Jeff Liebermann wrote in
:

On Sat, 19 May 2012 08:51:38 -0400, "Bill Proms"
wrote:

I have 3 Intelli-Time LED alarm clocks around the house, just like the
one he

http://www.acurite.com/clock/alarm-c...ital-alarm-clo
ck-13027a2.html

I initially bought these due to them keeping time when the power goes
off and auto resetting for DST. There is a problem, however. Each of
the clocks becomes inaccurate over time. If I set them all manually
to the same time, within a few months, each one will be off by 3-5
minutes.

So I ask, what is the problem and is there any way to repair it?

Several problems and combination of problems.
1. Noise on the power lines triggering added pulses. This will make
the clock run fast.
2. Internal free running oscillator is off frequency.
3. Crappy design.

I once modified a vacuum fluorescent alarm clock to keep accurate
time. I opened the device, figured out what chip was used, looked at
the data sheet, and replaced the crappy RC oscillator with a 32KHz
clock crystal. When the AC power disappears, the display goes blank
and the internal 9v battery runs the clock. The problem is that the
battery drain was so high that it would kill the 9V battery in about 6
hrs. There was also no charging circuit. So, I replaced the 9V
battery with 4ea AA NiCd batteries (the clock chip would still run on
about 6VDC), and added a crude trickle charger.

was that a 32KHz crystal,or a 32KHz ceramic resonator?
I suspect it's the latter.that would explain the poor freq.stability.
You can trim up an XTAL oscillator.

--
Jim Yanik
jyanik
at
localnet
dot com