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Dear_one
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14 May 2021, 2:07 pm

I have a bedside alarm clock with a red LED display that has started gaining about 11 minutes per day. How interesting is that to someone who knows how it might happen?



naturalplastic
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14 May 2021, 3:23 pm

Your clock is fine. Digital time pieces are infallible.

Its that YOU... are trapped in a real life version of the Bill Murray movie "Ground Hog Day". :lol:



Dear_one
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14 May 2021, 3:31 pm

naturalplastic wrote:
Your clock is fine. Digital time pieces are infallible.

Its that YOU... are trapped in a real life version of the Bill Murray movie "Ground Hog Day". :lol:


Heck, as your quiet house mate, I knew that, but from what little I know of digital clocks, something very odd has happened, because my watch disagrees substantially for the first time. I shall check an old synchronous motor clock, and try to fire up another LED one.



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15 May 2021, 9:19 am

I had a similar problem once. The issue turned out to be that it was made in China.


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16 May 2021, 8:14 am

If the clock has been good up until recently, it may be the backup battery(ies.) I had that happen once. Check the bottom or the back for the battery compartment and replace them, see if that helps.
The sort of clock I'm talking about is the plug-in sort, but with battery backup in case of power failure etc. If you have a strictly-battery one, it may still be the batteries. Things go all wonky when they get low but not dead yet.



naturalplastic
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16 May 2021, 11:51 am

Maybe it isnt "Ground Hog Day" that youve fallen into, but "Max Headroom" (the 80s show that was set "eleven minutes into the future". :lol:



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16 May 2021, 12:51 pm

Dear_one wrote:
I have a bedside alarm clock with a red LED display that has started gaining about 11 minutes per day. How interesting is that to someone who knows how it might happen?


I had this problem with quite an old bedside red LED alarm
clock.
When turning on the power it would keep time for about
5 minutes after which it would start to gain time.
The problem turned out to be an electrolytic smoothing
capacitor that's internal ESR had gone high, so it was no
longer filtering out the AC ripple.
I believe this ripple in the circuit was affecting the
crystal oscillator causing the time gain.
I replaced the capacitor and it's been working as normal
for about two years now.



Dear_one
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16 May 2021, 1:37 pm

Soliloquist wrote:
Dear_one wrote:
I have a bedside alarm clock with a red LED display that has started gaining about 11 minutes per day. How interesting is that to someone who knows how it might happen?


I had this problem with quite an old bedside red LED alarm
clock.
When turning on the power it would keep time for about
5 minutes after which it would start to gain time.
The problem turned out to be an electrolytic smoothing
capacitor that's internal ESR had gone high, so it was no
longer filtering out the AC ripple.
I believe this ripple in the circuit was affecting the
crystal oscillator causing the time gain.
I replaced the capacitor and it's been working as normal
for about two years now.


Thanks very much. I had only imagined some fault right in the chip, which could have been educational. I've replaced the battery, and if that does not help, I'll replace the clock with another used one.



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16 May 2021, 1:54 pm

Most clocks these days uses a quartz crystal to drive the mechanism / time accumulator. The quartz crystal is carved to be like a very tiny pendulum. If the voltage is constant the crystal build up charge like a capacitor and the force of static electric attraction builds up - the crystal can flex just enough that it will close the gap when the charge is high enough - then the circuit is complete and the charge drains and it starts all over again. The obvious thing is to keep the voltage constant so the cycle is also constant. Sometimes the power company will change the power being delivered - such as if they are seeing a drop on a specific line. Two things can happen: the frequency of the delivered power and/or the delivered voltage can change. If the clock doesn't have power conditioning then the voltage to the crystal can also go up - and you will get more ticks per second. Some cheap clocks don't use a quartz crystal at all and rely on the power company delivering a 60 cycle signal and use that as a clock instead of the crystal. Again if the power company changes the curve of the power delivered you can see it in the clock.

If either of these things are the problem then the root cause is a design problem in the clock and the solution is like the punch line to the old joke "what time is it when your clock strikes 13? time to get a new clock". You should probably try the previous poster's fixes first. If they don't work it may be easiest to just get a new clock (rather than conditioning the power with something like a UPS before the clock). Unless you really like to build electronics and you want to rebuild the clock.


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