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Clock Speeds Up

August 11, 2012

I’ve had the same clock radio in my bedroom for over 20 years.  Digital clocks like this one use the 60 Hz power line for their time base.  They keep perfect time.  Mine always kept perfect time too, but suddenly it started to gain time, about 30 minutes a day.  It was waking me up early.  At first, I found this behavior difficult to believe, but every time I reset the clock, it sped up again.

The first thing I did was to look for similar incidents on the web.  Sure enough, it had happened to many other people.  They speculated that it was caused by noise on the power line, or that the noise filter in the clock had failed.  The only resolution I could find was to replace the clock radio.  That’s what I did too.  A new one cost me only $15.00.  The clock was better.  It had larger digits and did automatic daylight saving time changes.  It that works, it will be worth the cost to me.  My new clock radio did keep perfect time when I plugged it into the same electrical outlet as the old one.  The old one must have developed a fault.

Still, I wanted to investigate my old clock radio.  Perhaps I could replace a bad component in its noise filter.  The first thing I did was to plug it in on my workbench downstairs and leave it overnight.  It kept perfect time!  I didn’t expect that.  I took it back to the bedroom and plugged it in beside the new one.  Once again, it gained time.  The clock radio couldn’t be at fault after all.

The problem must have been noise on that power circuit.  It covers plugs and lights in both bedrooms.  Sure enough, the clock gained time when I plugged it in anyplace in those two bedrooms, but not when I plugged it in the living room.  All of the junction boxes for the suspect power circuit were in the basement.  I inspected those, finding no problems.  Maybe it was a faulty circuit breaker?  I switched that off and on, but it made no difference.  What else was on that circuit?  It couldn’t be the lights; the clock still gained time when they were switched off.  That only left a few appliances.  There was a TV and DVD player, a Sun Ray terminal and monitor, and a telephone answering machine.

I did notice something wrong with the Sun Ray terminal after I had flipped the breaker.  It’s simply a small computer that boots from EEPROM.  Normally it displays something on the monitor after it’s powered on.  This time the monitor was blank.  The lights were on but it wasn’t booting.  So I unplugged both the monitor and Sun Ray terminal.  This time, when I plugged in my old clock radio in the bedroom, it kept perfect time.  Success!  The Sun Ray terminal was misbehaving.

Finally, I replaced the Sun Ray terminal with a spare one.  It worked.  The clock still kept perfect time.  The old one must have had a faulty power supply.  I opened it up to inspect the power supply, I couldn’t see anything obviously bad.  I’ll set it aside for now, and use the spare one instead.  Where would I have been without a spare?  Now I have a spare clock radio too.

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