviceable.

 

I have done (following my two experiments above) the following repairs - all 100% successful.

 

1) replace the circuit in what was a dead watch. I used the circuit from my experimental watch (the one I fixed the day/date complication on). This was a simple procedure and worked first time. I'm really pleased because the case, bracelet, dial and movement are all very clean, so I've got a tip top watch for not a lot of money.


2) replace the main chrono second hand shaft (with gear wheel attached) on a watch that came without a chrono second hand.

 

I should have spotted this in the ebay listing but didn't. I'm learning ALL the lessons here!! :mad:


At first I assumed the hand was simply missing, but my attempts to fit a replacement failed. The hand just wouldn't attach. I could see the shaft and was a bit puzzled. But when I took the bridge off (this is the simplest to do as it only requires removing the little finger spring and two other screws) and removed the shaft, I found the problem. It was about 1mm short, missing the end part  :roll:

 

Anyway - I went to my spares container (remember I kept them all carefuly), got out the part I needed, compared them, re-fitted it, re-attached the hands and .... bingo. I've got a watch with ALL the functions it should have (and the hands align nicely on the marks!!) :D

 

3) this one is embarrassing, but I'll confess to it.  Fix a watch I broke:mad:

 

I recently got a lovely example of a 7A38, and immediately fitted a new crystal. But .......... because I had been also doing a lot of work on 7T34's, and because I wasn't concentrating and I guess it was about time I made a mistake to bring me down to earth, when I went to remove the crown it picked the wrong hole to push the crown release lever.


Well, because it was the wrong hole (and I bet some of you can guess which hole I picked), pushing around in there didn't release the crown - well, it wouldn't, would it!!

 

So, I gave it a good old waggle and push and only after a couple of these did I realise my mistake. Ohhhh NOOOOOOOOOOOO.

 

Well, I thought I'd got away with it - the second hand was still ticking away merrily.

 

But, when I put the movement back in the case I realised I'd killed the main hands dead - no chrono second hand movement, no hour or minute movement.


I've just killed a lovely watch. :(


I took the movement out, and used my loupe to look into the wrong hole I'd been poking around in. And of course, partially visible was a gear wheel.


Well, given that I'd killed it, I decided that I might as well try and fix it. I had nothing to lose (except more pride, and that was feeling pretty low at this point).

 

To fix it required taking a lot more apart than in 2) above. But, as I'd done a full disassembly before (but not a re-assembly) I knew roughly how to do this.


To get to the gear required removing everything to expose the coils and the three bridges. The main bridge has three jewels and is fixed by three screws. Removing these allowed me to get to the gear, and lo and behold, I'd managed to knock off two of the teeth, so it wasn't engaging anymore.


So, off to my spares container, find the same part (and I only did this by visually comparing the two parts) and then back in with the new part.

 

Now - I can't quite remember the absolute details here, but I remember that there were 3 gears, offset and overlapping each other, with the biggest one being the one I was replacing. The tricky part was getting the bridge back on, because there were several shafts that all had to line up with their corresponding pivot hole or jewel in the bridge.

 

What I did was to practice this operation on my 2nd spare movement (the one I hadn't disassembled fully) - it wasn't easy at all, but I worked out a way to do it by turning the crown (to get the gears to engage and turn) and then to wiggle the bridge gently with my finger feeling when it wanted to full sit down.


Well - I did it. 8)


I put the watch back together and it works perfectly, keeping perfect time. RESULT :-)


But I did learn another big lesson here. TAKE CARE when poking things into holes in the movement.


Now - this operation isn't easy. When I tried to put the practice movement together, I got it wrong, tightened the screw of the bridge and , CRACK, the main jewel shattered and that was the bridge dead.


I tell this story because the 7A38 can be fully worked on, even by someone like me (eyesight not great, patience - average). You could NOT do this type of operation on a 7T34 or 7T32 movement.


I'm building up a nice parts spares holding and all of them are likely to be useful at some time or other.

