Seiko 7A38 - by the numbers

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Forum Home > Parts Info, Tech Tips and Tinkering > Seiko 7A38 Cannon pinion ( minute hand slips )

donwatch
Member
Posts: 509

Does the 7A38 use a cannon pinion ?   Hand move on when watch is tapped. Info please

February 3, 2014 at 2:05 PM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 9109

'Fraid it does, Don. Although they don't cause problems very often, so there's little or no mention of them on this forum, to date. :(


I did hint at a possible problem with one further down this thread.

There's also a mention I made of them, a couple of years ago, in this post (and other links) on RLT.

To quote myself: Unfortunately, on the 7A38 movement, the equivalent 'centre wheel' is in the middle of the train wheel bridge. 

February 3, 2014 at 2:39 PM Flag Quote & Reply

donwatch
Member
Posts: 509

Thats what I was afraid of--A "seiko system"-----   This mvt runs until it tries to pull date wheel then minute hand stops-also the set position stem turns very easy.

February 3, 2014 at 3:01 PM Flag Quote & Reply

T5AUS
Member
Posts: 18

Right, at the risk of getting sent to stand in the corner for not reading every possible thread before commenting/asking, ( which I think I have done) here goes. :/

My recent purchase of the 7A38-7000 I talked of last week is throwing up a strange fault which I can find no exact reference to on here. It is running and functioning as it should, apart from the previously mentioned date wheel change problem. In the morning when I check what has actually happened overnight I find that the date and day have changed perfectly to the next day ( I never actually see this processes  since I am well gone in the land of nod by then) and the watch is still running fine but it has lost an hour!? This happens every night, quite bizzare, I re set it to the correct time and off it goes on it's merry way accurately keeping time to around 11 pm when I head off to the sack and the next morning exactly the same has happened, it's happily chugging away , the day and date have moved on but it's running an hour late, and sometimes a bit more than an hour, but never over an hour and a half late. I have even left it at that wrong setting just to see if it loses any more time but it never does, always keeping accurate time on that wrong time. So, what could possibly be happening here, the dreaded date wheel surely is not the culprit since it's changing fine, could it be that it's a bit gunked up in the date and day disk area and so drags a bit during the change over. I am reluctant to start unscrewing things until I have really made sure there are no other possible reasons for this behaviour 

Thanks guys

Phil

April 20, 2014 at 6:50 PM Flag Quote & Reply

donwatch
Member
Posts: 509

Phil, try  tap, tapping hard on the side of the case with your finger and see if the minute hand moves ? If it does then I think you have the same problem I have above.  :mad:   And this mostly happens when the gear train is trying to do two things --push the date  wheel and drive the hands :/

April 20, 2014 at 8:34 PM Flag Quote & Reply

T5AUS
Member
Posts: 18

Hi Don

just gave a few sharp taps with my finger and also with the plastic handle of a screw driver  to be sure but no movement at all. :(

April 21, 2014 at 1:20 AM Flag Quote & Reply

Sir Alan
Member
Posts: 451

If you're not sure what is happening and when, I suggest you set the time to 11pm and then observe it. That way you should be able to see whats going on :)

April 21, 2014 at 3:39 AM Flag Quote & Reply

T5AUS
Member
Posts: 18

Lol, so obvious, thanks kind Sir :roll:

April 21, 2014 at 4:48 AM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 9109

Time for me to 'fess up, methinks. 

I have a 7A38 (of sorts) that demonstrates these exact same symptoms and has done so regularly for at least a couple of years.

I suspect some members, who don't understand my enthusiasm for them, are already fed up to the back teeth of me extolling the virtues of the Yema Spationaute III. Well not every example in my collection (a dozen of them) is perfect. Far from it, in this case. :/


The 38mm 'reduced' blue-dialed model # N80A66 is one of the rarer variations. I bought mine off the MWR forum in late 2010 from this FS advert: http://www.mwrforum.net/forums/showthread.php?p=124951 In fact, I paid only $75 for it (I split the lot with another collector who wanted the ana-digi Spationaute - for resale, as it turned out).

 

The watch was a complete mess. It had clearly been buggered about with before. As received, it didn't have one endearing feature. :(

My biggest initial concern was sourcing the correct original screw-down crown for it.

I documented my logistical trials and tribulations (and eventual success) in a long-running thread on RLT, started in November 2010.

I subsequently had the hands re-lumed, although the colour of the 'aged' lume infill wasn't exactly what I'd hoped for.

It was some time after I'd reassembled it (and put it away in my Yema collection box) that I noticed it was losing time.


So, I sat up with it a couple of times, watching the day / date change over (which always worked fine) in the middle of the night. 

It usually lost about half an hour during this period, though even with another watch sat beside it it wasn't easy to see it slowing down.

(The constant seconds hand continues to 'tick' at the same rate as a normal working watch, it is the only the minute hand that slows).

Reason I haven't bothered doing anything with it since is simply that it's a low priority for me, because of the overall general condition.

Were I that bothered about it, I'd simply swap out the movement, because I'm pretty certain the root cause is a slipping cannon pinion.


