Seiko 7A38 - by the numbers

No you didn't mis-read the title - I'm working on a 7A48 for a change. Specifically a well-worn 7A48-7000 belonging to a chap at work. He's owned it from new; a present from his wife. I'd stopped and chatted briefly with him, last year, when I'd observed him wearing it.

More recently I noticed him sporting a modern-looking stainless / black-dialed 7T92 chrono' - so I enquired as to the fate of his 7A48.

The Z-fold clasp had finally given up the ghost - metal fatigue. So I said I'd have a go at repairing it for him.

Apart from the broken clasp, the bracelet itself is badly stretched; the crystal scratched, battery dead flat and chrono' buttons sticky.

Steve said that some of the chrono' functions hadn't worked in a while. So it'll be an interesting exercise to see what I can do with it.

The 7A48A movement inside was surprisingly virtually spotless. Here it is, reassembled in the watch case, after I'd given that a good clean up; stripping, cleaning and greasing the pushers as a matter of course. New battery fitted, and almost everything worked ....

That was apart from the 30 minute counting subdial, which was as dead as the proverbial dodo. 

So, although it was technically outside my remit (which had been to replace the clasp), I decided to have a go at fixing it.

Simplest, quickest and dirtiest solution ? Try fitting a known good (secondhand) coil in place of the existing one. Right ? 

Which I did - to no avail. Still not so much as a flicker of life from it. So I popped the movement back out of the case.

Oddly enough, when I'd done this the first time I'd gently nudged the the 1/10s and sweep second chrono' hands around to 'Zero', with the point of a wooden cocktail stick. Perfectly safe to do.  But as the 30 minute counting hand was already zero'd - I hadn't bothered moving it before. I replaced the battery and crown, to see if I could give it a little nudge to get it started, but it was absolutely solid. 

Much as I don't like dismantling bridges (on my own watches, let alone someone else's) I decided to delve deeper into the problem.

The 30 minute chrono' bridge is relatively simple and easy to get at - but also involves removing the centre seconds bridge:

The culprit responsible for jamming this part of the movement solid is just visible at the bottom of the photo. 

It's tiny; not particularly easy to photograph on its own. Nor a fault I've ever personally encountered before.

A chunk of the magnetic ferrite core had broken off the step rotor, and was firmly stuck to the gear teeth. 

It's at times like these, when those partially stripped irredeemable gash 7Axx movements you'd forgotten about, come in very handy. 

That little step rotor cleaned up very nicely and after a cup of coffee and cigarette to steady my nerves, the bridges were replaced:

But having taken that photo, abject panic set in for a few minutes - hence the frantic phone call to Simon, to ask his advice. 

This was actually the first 7A48 that I had ever dismantled. I had a horrible feeling I might have inadvertantly lost something. 

If you've worked on 7A38's and referred to the manual, then you'll be familiar with this exploded diagram at the top of page 7:

It's that little gear wheel labelled (65) 1st calender correction transmit wheel. You'll note it's missing from my photo in the previous post.

When working on 7A38's, if you have removed the green plastic 710 spacer and subsequently been foolhardy enough to withdraw the crown stem (which is all that holds it in place), it is all too easy to lose this little gear wheel - particularly if you you suffer momentary brain fade and turn the movement upside down. Been there (only once or twice, honestly readers); done that - got the T-shirt. 

Question is: should the 7A48A movement have one (and I've presumably lost it) - more to the point does it need it for full functionality ?

Problem lies in correctly identifying it from the Seiko parts list, because it isn't described as '1st Calender Correction Transmit wheel'.

Here are a few possible likely candidates From the Cal. 7A38A parts list:

281.725 Setting Wheel 

282.728 Clutch Wheel

962.726 Intermediate wheel for calendar cerrection correction

962.727 Additional intermediate wheel for calendar correction

Next step was to look up the Cal. 7A48A parts list - the first two of those part numbers are listed - but not the latter two.

Instead, there is a part number 962.725 listed, described as 'Intermediate wheel for calendar corrector'. Hmm. Interesting. 

Here's one of Simon's super hi-res photos of that gear taken from the dial side of a 7A38A movement, borrowed from another thread:

Undeterred (and fully prepared to strip it down again, and replace said 'missing' gear wheel), I reassembled the watch - re-using the original 30 minute counting coil which I'd suspected of being faulty (but not bothered testing). Full chronograph fuctionality restored.

