What degrades in an old digital clock that makes it start to run fast?

I have a digital clock that I’ve had for about 30 years. Within the past few years, the time has started going fast by about a minute every day or so. That is, if I set the correct time today, in about a month it will be about 30 minutes fast (e.g. say 7:30 instead of 7:00).

I’m not surprised that a clock so old is starting to fail, but what I’m wondering is what specific component inside the clock is failing that makes it run fast.

electrolytic capacitor(s) drying out?

I second the cap failing idea.

(get it? second? anyone? I’ll go away now)

A failing cap was my thought too.

I doubt the timing circuit relies on any electrolytic caps, and thirty years ago there would be a reliable voltage regulator in the power supply. If there are any cooling vents in the clock I would suspect dust is built up and shorting the circuit a little or changing the capacitance.

The timing circuit is probably based on a quartz crystal. That circuit might have some capacitors in it though, and that might be throwing the resonance of the circuit off if the caps have dried out and gone bad.

Bad power supply caps might be causing a lot of ripple in the supply voltage, and the counting circuit could be miscounting some of the ripples as clock pulses.

It’s also possible that it uses the 60 Hz AC line as its timebase. It used to be that they adjusted the AC line frequency to be almost exactly 60 Hz in the long term, so that old fashioned clocks using synchronous motors would keep time properly. In the short term, the clocks might be a little off, but they would adjust the generator speeds as necessary periodically so that the long term error was very low. In general, heavy loads would bog down the frequency during the day, and they’d speed things up at night.

Synchronous motor clocks have mostly been replaced by digital clocks that have their own built-in timebase, and a lot of folks began to think that they were wasting a lot of effort (and money) keeping the AC line frequency so accurate in the long term. But no one really knew for certain exactly how many folks really did still depend on the line frequency’s accuracy. So they decided to run an experiment. They would let the frequency drift as it usually does, but they wouldn’t try to hard to correct it in the long term. Then they would see who complained about it.

The experiment was supposed to start in 2011 and run for at least a year. I never heard about it ending, though, and I’m not sure that they actually keep the line frequency accurate any more. It may be possible that this is what is throwing your clock off.

Do you have a source for this experiment? I’d like to read more about it.

Here you go.


That’s hard because you’d have to be a little bit of a specialist to have any idea what the problem was.

Very cool. Thankee, sir!

What would Einstein say?

Time is Speeding Up, Really!

ETA: If you have trouble opening that link, I found the same article here too.

The regulator also needs the filter at the end to smooth off ripple, and stop impulse noise.

Just like your TV picture might break up when the refrigerator or laundry machine operates its relays, the clock might be getting disturbed by noise on the mains power… Impulse noise has a way of jumping the transformer and transistor…

So … we didn’t do the test to see if the clock has degraded (bad caps and inductors in the regulator section failing to act as noise filters… ), Or its the white goods that have got worse…