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Discussion Starter #1
I recently replaced the movement in my SKX173 with a 7S26A movement (originally had the B). It was humming right along, fluctuating between +3 and +10 sec/day for the better part of a month. I was wearing it last Saturday and noticed it was suddenly 5 min ahead!

Using the Twixt app on my phone determined it to be running +7.6 min/day. Over the course of the week it has settled down to +2.1 min/day, but that's still far faster than expected. Popped the back and the regulator hasn't moved at all.

It normally sits on a winder overnight, hasn't been dropped or had any hard bumps; the only thing unusual about Saturday is that I was out walking around more than normal (that'll teach me to take advantage of the first decent weather we've had!). I had issues like this with the original 7S26B (although, it never ran right), which is why I swapped it for the "A." I appreciate any thoughts - I'm very green when it comes to automatics.
 

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Im no expert, but i have done a little research into the 7s26 movement.
AFAIK the "B" movement has problems with the hair spring jumping over the pin on the regulator arm at the slightest knock causing it to bind, and allowing the movement to run fast, i believe this was sorted out on the "C" movements.
I know that the A & B balance assemblies will interchange, perhaps your "A" movement has a "B" balance assy fitted
 

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could it have become magnetized at all? if its not the above (which I understand the cure is a swift tap in the palm of the hand on the 9o'clock side if you cant open it!)
 

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Did you have the 7s26A serviced before using it? This movement is between 10 and 20 years old.
If it hasn't been serviced, it definitely needs to be.

Don't put your watches on winders, it's not good for them :(
 

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Why's that ? I havent got a winder but just interested.
Wear.
Watches on winders are captive to the fixed positions they are strapped into so wear will happen the same places over and over. And the movement is rhytmic which can only lead to wear in the same spot.

On the wrist, watches experience all positions and change continuously while being worn. This will spread out any wear that happens. Movement of the wrist also exerts varying forces on the watch and the winding system. Sometimes light and sometimes strenuous but always differing.

Seiko even warns against watch winders on some models like the Spring Drive. I would imagine they have made test with winders in order to be making these recommendations.
 

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Discussion Starter #7
could it have become magnetized at all? if its not the above (which I understand the cure is a swift tap in the palm of the hand on the 9o'clock side if you cant open it!)
Magnetization! You know - I'd tried demagnetizing it, but had done so hastily and had left the caseback on. Your post reminded me of this possibility, so I popped off the caseback and made a couple of passes over my (very cheap) Chinese demagnetizer and viola! Back into the range of +8 sec/day! I'm absolutely stumped as to how it could have gotten magnetized, but at least the problem is soved.
 

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Discussion Starter #8
Thanks also to the others who commented. The movement was sold by a trusted member of SCWF and was recently serviced by him prior to selling. Your comments about the winder have now caused me to wonder if that could be the source of the magnetization....
 

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Wear.
Watches on winders are captive to the fixed positions they are strapped into so wear will happen the same places over and over. And the movement is rhytmic which can only lead to wear in the same spot.

On the wrist, watches experience all positions and change continuously while being worn. This will spread out any wear that happens. Movement of the wrist also exerts varying forces on the watch and the winding system. Sometimes light and sometimes strenuous but always differing.

Seiko even warns against watch winders on some models like the Spring Drive. I would imagine they have made test with winders in order to be making these recommendations.
Thanks, that does sound logical.
 
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