Seiko 7A38 - by the numbers

Member
Posts: 109

Hi,

after setting all hand s to zero position I have a problem with one of my 7A's.

When i reset to zero the subdial hands will not stand stil correctly .

Everytime they go a few steps forward.

Changing the Circuit has no positive effect.

What would be solution?

I need help to solve this problem.

January 28, 2013 at 4:10 AM

Site Owner
Posts: 14428

Hi, Andre. I'm not sure I understand your problem. What exactly do you mean by 'will not stand still correctly' ?

Are they twitching ? Do they go to zero and then advance a few steps by themselves ?

Which hands are affected ? Just the sweep second hand, or the two chrono' subdial hands as well ?

January 31, 2013 at 4:52 AM

Member
Posts: 109

Paul,

the 5/100 and minute subdial hands

they go to zero and then advance a few steps.

I changed the circuit with a known correct working one and the behavior is the same.

First time i have no idea,

the movement is from a "new " 7A collectionmember with unknown servicehistory.

January 31, 2013 at 5:00 AM

Site Owner
Posts: 14428

Sounds very odd.

I presume the switch actuator levers on the baseplate are clean, correctly postioned and moving freely with a nice clicky action and that none of the pushers are sticking ?

January 31, 2013 at 5:25 AM

Member
Posts: 109

Right Sir,

switch actuator levers on the baseplate are clean, correctly postioned and moving freely with a nice clicky action and none of the pushers are sticking.

Pushers were cleaned and lubed.

January 31, 2013 at 5:36 AM

Site Owner
Posts: 14428

O.K.. Next question - and I'm clutching at straws, here ....

When you try operating the chrono', are you sure the crown (stem) is pushed fully home - i.e. it's not at the 'first click' setting position ?

(There is a slight chance someone may have fitted a new stem and cut it too short).

January 31, 2013 at 6:00 AM

Member
Posts: 109

Stem is OK,

I can set all hands to zero in 'first click'setting.

And use the stopwatch corectly: main second counting, 5/100 second counting, minute counting until powersave.

After stopping and reset - the subdials wont stop at zero position

Same behavior in the hands test mode.

January 31, 2013 at 6:19 AM

Site Owner
Posts: 14428

When they overshoot, after you have reset them to Zero, do they always stop at exactly the same place ?

January 31, 2013 at 6:47 AM

Member
Posts: 109

They are always going a few steps forward not exactly the same place.

Seems that they make a full round trip and they cannot stop.

January 31, 2013 at 7:45 AM

Site Owner
Posts: 14428

O.K. Andre. If we've eliminated electronic and mechanical - how about magnetic ?

Would you feel brave enough to try removing the 1/10s and 30 minute counting bridges ? I'm not saying this could definitely be the cause, but possibly either the stepper rotors have lost their magnetism, or the stators have become magnetised. Before you consider that option, have you tried pushing those two hands around manually (with the point of a cocktail stick). Can you feel any resistance ?

January 31, 2013 at 9:18 AM

Member
Posts: 109

Have to try this next week.

I'll disassemble the movement bridges.

January 31, 2013 at 9:27 AM

Site Owner
Posts: 14428

Try the 'hand nudging' test first.

If you've done it before, then you'll know that you can feel a certain 'lumpiness' between the marks. That's not backlash in the gears.

It's you turning the rotor within its magnetic field. I've also noticed, particularly with recalcitrant sweep second hands on 7Axx's, that when you try nudging them around the dial, there is virtually zero resistance. Perhaps that's where the problem stems from.

January 31, 2013 at 9:48 AM

Member
Posts: 109

If I understand it right:

Test with toothpick need a resistance.

No resistance means magnetic problem and change e.g. stepper rotors.

January 31, 2013 at 10:25 AM

Site Owner
Posts: 14428

Possibly, Andre. But you really need to know what this 'resistance' feels like on a good movement to be able to compare it.

January 31, 2013 at 1:09 PM

Member
Posts: 109

Seems the problem have been solved.

After disassembling the movement and cleaning it with rodico there was too much oil for the subdials.

No magnetic problem - "only" too much oil

April 10, 2013 at 1:10 PM

Posts: 58

I have a similar problem. The 1/10 sub-dial is re-setting to 0 correctly, but the minute sub-dial does not reset at all and the seconds hand does not reset to 0, but a few minutes before 0 each time and you need to press pretty hard for it to do move. I have read the suggestion above " I presume the switch actuator levers on the baseplate are clean, correctly postioned and moving freely with a nice clicky action and that none of the pushers are sticking ?", but don't know where to start being a complete novice. I have checked that the end of the extended portion of the clip is over the purple jewel in the centre of the movement ....

July 27, 2013 at 9:29 AM

http://www.seiko7a38.com/apps/forums/topics/show/7168318-essential-tools

Site Owner
Posts: 14428

"but don't know where to start being a complete novice."

Claus.

May I suggest that you dig out that email I sent you almost a year ago (18th August 2012), and start reading up the topics I linked.

In fact, I've found it myself. Here's a copy and paste of the relevant part of my email:

That's the idea of the forum - to help people interested in 7A38's become self-sufficient.

May I suggest you start reading topics in The Workshop section.

Some of those Simon (Sir Alan) has written are a good grounding.

http://www.seiko7a38.com/apps/forums/topics/show/7239393-taking-it-apart

http://www.seiko7a38.com/apps/forums/topics/show/7517616-inside-the-7a38

http://www.seiko7a38.com/apps/forums/topics/show/7614384-inside-the-7a48 (still relevant, they're very similar).

http://www.seiko7a38.com/apps/forums/topics/show/7709682-we-re-going-in-deep-inside-the-7axx

Regards, Paul.

July 27, 2013 at 5:02 PM

Posts: 58

Yes, you are right. There is even a picture of the 'PUSH' button to relase the crown stem...

July 27, 2013 at 7:33 PM

Rogus

Member
Posts: 8

I have a problem on a 7a38 whereby I can't reset the chrono hands using the proper method. I pull the crown out to the correct position and press the pushers but they continue to work as if the crown were in the "in" position i.e. they continue to operate the stopwatch instead of pumping the hands forward. Same thing happens in each of the crown positions, in, out and middle.

I've now moved the hands around to the correct positions using a cocktail stick and from here the test and stopwatch functions work fine. It is bugging me that something isn't right though - not being able to pump round the hands without taking the case apart..

Appreciate any thoughts

September 28, 2014 at 3:10 PM