Seiko 7A38 - by the numbers



Post Reply
Forum Home > Parts Info, Tech Tips and Tinkering > Sticky: How to set the Day / Date on a Seiko 7A38 - and when NOT to do it

Site Owner
Posts: 12808

A pretty basic question really - and one I'd expected might have been asked in this thread in the main 7Axx General Discussion area:

But if you don't have a copy of the Seiko 7A38 instruction manual and haven't managed to find an online .pdf version .... (a link is included on our 'Other Links' page) .... You might well ask. 

This morning, with my 'Admin' hat on, I ran my usual daily check on incoming google searches - and noticed this one in particular:

how to set day date on seiko 7a38 Try it yourself: Google search (Belated edit: this topic is now the first result returned).

The visitor from Larbert in Scotland certainly had a good look around the forum, but I'm not convinced he found the answer he sought.

It is of course on page 4 of the Seiko 7A38 instruction manual (and hopefully common knowledge to everyone on this forum):

January 24, 2013 at 10:13 AM Flag Quote & Reply

Site Owner
Posts: 12808

However, the 'Note' at the bottom of the page should probably include a stronger warning:

Rather than merely stating: 'the calendar will not change to the next date' ....

Perhaps it ought to read: the auto day change-over might never work again ! 

You can of course change the day / date (as on any watch) by advancing the hands through 24 hours (or more) by turning the crown.

But the Seiko 7A38 has a 'quickset' day / date feature - as shown on page 4 of the instruction manual. It's one of the more modern features that those of us who love these watches appreciate. It is also the watch's Achilles Heel. If you read on the 'Net elsewhere about Seiko 7Axx's, you'll sometimes see the phrase 'All Metal Gear Train' touted. I've used it myself in eBay listing descriptions. 

It's not strictly true. There is one plastic gear in a 7A38 - the Day / Date driving wheel (Seiko part  # 867.725). It is the weakest link.

January 24, 2013 at 11:26 AM Flag Quote & Reply

Site Owner
Posts: 12808

Here's a few of Simon's photos, showing the day / date wheel, which I've borrowed from another thread. I'm sure he won't mind. ;)

January 24, 2013 at 11:56 AM Flag Quote & Reply

Site Owner
Posts: 12808

It's not just the fact that it's plastic (it can be moulded in either white or black), and that it is perilously thin in a couple of places ....

But also it's position relative to the battery (on the other side of the movement) which makes it potentially even more vulnerable. 

Here's one of my own photos showing the teeth of a white plastic day / date driving gear underneath the main-plate battery recess:

Here's another of Simon's photos (borrowed from another thread):

So any prolonged leakage of either fluid or fumes from an old run-down battery could also easily weaken it further, by making it brittle.

January 24, 2013 at 12:30 PM Flag Quote & Reply

Site Owner
Posts: 12808

The Seiko manual states: If the setting of the calendar is made when the hands are pointing between 9 P.M. and 3 A.M. ....

Whenever I've observed them, the day / date changeover sequence of my 7A38's goes as follows:

11:00 PM Date wheel starts to move and is usually completed by 00:30 AM (the following day).

01:00 AM (previous) Day starts to move. By 01:30 AM changed to 'alternate' language; by 02:30 AM the Day changeover is complete.

I'm not entirely certain how it works (it's obviously not possible to see with the day and date display wheels in place), but those two thin lever arms on the plastic day / date driving wheel engage the teeth on their respective wheels during this change-over period. Thus common sense would tell you not to mess wiith the day / date settings, using the crown's quickset mechanism between these times.

But people do make that mistake. I've done it myself once - and only once. Never again. I've also bought two 7A38's where the seller had obviously broken the day / date driving wheel in this manner - most recently my NOS Orient J39908-70, the subject of this thread:

Thankfully, one of the topics read by our erstwhile visitor from Larbert was that one - which includes the salutory warning:

Rule #1 when setting 7A38's - NEVER mess with the day / date quickchange between 11:00pm and 3:00am.

He read it 3 times - so hopefully he got the message, if not the instructions on how to actually go about it.

One other little tip: If you buy a 7A38 with a flat battery (often a gamble in itself), or if you've left one for a long time, in a collection box or drawer, and the battery has run out, particularly if the day / date windows are fully aligned (regardless of the language shown) and the time is shown between 9:00 and 3:00 - you don't actually know where it stopped. I've found that 7A38's batteries will often expire after midnight, as the watch draws slightly more current while it's doing the day / date change-over. Once you've fitted a new battery, pull the crown out to the second click, and rotate the hands through at least 12 or possibly 24 hours, so that you are absolutely sure what time it is displaying: say 1:30pm rather than 1:30am. If you 'over-shoot' - wind it on manually another 12 hours, just to be safe.

Once you're out of the 11:00pm to 03:00am 'danger zone', it takes only a matter of seconds to reset the day / date using the quickset.

It takes rather longer to remove the movement; pull the hands; remove the dial and day / date wheels to replace a broken drive gear.

You know it makes sense. ;)

January 24, 2013 at 1:06 PM Flag Quote & Reply

Site Owner
Posts: 12808

Funnily enough, at the weekend I had to refer to the Seiko 7A48A Technical manual - probably the first time I'd read it properly. 

Top of the last page is this warning:

Yet no such warning appears in the 7A38A Technical manual, where it's really needed.

What makes this warning seem more pointless and misplaced is that the date driving gears in a 7A48 are metal - not plastic. :roll:

January 28, 2013 at 1:39 PM Flag Quote & Reply

Sir Alan
Posts: 457

Here's an example of a damaged day/date driving wheel:

(the damage is at about 1:30pm)

November 25, 2013 at 4:15 PM Flag Quote & Reply

Site Owner
Posts: 12808

This thread got a little plug on TZ-UK yesterday:

So I guess I should add this as a further cautionary footnote for all 7A38 owners, existing and prospective ....

There is one plastic gear in a 7A38 - the Day / Date driving wheel (Seiko part # 867.725). It is the weakest link.

Unfortunately the part is now officially 'discontinued' by Seiko and no longer available from Cousins UK:(

Another very good reason to exercise care when setting the Day / Date on a 7A38. ;)

November 11, 2014 at 5:30 PM Flag Quote & Reply

You must login to post.