[time-nuts] Adjusting accuracy of a Casio G-Shock watch

[Bill Hawkins]

Jim,

I have such a watch, purchased in Singapore in Oct 2009. It is
solar, but it has no radio connection. It is water-resistant
to 20 atmospheres (bar). I don't wear it, but I keep it by a
southern window.

The back cover appears to be held on by four screws. I've not
tried to open it. It's off by two hours and 91 seconds, over
a year. It's possible that I didn't make the final time zone
adjustment when I got back to Minnesota.

What was the problem with getting the back off?

Bill Hawkins
 

-----Original Message-----
From: Jim Palfreyman
Sent: Tuesday, December 14, 2010 10:17 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Adjusting accuracy of a Casio G-Shock watch

Fellow time-nuts.

Over in another part of the internet is a group of people who love their
Casio G-Shock watches. These digital watches have been around for decades
and are built very well.

The one I own is an "atomic" and solar model (i.e. no battery replacement).
However being in Tasmania, I cannot receive the low frequency time signals.
When I first received the watch it's accuracy was excellent. Under 10
seconds a year. I even posted on here about it. Since then though it has
drifted somewhat.

After a ton of internet searching on how to open the case and how to adjust
these watches (this is non trivial as the models are all very different and
no instructions existed for this model - the GW-810D) I have finally cracked
it.

Interestingly, the module has a pad that gives off a stepped square wave at
32768/48 Hz. So with well calibrated equipment (which we all have of course)
it is trivial to adjust the trimmer to put the watch back to decent
accuracy. Using the smallest adjustment of the trimmer that I could muster I
could get it down to about 0.5 in 10^6 or 1 second in around 20 days. Not as
good as when I got it - but I was probably just lucky.

Over in mygshock.com they struggle with this sort of timing stuff - whereas
my big deal was opening the case!

Just posting in this in case anyone here is interesting in adjusting their
G-Shock.

Jim
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