Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

 
 
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w_tom
 
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Default Why aren't computer clocks as accurate as cheap quartz watches?

There are two ways to do as suggested. The first is to make
'Benjamins' part of the technical facts during design. The
second is to do the design, then let bean counters change the
design per what they 'feel' is not worth the bucks. The
latter is too often how GM cars are designed. Which is why a
GM car needs two extra pistons to get the same horsepower as
the competition. Which is why GM cars even in the 1990s
required annual wheel alignment. Which is why GM cars would
have what appeared to be computer failures when failure was
really due to cheap connectors. Classic examples of failures
when the design is modified after the design.

Two examples: how 'Benjamin' decisions become part of a
successful design verses how 'Benjamin' decisions after
application of technical facts makes bankruptcy.

Meanwhile, the technical reason for high verses low accuracy
timers was provided. Computer motherboards don't have the
trimming capacitor and the oscillator is subject to wider
voltage variations. Why this technical decision was made was
not asked and would only be speculation.

mike wrote:
There is no technical explanation except that the technology that
is being used does not guarantee accurate clocks.

If you do the math, you'll uncover the fact that a wris****ch is
phenomenally accurate compared to a RTC crystal.

I haven't been responsible for a computer design since 1989. Back
in the day, the philosophy was, "design for the center of the
statistical distribution and fix it in software."
Fortunately, UINX was smart enough to do time correction.

I haven't been responsible for a frequency counter design group since
1975. Back in the day, the philosophy was, "use the cheapest timebase
that guaranteed the specified accuracy."

I've had motherboards where they saved a nickel by leaving off the two
caps on the Xtal. Adding the caps helped, but "net time" fixed it in
software.

Are we seeing a trend yet?
You can get any accuracy you're willing to pay for. Computer users have
voted with their wallets for "lousy". I don't remember ever seeing a
specification for real time clock accuracy on a motherboard.
So if the clock ticks, it's in spec. Statistically, you'll sometimes
get one that's unacceptable and some of those will get bitched about on
the internet. It's the same reason that sometimes your Ford won't run
right.

You're the Chinese engineer. Go tell the bean counter that you want to
add 20 cents worth of parts to adjust the clock frequency, add $4000
worth of capital equipment to each production station, a week of
additional production line time to setup and program the equipment,
30 seconds of operator time to each board test and decrease the overall
yield.

It really is all about the Benjamins.
...

 
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