Seiko 7A38 - by the numbers

Subtitle

Forums

Post Reply
Forum Home > Parts Info, Tech Tips and Tinkering > 7A28-702A chronograph setting problem

MTX371
Member
Posts: 46

Guys,


I need your help...

Have the above mentioned beauty.

Problem is that there is anything wrong, but I don´t know how to solve the problem.

If I pull the crown to the first position to set the totalisators and I push the start button - the stopwatch starts!

What´s that?!


Cheers!

Tim

January 11, 2014 at 2:00 PM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 14136

Probably a bent changeover switch lever / setting lever, Tim.


See: http://www.seiko7a38.com/apps/forums/topics/show/9397929-problems-with-stem-and-resetting-chrono-hands

January 11, 2014 at 2:15 PM Flag Quote & Reply

MTX371
Member
Posts: 46

It worked!!! :D

A thousands thanks!

January 11, 2014 at 4:44 PM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 14136

No worries, Tim - it happens to the best of us eventually. :D


See: http://www.seiko7a38.com/apps/forums/topics/show/9414421-a-very-long-term-restoration-project-7a38-7000-with-patina ....

.... and scroll a long way down the thread. 




 I would have seen that the setting lever's switch contact (to the PCB) was well below the surface of the '710' insulator spacer. 


January 11, 2014 at 5:41 PM Flag Quote & Reply

MTX371
Member
Posts: 46

Hi all,

again a problem:
stopwatch doesn´t work at all and also the manual setting of the totalisators doesn´t work.

I already had a look at the above mentioned setting lever, but this seemed to be ok and on the right position...
The sweep second hand is shaking when trying to set it manually... The other two do nothing.

Any ideas?

Cheers!
Tim

February 19, 2014 at 6:20 AM Flag Quote & Reply

GeorgeClarkson
Member
Posts: 508

Have a look here:

 

http://www.seiko7a38.com/apps/forums/topics/show/7280029-the-all-too-common-displaced-finger-tension-spring-chrono-sweep-hand-problem

 

This could be the issue, it happened to one of my 7A48's, and after correcting the position of the finger tension spring (which was misplaced), the problem was solved.

--

My personal Blog: www.onlyvintagewatches.com/blog

February 19, 2014 at 9:27 AM Flag Quote & Reply

MTX371
Member
Posts: 46

Nope, that´s all right...

Das war es nicht... Grüße nach Berlin... :)

February 19, 2014 at 12:56 PM Flag Quote & Reply

MTX371
Member
Posts: 46

Is it possible that the switch lever / setting lever is too high as well!?
We assume this being to low...

Can I check the functions directly after adjustment or do I have to reassemble the movement?

February 20, 2014 at 1:52 AM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 14136

Depends what you mean by 'reassemble the movement', Tim. :/

You certainly don't need to reassemble the movement into the watch case to test it. I've tested many movements on the bench ....

out of their watch cases - by pressing the exposed cams of their switch levers with a screwdriver blade.

But you certainly need to have the movement itself fully assembled, with all 7 screws on the back-plate tightened down properly ....

AND a crown and stem fitted and pushed fully home (thereby operating the setting lever), before you attempt any kind of testing.

February 20, 2014 at 11:24 AM Flag Quote & Reply

MTX371
Member
Posts: 46

Thanks, that I wanted to know - movement has to be fully assembled... It´s clear, that is needn´t be in the case... :P

Any more ideas for my problem?

February 20, 2014 at 1:46 PM Flag Quote & Reply

Rob Benham
Member
Posts: 281

One of the Test Points at the lower left, just right of the three on the edge, will show the voltage ON/OFF as the crown is moved.  I'm back working on a 7A38 tonight, I'll remind myself of the exact point. 

Taking readings off these TPs has to be done with great care.  Just touching the back plate at the same time might hit the chip with a load it can't tolerate.  Best only done if you have experience with mini electricals.
.

That chattering of the sweep-second hand . . . does it pulse at one-second intervals?  i.e. as though jammed and trying to go.


February 20, 2014 at 10:45 PM Flag Quote & Reply

donwatch
Member
Posts: 568

I hate to say this    -BUT I had much sucess with taking the mvt. out of case and lightly drip   Ronsonol Lighter Fuel on mvtl--then blow dry with  canned air held at distance - it leaves no residue--won't hurt dial won't lift paint etc. I have had troubled 7A's start right up with all functions working after this treatment----I don't recmond this--- just say it works for me :roll:

February 20, 2014 at 11:59 PM Flag Quote & Reply

Rob Benham
Member
Posts: 281

It's quite possible, that would have got my 7A38-728A (with no time function) going.  Paul suggested heating it over several hours/days, but I suspect I just wanted to take the main bridge off. :roll:  It showed signs of 'pulsing' while stalled - hence my question to MTX.   However, I'll probably give the petrol method a miss.  8)

.

I confess I didn't check the voltages tonight - I became engrossed in a cosmetic issue, on which I'll post.  However, MTX, if you do need to progess that line of diagnostics, I'll be pleased to relay what little I've learned in the last few weeks.  (99% of which is thanks to this forum.)

February 21, 2014 at 2:01 AM Flag Quote & Reply

donwatch
Member
Posts: 568

Remember the Quartz movement , unlike a spring driven movement has no inertia and will stall with the slightest bit of dust or tarnish. A conventional spring driven movement will grind right through any object causing drag, Quartz with its stop and go can hang up. 

February 21, 2014 at 2:36 AM Flag Quote & Reply

Rob Benham
Member
Posts: 281

I like the concept of inertia - or the lack of it.  The SGP 7000 you're helping me with had a blob of hard blue/green stuff which totally stalled the acc-minutes.  I have no idea what that could have been, or how it got there but there was a lot of chattering on its sub-dial.

February 21, 2014 at 2:43 AM Flag Quote & Reply

MTX371
Member
Posts: 46

I tried out now your ideas...

The movement is completely working now (stopwatch, manual reset, self test), if it is out of the case

BUT... 

If I put the movement into the case... Stopwatch is running ok. But after stopping I can´t reset it with 4 o´ clock button... Manual reset possible with 2 o´clock and 10 o´clock totalisators, but not 4 o´clock?!?! No self test possible...

Very strange?!!

February 27, 2014 at 3:34 PM Flag Quote & Reply

Rob Benham
Member
Posts: 281

Are you sure the pusher is able to go full travel?  The dirt that gets in the dome of the button becomes as hard as plastic.  Do you get a positive click - the same as the 10 o'clock one for example. 

February 27, 2014 at 3:49 PM Flag Quote & Reply

MTX371
Member
Posts: 46

The pusher should be ok. Feels and looks like the other two... Is it possible that it is too short?!?!

February 27, 2014 at 3:51 PM Flag Quote & Reply

MTX371
Member
Posts: 46

The three have all the same length - of course... :/ Not sticky, nothing... :roll:

February 27, 2014 at 3:59 PM Flag Quote & Reply

Rob Benham
Member
Posts: 281

Oh, MTX, did you pick up on Paul's ("Seiko7A38") link about just how high the changeover switch lever has to be?  

In the picture is show the hight relative to a STEP in the timing shaft.   Very useful piece of information.

.

I'd not registered that before and it's quite important, since being too high can make marks in the circuit's gold printed contacts.  I've noticed they do that anyway, leaving minute traces of gold between the two possible points of contact, so if the lever was too high, I think that will make matters worse. .


February 27, 2014 at 4:05 PM Flag Quote & Reply

You must login to post.