Seiko 7A38 - by the numbers

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Forum Home > Parts Info, Tech Tips and Tinkering > 7A28a PCB? source?

MrJones
Member
Posts: 3

Hello all,

I found my way to your excellent site as I've been servicing one of the RAF Seiko Gen 1 chronographs.

I serviced the movement on Friday, overall it seemed clean but there was a curiously large amount of sticky oil or grease residue between the dial and top plate and also some minor battery leak corrosion (but this seemed mainly confined to the plastic movement spacer) and the negative battery connection piece had some loss of the gold plating.

 All the coil blocks seemed clean and overall all the metal parts were fine - I've cleaned them, reassembled and reoiled according to the service instructions.The train is free but the watch seems totally dead - I don't get any current consumption reading on a multi-meter when I test in the way described in the manual.

So I'm guessing the PCB is the most likely fault. I've looked everywhere I could think of (Cousins / Gleeve & Co / Ofrei / Jules Borel / Boley / ebay) and I can't find anyone with the PCB for sale.

I was wondering if anyone would be prepared to sell me a working PCB / point me in the right direction.

Or are there other things I could test in order to identify whether the PCB is the faulty component? I mostly service mechanical watches, so could quite easily have missed something obvious.

Many thanks in advance for any advice! I attach a couple of images - the first showing the oil etc and the second showing the small extent of the corrosion.

Crispin Jones


October 16, 2016 at 8:38 AM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 12370

Hello, Crispin - and welcome to the forum.

It would have been interesting to see a close-up photo of the removed PCB.

Those blue suphate deposits on the negative battery terminal in your photo look familiar.

This was a Yema N8 (French-built Seiko 7A38 equivalent) I encountered a few years ago - more detail in this thread.




As I wrote at the time:

Damage to the PCB appeared to be minimal, other than some loss of gold plating to the negative terminal contact ....

Reassembled it - popped in a new Renata # 394 battery - result ? Dead as a bloody dodo !! :mad:


Yet other battery acid damaged PCB's, including one that came out of a severely corroded Orient J3920 movement did work ! :roll:


 

If you'd taken some time to browse the topics in the other part of the Workshop section, you'd have found numerous other examples, including this thread, which also concerns a 7A28-7120 RAF Gen. 1 with localized battery acid damage to the PCB.




As far as sourcing a replacement PCB goes, as you've discovered, supplies appear to have dried up. :(

I'd suggest that your best course of action would be to purchase a working 'beater' donor 7A28. The gold-tone 7A28-7029 is cheap and plentiful (in the USA) and most folk's favourite choice. Those YSL TD-780's (with the Shimauchi V905 branded movement) can also prove to be a cheap 7A28 movement source - as indeed might a Yema N7.


However, although the 7A28A movement parts list calls up Seiko p/n 4001.725, I believe there's no reason why you couldn't use a p/n 4001.726 - a slightly uprated version used in the Seiko 7A34, 7A38 and 7A48 (and all the associated re-branded movements). ;)


October 18, 2016 at 6:44 AM Flag Quote & Reply

MrJones
Member
Posts: 3

hmm interesting, I've removed the PCB again just now, there are some very small corrosion marks etc.

Do you have any thoughts on why the PCB's die from the battery leakage? I continuity tested it and all seems fine on this front, also cleaned up the contacts but still completely dead...

Will start looking for a donor watch, thanks for the tips!



October 18, 2016 at 10:26 AM Flag Quote & Reply

MrJones
Member
Posts: 3

closeup of the PCB showing the very minimal damage from the leakage (at least to my eyes it looks quite clean)


October 18, 2016 at 10:29 AM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 12370

Not really - I presume it's down to an increased resistance or worst case a broken track / short circuit (invisible to the naked eye). :(

There's also the 'Murphy's Law' factor. Those PCB's, like yours, which clean up well, that you'd expect to work - and frustratingly don't; whereas some others which appear hopelessly damaged miraculously still do. :roll:

Plenty of examples in this thread: http://www.seiko7a38.com/apps/forums/topics/show/7517616-inside-the-7a38 (scroll down).


October 18, 2016 at 10:38 AM Flag Quote & Reply

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