Seiko 7A38-7000 Trimmer Adjustment

Seiko 7A38-7000 Trimmer Adjustment

Joined: September 6th, 2007, 4:05 am

September 16th, 2007, 9:10 am #1

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.

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Joined: September 18th, 2002, 11:12 pm

September 16th, 2007, 10:28 am #2

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.

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Joined: April 8th, 2007, 5:39 pm

September 16th, 2007, 10:30 am #3

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.

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
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Joined: September 6th, 2007, 4:05 am

September 16th, 2007, 11:06 am #4

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.

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.

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Joined: September 6th, 2007, 4:05 am

September 16th, 2007, 11:22 am #5

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
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.
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Joined: April 8th, 2007, 5:39 pm

September 16th, 2007, 12:08 pm #6

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

Best Regards,

MikeNovember
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Joined: October 4th, 2002, 3:48 pm

September 16th, 2007, 9:38 pm #7

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.

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.

^_^
Last edited by rothe957 on September 16th, 2007, 9:50 pm, edited 1 time in total.
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Joined: September 6th, 2007, 4:05 am

September 16th, 2007, 10:12 pm #8

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.

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.
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Joined: September 6th, 2007, 4:05 am

September 16th, 2007, 10:41 pm #9

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.

^_^
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.
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Joined: September 18th, 2002, 11:12 pm

September 16th, 2007, 10:43 pm #10

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.
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.
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