PS - prompted by this thread I've just got the watch out, moved the hands around to 11:00pm (and thereabouts) and tapped the case.

There is no sign of the minute hand flopping around loose, but there is obviously slippage occuring during the day / date changeover.

So it's clearly very marginal. 


April 21, 2014 at 5:22 AM Flag Quote & Reply

T5AUS
Member
Posts: 18

:D

This one of mine Paul is so rough and I think most would have dumped it ages ago but I do like a challenge and although I really do prefer mechanical watches these particular brand of quartz have won me over. I am not sure if I can justify the time I am spending on it but now that I am hooked there's no going back, will keep you posted :roll:

PS How do I link up to this thread to get email notifications when there are new posts added to it. 

April 21, 2014 at 8:09 AM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 9109

I don't think you can, Phil. :( Webs forum software is pretty basic (minor understatement). :roll:

Just means you'll have to look in on us more a little more frequently (rather than leaving a year between visits), I guess. :P



April 21, 2014 at 10:08 AM Flag Quote & Reply

donwatch
Member
Posts: 509

Paul, I just checked on that NOS Gold 7A38-7280  I just bought and it is hanging up on the second rotation of the date.  Something is slipping  :mad: There was probably a reason for it being mint and un-worn :roll:  I hate to have to R & R the mvt :P Paul, this is why, as a mechanic, I like the 7A28's  ;)

April 21, 2014 at 10:39 AM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 9109

So you've got a second 7A38 demonstrating this same problem, Don ? :o That is unlucky ! :(

The added day / date complication is definitely turning out to be the 'Achilles Heel' of the movement, in more ways that one.

Perhaps that's why Seiko 'beefed up' the later calibers' PCB to cater for the extra current drawn during date changeover. :/

(7A28's use p/n 4001.725 versus 4001.726 for all other 7Axx's).


I guess I've been very lucky in having just that Yema demonstrating the slipping cannon pinion fault (in over 200 7A38's in 5 years).

But then it had obviously been considerably buggered around with previously, by some less than artful watch-botcher. 


I have had another NOS 7A38 which did have serious timekeeping issues though. It was a stainless 7A38-7260 I bought from an Italian seller back in June 2011. That one's hands didn't slip as such. It simply slowed right down - sometimes stopping completely overnight. Luckily, the seller (an authorised dealer) included a Seiko 12 month warranty with it, so Seiko UK serviced it for me free of charge. :D


April 21, 2014 at 11:24 AM Flag Quote & Reply

donwatch
Member
Posts: 509

Too bad you didn't talk to the tech and find out what he did to get it to keep time  :roll: They probably swapped mvt's  :/

April 21, 2014 at 1:23 PM Flag Quote & Reply

T5AUS
Member
Posts: 18

Update, another night has passed and I think we have fixed it, that finger tapping seems to have loosened her up and it was spot on time this morning. However, this does mean there is a bit of dirt floating around in there so I need to get in there and blow it out, maybe remove the day and date disks for a gentle clean. It seems the date wheel is ok but I guess it will need to complete a month of trouble free time keeping to be sure of that. :)


April 21, 2014 at 4:53 PM Flag Quote & Reply

donwatch
Member
Posts: 509

I miss-diagnosed the problem on the gold 7A38-7280: NOT a slipping cannon pinion--- After checking the battery, it's full up, I touched the exposed pivot of the 6 o'clock running second hand with some watch oil. It took off and has been running and changing the day and date. :D  This tells me that there was some dragging friction on the exposed pivot and the oil freed it up and that little step motor can't drive the hands and drive the day wheel while being restrained by friction  :/


April 23, 2014 at 10:57 PM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 9109

Well Don, despite yours and Phil's 'lucky fixes' I can assure you that the 'slipping cannon pinion' problem exists. You remember I wrote that my 38mm blue dialed Spationaute III had previously been exhibiting the symptoms - losing approximately half an hour per night. Since I got it out again it's got much worse. :( The last two nights, the hour and minute hands stopped moving at 00:50am - around the time the movement starts to engage the day wheel, after having successfully flicked over the date. Yet the (time) constant seconds hand is still merrily ticking away in the morning. When you pull out the crown to wind the hands on (8 hours or so) to the correct time, everything feels normal. Indeed, the watch appears to keep good time to around midnight. I think a movement swap is well overdue.


April 24, 2014 at 5:26 AM Flag Quote & Reply

T5AUS
Member
Posts: 18

Interesting Don, I have now discovered that mine resorts back to losing about half an hour on the day date change if I have the chrono engaged, with the chrono off she is fine every time and doesn't loose a beat on the change over. :roll: 

April 27, 2014 at 4:59 PM Flag Quote & Reply

donwatch
Member
Posts: 509

OK-- now I'll engage the chrono and see what happens  :/

April 27, 2014 at 5:20 PM Flag Quote & Reply

donwatch
Member
Posts: 509

Yesterday I engaged the chrono on all of my 7a38's and this morning all were on time and had correctly changed day and date :D

April 28, 2014 at 11:23 AM Flag Quote & Reply

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