In my frequent prowls through secondhand shops, I stumbled on this positively gorgeous piece of pre-digital electronics — A Sony Digimatic Clock Radio
As I found it, it wasn’t working properly. The clock would run slow, and get stuck for hours at a certain time, before finally flipping around to the next minute. Something was wrong, so I plopped it on my bench and laid it bare to see if I could fix it…
Electronics from this era tend to be very modular, and this clock was no exception. The clock itself and the radio are two completely separate units, and can operate independently of each other. The only connection between the clock and the radio is the sensor that lets the radio know when the alarm time is reached, so it can flick on the radio or start to buzz.
Electric clocks from this era kept time in an ingenious way, completely different from what we’re used to today. Instead of using electronics to count the passing of time, the heart of these clocks is a synchronous AC motor, which uses the mains frequency of 60Hz (Here in North America, anyway) as a pacemaker to maintain a very precise rotational speed. These motors are very low power, and low torque, so any resistance at all can get them to bog down and cease to spin.
Old, dried up lubricant in the gearbox turned out to be the culprit in this case, and after a flush and a re-lube, everything was spinning fine. I was able to reassemble the clock, and get things working as close to new as I could manage.
Once I solved that problem, I had a look at the radio board. Although everything appeared to be working properly, there was a noticeable 60Hz hum from the speaker when the radio was on, as well as some static when adjusting the volume. As old as it is, the electrolytics in it were all way past their “best before” date, so I ran through and replaced them “while I was in there.” I also flushed out the switches and pots with CRC flushing cleaner to get rid of nasty noises when pressing buttons.
I did run into a bit of a jam with one of the electrolytics I needed to replace. The original was an axial cap, and the one I was replacing it with was radial, so I had to extend the positive lead with a bit of spare solid core wire to get it to sit where the old one was. I didn’t get any photos of the finished product, but here’s the old one — Took this photo to make sure I’d get the polarity right when I reinstalled it!
Everything turned out very well in the end though. The radio no longer has any hum, and the clock has been keeping excellent time on my bedside table.