<< Previous Topic | Next Topic >>Return to Index  

Seiko 7A38-7000 Trimmer Adjustment

September 16 2007 at 2:10 AM
No score for this post
Charles  (Login Chucky7)
from IP address 203.214.137.186

 
I hava a Seiko 7A38-7000 and have adjusted the watch down to an accuracy of about 1sec per month using the atomic clock as a reference.
I beleive each division on the scale is about 0.25sec per day.
The way to adjust it is to set it and leave it running 4days then check it again.
I will see how low i can set it.

Cheers
Charles.


 
Scoring disabled. You must be logged in to score posts.Respond to this message   
AuthorReply

Time2Fly
(Login H_Pham)
Approved Users
24.255.217.32

re: 7Axx Trimmer Adjustment

No score for this post
September 16 2007, 3:28 AM 

I have a pdf file for the 7A28 that says each step on the trimmer adjustment is 0.26 sec/day (about 8 secs/month). I've adjusted one of my 7A's to +5 secs/month. You already got yours down to 1 sec/month. Without sophisticated measuring equipment, it'd be tough to tweak it any better than that.


 
Scoring disabled. You must be logged in to score posts.Respond to this message   
Charles
(Login Chucky7)
203.214.137.186

Re 7A38 Trimmer Adjust

No score for this post
September 16 2007, 4:06 AM 

Good to hear from you.

As some one who has been in the electronics industry for more than 40 years,
I think using the atomic clock as a reference is the only way to check the accuracy of a watch.
Checking the crystal oscillator frequency does not take into account
the wear on the gears,stepper motors and other mechanical components of the watch.
Setting the watch using the atomic clock and letting it run for a month
and checking it with the same atomic clock 1 month later is the only way.

Cheers
Charles.


 
Scoring disabled. You must be logged in to score posts.Respond to this message   
Charles
(Login Chucky7)
203.214.137.186

Re Time2fly Trimmer Adjust

No score for this post
September 16 2007, 3:12 PM 

Hi Time2Fly

Your original setting of 30 secs per month was way off the specs of +or- 15secs per month Seiko claims for the 7Axx series.
I just checked my Trimmer adjustment and compared it to to your photo
of the second trimmer adjustment of +5sec per month, thats about where my original setting were set at.
Mine is set half way between the second and third divisions on the left for 1sec per month accuracy.
Of course there may be slight variations from one watch to another,but there is no harm in trying.
I will try to set it the lowest i can adjust it between normal and daylight saving time.
Lets see if i get down to the accuracy claimed for the Citizen Campanola watches or the Citizen MegaQuartz watches with a accuracy claim of +or-3secs per year.
And use the atomic clock as a reference.

Cheers
Charles.

 
Scoring disabled. You must be logged in to score posts.Respond to this message   

Time2Fly
(Login H_Pham)
Approved Users
24.255.217.32

A few thoughts...

No score for this post
September 16 2007, 3:43 PM 

1. Based on Michael Rothe's post below, I don't know if adjustments can be made in amount of less than 0.26 sec/day.

2. Assuming adjustments can be made in amounts of less than 0.26 sec/day and change in a linear fashion: one "tick" on the adjustment scale equals 0.26*365 = 94.9 secs/year, a person would have to have a real steady hand to adjust it down to 2-3 secs/year.

 
Scoring disabled. You must be logged in to score posts.Respond to this message   
Charles
(Login Chucky7)
203.214.137.186

Re Fine Trimmer Adjustment

No score for this post
September 16 2007, 6:02 PM 

Hi

I agree it would be difficult but not impossible.
At the moment i am using a pair of stright tweezers,but had the thought of
making a tool similar to an allen key with a 90 degree bend so you can see
the fine adjustment in a circular arc ,that way you should be able to see
adjustments down to a few degrees.
With this you should be able to make very fine adjustments at the trimmer axis.
Using 1sec per month accuracy as my reference point.
You would have to to make adjustments of only a few microns, as i said difficult but not impossible.

As Thomas Edison said "Genius is 99% Perspiration and 1% Inspiration"

Cheers
Charles.