You'll notice the 30 minute and sweep second hands are slightly off their marks. That's simply because I'd left them on the ends of their spindles while I was messing about with their bridges, so I might be an odd tooth out, either way. I'll re-fit them properly later.

Having fixed the chrono' problem, I was now more concerned about date / moonphase setting. Pulling out the crown to the first click,

I can quickset both the date pointer and the moonphase. Pulling the crown out to the second click and manually turning the hands through twenty-four hours (a good few times), both the date pointer and moon phase advance. So am I actually missing anything ?

Belated Footnote: If in doubt refer to the manual. 

Those of you who've used the Seiko 7Axx technical manuals may already know that you should for example read the 7A38A manual in conjunction with the 7A28A manual. There are sections in the latter which are applicable to all 7Axx calibers. The same applies to the 7A48A manual. It's even shorter than the 7A38A manual, comprising only 3 pages and states on the last page:

The explanation here is only for the particular points of Cal. 7A48A.

Refer to the Technical Guide 7A28A and the Techical Guide, General Instruction for SEIKO Analogue Quartz for instruction.

Note it does NOT say to also refer to the Cal 7A38A manual, as I had done. 

Page 2 of the 7A48A Technical Guide primarily covers calendar and moonphase operation. It includes this small diagram:

While not particularly clear (nor helpful), it becomes obvious that the 7A48 date corrector wheel set-up is different to that of the 7A38.

I'm pleased to say that although I'd manually wound it forward (several times) and hence had a good idea that it would anyway ....

the watch's date pointer changed automatically by itself last night. So obviously there aren't any gears 'missing'. Panic over. 

My last photo showed how badly scratched the original crystal was, so I just had to change it. The OEM Seiko crystal, part number 320W42GN00 is obsolete and NLA, but of course there's always the Sternkreuz equivalent, p/n XMF320.927 - which, had it been my own watch, I probably would have fitted. But the watch's owner had said not to go to any great expense, so instead I fitted a Cousins 32.0mm Ø X 1.5mm 'cheapie', with the polished chamfered bevel edge upwards. While not as sharp as the ground bevel edge on the original Seiko crystal (or the Sternkreuz), it looks the part and made a great improvement - as fitting any new crystal usually does:

In the meantime, having soaked overnight in neat 'Flash' cleaning fluid, followed by three 10 minute cycles in the ultrasonic tank, the bracelet had since been relieved of two and a half decades worth of solidified 'wrist cheese' and all evidence of the owner's DNA. 

I knew it was badly stretched before I started cleaning out all the muck from between the links, but now actually being able to see how badly the small interconnecting link sections are worn, I'm beginning to wonder about the wisdom of fitting a new (secondhand) clasp.

If I do, I think the next thing to break (soon after) will be the bracelet itself. Anybody got a spare p/n Z1093C bracelet going cheap ? 

On Monday, I asked the watch's owner what he planned to do with the watch, once he got it back. He said he'd go back to wearing it regularly, because he wasn't too keen on his new 7T92. I explained to him the fragile state of his original bracelet, and the distinct probability of it breaking again in the near future, unless he was exceedingly careful with it. He said that he'd like to keep it original.

I suspect the chances of finding another Z1093C bracelet are pretty slim to none. I'm not normally an advocate of fitting non-original replacement bracelets to Seiko 7Axx's - even other people's. But I started rummaging through my various boxes to see if I could find anything which might fit. The 7A48-7000 is a bit of an odd one. The lug engs are 23mm wide, but the boxed lug width is only 18mm. 

This is the best match I've managed to come up with so far. It's an all-stainless Orient solid link bracelet - 18mm lug width fitting, 23mm at the shoulder with slightly rounded profile link sections. It came fitted to my Orient J39725-70 'Panda' beater. Or at least one end was attached. It clearly wasn't the original bracelet for that watch (20mm lug fitting). I robbed the clasp off it for use on another Orient J39.

That looks great Paul!!!

You do awesome work. I wish you weren't so far away-I could keep you busy with my collection for ages 

Remember this ? 

