" bravely wrote to "All" (27 Oct 05 09:34:24)
--- on the heady topic of " Why aren't computer clocks as accurate as cheap
quartz watches?"

do From:
do Xref: core-easynews sci.electronics.basics:145659
do sci.electronics.repair:346469 alt.comp.hardware.pc-homebuilt:351295



do w_tom wrote:

Watches have an internal capacitor to adjust for each
crystal. I have never seen that capacitor on motherboards
since (I believe it was) the IBM AT. Furthermore, the PC
clock operates at two significantly different voltages that
will change crystal frequency. Battery voltage and voltage
when PC is powered will cause additional fluctuation. Which
voltage should they adjust the capacitor to? Just easier to
not install and adjust the capacitor.

do I have an ancient Seiko quartz with a trimmer inside, and by adjusting
do it I was able to make it accurate to 30 seconds a year. But few cheap
do watches have them, including none of those I tried in this test.


I bought a cheap $5 lcd watch years ago and noticed the circuit had
the solder pads for a trimmer cap. After adding the timmer and
adjusting, it was the most accurate timepiece in the house. When I
came across another identical watch many years later I did the same
thing to it too.

The adjustment was trial and error using CHU. Starting at the
midpoint, I kept cutting the error in half either side then set it
inbetween. Both keep great time, I never notice a difference even
longterm, perhaps a second per month if that.

How did you adjust yours, with a pickup coil and frequency counter?
I suppose that would be the logical way to do it but then again a
counter could be off a tiny bit too. The NIST over the internet seems
nice too but what are the sources of error with this?

A*s*i*m*o*v

.... I worked hard to attach the electrodes to it.