 
Scoring disabled. You must be logged in to score posts.Respond to this message   
Charles
(Login Chucky7)
203.214.136.39

Re Time2Fly's Photos

No score for this post
September 17 2007, 1:46 PM 

Hi Time2Fly

Just had a closer look at your 3 photos of your 7A28 adjustments, I noticed on the original setting using the copper colored end of the trimmer on the right as a reference point it is actually set off the scale.
If you look carefully at all of the adjustments they are actually in between all of the markings. According to Michael Rothes posting this should have no effect on the adjustments as they are preset to increments 0.26 secs per day per division .
I have downloaded the Seiko pdf file and looked at the exploded view of rotary step switch and i am puzzled at the way this thing actally works.
Looking forward to your comments on this.

Cheers
Charles.


 
Scoring disabled. You must be logged in to score posts.Respond to this message   

Time2Fly
(Login H_Pham)
Approved Users
24.255.217.32

re: Adjustments...

No score for this post
September 17 2007, 7:20 PM 

Not having a background in electronics, I don't feel qualified to join the debate between you and Michael on whether or not adjustments can be made at less than one division on the scale.

However, based on the adjustments that I showed in my photos, it does look like one division equals 0.26 sec/day (7.9 sec/month). In the 1st photo, the watch was running +30 secs/month. In the 2nd photo, the knob was moved two divisions (2 x 7.9) and the watch was slowing down to +15 secs/month. In the 3rd photo, the knob was moved another division (7.9) and the watch slowed down to +5 secs/month (give or take a few seconds).

I don't think the "wings" on the knob has to line up with the division marks on the scale. The marks are just guidelines to show how much the knob was turned.

 
Scoring disabled. You must be logged in to score posts.Respond to this message   
Charles
(Login Chucky7)
203.214.128.91

Re Rotary Step Switch Adjuster

No score for this post
September 18 2007, 1:13 AM 

Hi Time2Fly

Have a look at Michaels Photos regarding the the rotary switch it is now
obvious that the adjusts are made in steps of 7.8secs per month or 0.26 secs per day.It is strange that your adjustment went from 15secs per month to 5secs per month a difference of 10secs, this should have been 7.8secs.
It would seem that this is not linear,as mine went +5 secs per month to 1sec per month.
This could be put down to minor differences in the quartz crystal.
If you adjust yours one more step you might get it down to +-1 sec.


Cheers
Charles.

 
Scoring disabled. You must be logged in to score posts.Respond to this message   

Time2Fly
(Login H_Pham)
Approved Users
24.255.217.32

re: Adjustment amounts..

No score for this post
September 18 2007, 3:45 AM 

> It is strange that your adjustment went from 15secs per month to 5secs per month a difference of 10secs, this should have been 7.8secs.

I only monitored it for a short duration. With a margin of sampling error of 1 second, it could've been from 14secs down to 6secs, which is a difference of 8secs, perfect fit.

I've sold that watch. The rest of my 7As collection (10 of them) are fairly accurate, don't really have time and motivation to mess with them.

 
Scoring disabled. You must be logged in to score posts.Respond to this message   
MikeNovember
(Login MikeNovember)
80.170.70.87

Re: Seiko 7A38-7000 Trimmer Adjustment

No score for this post
September 16 2007, 3:30 AM 

Hello,

Trimmer adjustment should be done only on "old" watches, in order to compensate quartz slow wear. It generally requires specific electronic equipment.

It should not be done on a new watch: you would never arrive to get the same accuracy.

You can have some very good surprises with Seiko accuracy performance, which is often well better than the catalog announced one. My "Pipin" is equipped with 5M65 caliber, given for +/- 15 s per month.

The drift, compared to an atomic clock reference, is -1.5 s in 4.5 months! that means less than -5 s per year! And I have noticed that almost all the drift occurred in the first month of use of the watch, it seems now to be stabilized!

Best Regards,

MikeNovember

 
Scoring disabled. You must be logged in to score posts.Respond to this message   
Charles
(Login Chucky7)
203.214.137.186

Re 7A38Trimmer Adjustment

No score for this post
September 16 2007, 4:22 AM 

Hi

My watch is 19yrs old so i think the crystal is stable enough to adjust.
Before adjustment it was about +5 seconds fast a month.
Seiko only claim an accuracy of +or- 15secs a month which i think is conservative just to be on the safe side of the specs.
I think they would only adjust the watch at the factory by setting the quartz
oscillator to a specific initial setting and not waiting a month using an
atomic clock.