At the time, I debated whether to re-brush the top and polish the sides of the watch case. Apart from a few scrapes and dings, the bezel's gold plating was also well worn, so to my mind, it wouldn't have looked right with a re-finished case. Besides the used Orient bracelet which I'd fitted nicely matched the level of accumulated wabi - and I thought the owner would prefer to keep the 'used' look.

I'm glad I didn't bother now.  This weekend I've got it back in for a bit of remedial work. 

The owner, Steve, had taken to wearing it again daily, as he much preferred it to his new 7T92.

He took it away on holiday with him last week and 'fell down a bank and banged it on an iron bar'.

I refrained from asking him whether the consumption of copious amounts of alcohol had contributed to his (and the watch's) downfall. 

He told me that it had stopped working altogether. But a quick play with the buttons proved that everything still appeared to be O.K.

I reset the time by the atomic clock on Friday, not long after he sheepishly handed it over and it hasn't lost a second since. 

Chrono' operation is fine. I've just advanced the sweep hand a little out of harm's way (viz. the gaping hole in the crystal).

The black fibres, all over the dial, have come from the inside lining / cushion of the Seiko box belonging to his 7T92.

320W42GN00 is obsolete and NLA, but of course there's always the Sternkreuz equivalent, p/n XMF320.927 - which, had it been my own watch, I probably would have fitted. But the watch's owner had said not to go to any great expense, so instead I fitted a Cousins 32.0mm Ø X 1.5mm 'cheapie', with the polished chamfered bevel edge upwards. While not as sharp as the ground bevel edge on the original Seiko crystal (or the Sternkreuz), it looks the part and made a great improvement - as fitting any new crystal usually does.

Question is, this time shall I fit a Sternkreuz MSM320 (straight-sided) crystal or a bevelled edge XMF320.927 as a replacement ? 

It would be the bevel for me 

Me, too Simon. However, I'm mindful of this: 'But the watch's owner had said not to go to any great expense ....'

And as it's already fitted with a non-original bracelet, would he worry about the lack of a fancy bevelled edge crystal ? 

Besides, I'm thinking that a Sternkreuz MSM320, pressed down flush with the top edge of the bezel might be a little more 'bullet-proof'.

Anyway, rather than just do a UDI, and fit a Sternkreuz MSM320, I thought I'd ask the question.  I told Steve the difference in prices between the two crystals - £1.50 versus about a Fiver (with VAT) for the XMF320.927. He surprised me by saying he'd go for the latter. Got home, checked my crystal stock and found I didn't actually have one - I'd used the last in my ex-Okazii gold-tone 7A38-706A. 

Needed to order a few bits from Cousins anyway. When the package arrived, this Sternkreuz p/n XMF320.927 didn't have quite such a large polished bevel edge as previous ones I bought. Which reinforces what Lawrence wrote in the Crystals & Gaskets thread recently:

Aftermarket crystals "are like a box of chocolates, you never know what you 'gun get"

This morning I decided to tackle the job. Surprisingly the Cousins 'cheapie' replacement crystal I'd fitted previously came out cleanly.

I'd expected it to shatter as I pressed it out. But the inside of the watch case was already full of minute particles of powdered glass - all over the dial, Tachymeter ring, all round the '710' spacer and the threads of the watch case. Took me ages to clean up with Rodico. 

Here's the dial after my second clean-up pass with Rodico. You can still see odd bits of glass glinting, but also in a couple of places, the splintered glass had scratched the dial paint (exposing the bare metal underneath) - like under '17' on the calender scale.*

Notice the sweep second hand had been knocked off it's mark. It was also bent in two planes:

*Also a little scratch in the dial paint between 52 and 53 on the minute scale - directly beneath the point of impact. 

Popped the sweep hand off, rolled it flat; stroked it back into shape and re-fitted it. Yes - I could have used a replacement hand, but ....

So here it is ready to do battle once again. Note the very small polished bevelled edge on this particular Sternkreuz XMF320.927.

Incidentally, when Steve first told me the watch had stopped working after the accidental impact, I was already thinking displaced main (central hand stack) jewel, or that the movement might possibly jammed up by glass fragments. As I didn't really fancy doing a full 7A48 movement strip and re-build, I started looking for a 'beater' to use as a movement donor.

This was one of two I'd put on my eBay watch list:

http://www.ebay.co.uk/itm/281158736928

Just as well we didn't need it in the end, eh ?