 

 

March 30, 2012 at 6:26 PM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 10936

Thanks for that comprehensive reply, Simon. It's exactly what I was hoping to prompt by my question. :)


It seems that Seiko US (Coserv) do support and repair 7T32s, or have done in the past, though whether they repair to component level or by simply swapping out movements, we cannot know. Before I made the first post, I had done some googling, naturally. ;)


http://forums.watchuseek.com/f21/fixing-up-seiko-7t32-chrono-112449.html

I'm a big fan of the 7T32 and have had several repaired through Seiko (Coserv, in Mahwah NJ) and it ran about $80 plus shipping. They usually repaired/replaced the movement ....


Others appear to be of the same opinion as you and I:

http://www.sg-roc.com/threads/33250-Seiko-7T32-Movement-Repair

Hmm bro,i'm afraid there's no watchmaker who wants to fix a 7T32 movt.


March 30, 2012 at 11:25 PM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 10936

Slightly off topic, but reference this part of your post:

 

2) replace the main chrono second hand shaft (with gear wheel attached) on a watch that came without a chrono second hand.

I should have spotted this in the ebay listing but didn't. I'm learning ALL the lessons here!!

 

At first I assumed the hand was simply missing, but my attempts to fit a replacement failed. The hand just wouldn't attach. I could see the shaft and was a bit puzzled. But when I took the bridge off (this is the simplest to do as it only requires removing the little finger spring and two other screws) and removed the shaft, I found the problem. It was about 1mm short, missing the end part

Anyway - I went to my spares container (remember I kept them all carefuly), got out the part I needed, compared them ....


Be careful of not getting your parts mixed up.

The shaft on the 7A28's Chrono Centre Seconds Gear Wheel will be 1.00mm shorter than that of the 7A38's - for obvious reasons.

Seiko part numbers are 888.725 (7A28A) vs p/n 888.731 (7A38A). Here are a couple of photos I've taken of the latter at various times:





At 4.50mm Ø this 60T gear wheel is the biggest in a 7Axx movement. As Simon can confirm, the wheels in a 7Txx are rather smaller.

March 30, 2012 at 11:36 PM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 10936

If anybody fancies having a 'play around' at fixing Seiko 7Txx movements, I see UK seller 'nomishtims' has just listed a load on eBay:


http://www.ebay.co.uk/sch/m.html?_nkw=Seiko+7T*&_sacat=0&_odkw=&_ipg=50&_sop=12&_osacat=0&_ssn=nomishtims

June 14, 2012 at 3:32 PM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 10936

It would seem nobody did (fancy having a play), and the seller may have had a go himself - meeting with a similar lack of success. :(


http://www.ebay.co.uk/itm/370698003958


4 x 7T59B Seiko Quartz Chronograph Watch Movements for Spare Parts or Repair

 

Three of the movements are in good cosmetic condition. One show signs of water damage/rust. I do not have the skills or knowledge to test them, so I am selling them as faulty - for spares or repairs.

 

The four movements have been partially dismantled and are contained in plastic zip-lock bags as pictured. All of the major parts appear to be present but some small parts (e.g. gears, screws, etc.) may be missing.

 

Suitable as a source of hard to find genuine Seiko spare parts, such as coils, circuit boards, gearwheels, etc. ....


In fact, if you click on the link in my previous post (which still works), there seems to be a common denominator: 'Faulty' and 7Txx. 


November 28, 2012 at 1:16 PM Flag Quote & Reply

rdwiow
Member
Posts: 6

I bought some of these packs some years back when they were only a couple of quid.

They have been a valuable source of circuits and coils over the years.

The 7T series circuit does seem to suffer from battery electrolyte corrosion more than others due to the flex circuit going down the battery contact and under the battery. This makes it very easy for the leakage to track back up and corrode the circuit.

They are also prone the the circuit contact breaking off the flex circuit, particularly the stop/start contact is a favourite to break off.

These were sadly never in the same league as the old 7A faithful.

November 30, 2012 at 4:21 PM Flag Quote & Reply

ric

Posts: 44

you can ways buy a duff movements east of London. :D

May 9, 2013 at 4:47 PM Flag Quote & Reply

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