Cheers
Charles.

 
Scoring disabled. You must be logged in to score posts.Respond to this message   
MikeNovember
(Login MikeNovember)
80.170.70.87

Re: Re 7A38Trimmer Adjustment

No score for this post
September 16 2007, 5:08 AM 

OK! After 19 years it is time to compensate the quartz slight degradation using the trimmer!

Best Regards,

MikeNovember

 
Scoring disabled. You must be logged in to score posts.Respond to this message   
Michael Rothe
(Login rothe957)
Approved Users
87.162.42.234

The 7A series has no real trimmer, it's a multi-stage switch

No score for this post
September 16 2007, 2:38 PM 

Some watches have a real trimmer capacitor which allows for fine adjustment, but has it's own aging and temp drift problems.
The 7A series is equipped with a multi-stage switch that allows adjustment in steps of 0.26s/day.
The 7A28 technical guide calls it a 'rotary step switch'.
Adjusting is done by changing the number of pulses to be counted for a time span of 10 second.
Normally, the watch counts 32768 pulses per second, or 327680 pulses in 10 seconds.
If you count one pulse more or less (i.e. making every 10th second a pulse longer or shorter,
for a total of 327681 or 327679 pulses), you adjust the timing by a fraction of 1/327680.
For a day with 24*60*60=86400 seconds, this fraction is about 0.26 seconds.
For a month (or 30 days) the adjustment 'step size' is 7.9s.
So you're very lucky to have a 7A that can be adjusted to 1s/month.

PS: There really is no trimmer capacitor. I've taken apart a dead 7A28 a few years ago (no pics taken, sorry).
The switch is just a piece of metal with two contact 'tongues' that connects different pairs of a circular
pattern of gold plated pads on the circuit board, depending on it's position.

^_^


    
This message has been edited by rothe957 from IP address 87.162.42.234 on Sep 16, 2007 2:50 PM


 
Scoring disabled. You must be logged in to score posts.Respond to this message   
Charles
(Login Chucky7)
203.214.137.186

Re Trimmer Adjust

No score for this post
September 16 2007, 3:41 PM 

Good to hear from you Michael.

I have been in the electronics industry for more than 40yrs.
These plates you turn vary the capacitance just like you do in a RF oscillator
on the old radio tuners.
I have tried many settings between the divisions and they do make a very
small difference in the settings.
Those are not just set at 0.26sec per divisions on the watch.
The trick is in turning the trimmer in minute movements to achieve the very small increments needed to set the watch.
I only used a pair of tweezers for the adjustments so i was lucky to get the setting to where i am at now of 1sec per month.
The only way you could better this would to have something like an allen key
with with a 90 degree bend so you can see the adjustments as the degrees of an arc,if you can see what i'm getting at.

Cheers
Charles.

 
Scoring disabled. You must be logged in to score posts.Respond to this message   
Michael Rothe
(Login rothe957)
Approved Users
87.162.66.8

It's really not a trimmer capacitor

No score for this post
September 17 2007, 1:11 AM 

I've seen enough trimmers in other watches, and the thing in the 7A is definitely not a trimmer.
The moving part of the switch is a single piece of metal that simply connects two pads on the circuit board.
I mean, even the Seiko technical guide states it's a step switch.
It also states that it should be set only at the marked positions,
and it states that adjustment works in steps of 0.26 seconds/day.
Just read it here: http://service.seiko.com.au/i/seiko/documents/technicalguides/7A28A.pdf
Even if your experience is otherwise, I don't think the writers of the Seiko technical guide got it wrong.
They built the thing - if they say it's a switch, then it's a switch.
There must be another explanation for the small adjustment steps you achieved.
Maybe Rob T. can supply a pic if he takes apart his junker movement.

Another hint in the manual is that one must use a quartz tester in the 10-second gate mode to get accurate readings.
Watches with a real trimmer capacitor adjustment don't require this averaging mode, because the quartz frequency is
adjusted directly, and every second is counted as 32768 pulses.
If you compare the movement specification table in the tech guide of the 7A28 with another movement that
really has a trimmer condenser (e.g. the Seiko 7546A), you can see the difference:
Entry 'Regulation system': 7A28: 'Rotary step switch', 7546: 'Trimmer condenser'
Also, the 7A28 spec has the entry for the quartz tester mode to be used, and the 7546 does not.

