Seiko 7A38 - by the numbers

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Forum Home > Bend it, Mend it - Mods & Wreckers > Probably the easiest chronograph fault fix, ever - unless you know different.

Seiko7A38
Site Owner
Posts: 9119

I recently bought a Yema N8 OP896 'Pseudo Plongeur' from Korean eBay seller smith_speaks (previous eBay ID Kwonbax). 


http://www.ebay.co.uk/itm/301143006456



I really didn't need another one, but as Don had had second thoughts and withdrawn his bid, I thought I'd stick in a bid for the minimum amount - and won it. :) I've already got a nice example of the white dialed version in my collection, but this one was slightly different in that it had the 'minimal printing' dial, with just YEMA (no PARIS or QUARTZ, like my other one) so I could almost justify it to myself. :P

It's in nearly NOS unworn condition, slightly grubby (it has since cleaned up well) but the seller described it as faulty:


Seller notes: “Very Clean Condition / Working and keeps good time / Chronograph function needs fixing”


- Working Condition, Keeps good time, but chronograph function didn't work right,

- Once stopwatch starts, center second moves, but when it stops, it didn't flyback,

- Other Seconds works fine, and time tells good


It arrived on Tuesday. I posted a less-than-flattering Q&D wrist shot in the WRUW thread and cockily wrote underneath it:


The fault with the chrono' sweep hand (reset), described by the eBay seller in his listing, should be the easiest to fix, ever. :D


April 17, 2014 at 6:59 AM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 9119

As received, the chronograph 'fault' symptoms were slightly different to how the seller had described them.


Pressing the 2 o'clock 'start' pusher, the chronograph functioned perfectly and stopped accordingly. However, when you pushed the 4 o'clock 'reset' (or 'flyback' as the seller referred to it) pusher, nothing happened. Pulling out the crown to the second click would reset all the hands (but not neccessarily to zero - only where they had stopped previously). The 'hold in the 4 o'clock pusher for 2 seconds' in-built self test did not work either. Pulling out the crown to the first click allowed you to reset the 1/10s and 30 minute counters, but again repeatedly pressing the 4 o'clock pusher, in any attempt to move the chronograph sweep hand, had no effect whatsoever. :(

Yet all three pushers had a really nice like new 'clicky' feel to them.

But I had a pretty good idea what the problem was. 8)


April 17, 2014 at 7:35 AM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 9119

Here's the Shimauchi Ltd. V906 signed 7A38 movement - nice and clean, fitted with a new Renata #394 battery (by the seller).

No sign of prior battery acid damage or moisture ingress. :)



I took the dial / movement out of the case; re-inserted the crown stem and operated the chronograph functions using a screwdriver tip on the cams of the switch levers and everything worked just as it should, first time, including the 'reset' and 'self-test'. Hey Presto. 



April 17, 2014 at 7:48 AM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 9119

You see I've been here once before. ;) My very first Yema N8 OP896 (the black dialed one) demonstrated the same symptoms. :/

It's not so much a 'chronograph fault' as a 'design / manufacturing fault' with this particular quirky little Yema N8 'Pseudo Plongeur'.

The watch case is asymetric with a prominent bulge on the right hand side, between the two pushers:




Note the uneven gap around the 4 o'clock pusher   in the eBay seller's photo.

Yema N8's differ from Seiko 7A's in that their pusher assemblies are 'press in'. Unfortunately, they're not always pressed in straight. :roll:

So here's what I also found when I unscrewed the case-back:




That's the 4 o'clock 'reset' pusher. :o Although the pusher shaft was contacting the cam of the switch lever and indeed partially acting on it, it wasn't moving it enough to make a connection with the switch's respective contact post embedded in the '710' insulator spacer.


April 17, 2014 at 8:09 AM Flag Quote & Reply

PHK
Member
Posts: 224

Now that is piss-poor engineering! Eagerly awaiting your fix. 

I see why we have no French cars over here.

PK 8)

April 17, 2014 at 9:10 AM Flag Quote & Reply

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