^_^


    
This message has been edited by rothe957 from IP address 87.162.66.8 on Sep 17, 2007 6:37 AM


 
Scoring disabled. You must be logged in to score posts.Respond to this message   
Rob
(Login 5seikos)
Approved Users
96.229.179.207

Then one cannot make an adjustment in between the marks

No score for this post
September 16 2007, 9:50 PM 

as there are no valid setting in between? I have seen variable caps on quartz movement, which I though these were. I have a junker movement, I think I'll have a look.

Regards,
Rob T

 
Scoring disabled. You must be logged in to score posts.Respond to this message   
Michael Rothe
(Login rothe957)
Approved Users
87.162.66.8

Exactly. That's what the Seiko technical guide says

No score for this post
September 17 2007, 1:22 AM 

Can you take pics when you take apart your junker movement?
I missed the chance back then.

^_^

 
Scoring disabled. You must be logged in to score posts.Respond to this message   
Charles
(Login Chucky7)
203.214.136.39

Re Cannot make adjustments between marks

No score for this post
September 17 2007, 1:53 PM 

Hi

If this is so have a close look at Re Time2Fly's Photo Response and his original photos in his in his original posting.
Dont you just love a good mystery!.

Cheers
Charles.

 
Scoring disabled. You must be logged in to score posts.Respond to this message   
Michael Rothe
(Login rothe957)
Approved Users
87.162.66.8

Found my old 7A28 junker mov't - pics! (Updated)

No score for this post
September 17 2007, 3:13 PM 

I found the old movement and realised that all the parts were still there.
So I took it apart again, and this time I made a few pics. Here goes:

'Before': Antimagnetic shield plate still in place, rotary switch visible in the lower left part:


Antimagnetic shield plate removed, circuit block visible:


Circuit block removed and flipped over, rotary switch hole and contact pads in the lower right part:


Movement without circuit block, circuit block spacer visible with rotary switch rotor (two-pronged thing in the lower left part):


Better view from the side:


The rotor sits on a metal part (pivot? axis? don't know the correct word):


...which is connected to the mainplate and thus to battery plus:


Detail view of rotary switch rotor and contact pad pattern:


You can even see where the switch rotor left its imprints.
I think setting the adjustment works by connecting none, one or two pads to battery plus through the rotor.

Here is an overlay picture of the adjustment markings and the contact pattern on the circuit block:


Lets name the upper two pads (connected to the same wire) 'A', the lower left pad 'B' and the lower right pad 'C'.
The marks on the antimagnetic shield plate indicate three steps in the plus direction and two steps in the minus direction.
Default position (pre-adjusted in the factory): no pads have contact to the rotor
Plus step one: pad A has contact to the rotor
Plus step two: pad A and pad B have contact to the rotor
Plus step three: pad B has contact to the rotor
Minus step one: pad A and pad C have contact to the rotor
Minus step two: pad C has contact to the rotor

With three digital bits (line A,B and C), one can represent 8 different states.
6 of 8 combinations are used here (all open, A, B, C, AB, AC). The two unused combinations are BC and ABC:
- ABC: all three pads connected to the rotor (impossible with a two-pronged rotor)
- BC: pad B and pad C connected to the rotor
this would be possible with a slightly smaller pad size (7 positions instead of 6 on the semicircle),
but it seems Seiko thought that an adjustment range of -16s/month to +24s/month was sufficient

You can read more about the 7A28 movement in the Seiko Technical Guide, available here:
http://service.seiko.com.au/i/seiko/documents/technicalguides/7A28A.pdf

^_^


    
This message has been edited by rothe957 from IP address 87.162.67.241 on Sep 18, 2007 5:40 AM


 
Scoring disabled. You must be logged in to score posts.Respond to this message   
 
< Previous Page 1 2 Next >
  << Previous Topic | Next Topic >>Return to Index  
 Copyright © 1999-2017 Network54. All rights reserved.   Terms of Use   Privacy Statement  
Watch Top 100's by Connectingwatches.com