For as long as I can remember, I've had a Smiths "Tuning Fork" battery clock on the wall. It was in my teenage bedroom, my first house, and still in our kitchen. For quite a while I didn't know what it was, other than a "battery clock", but some years back I'd discovered what tuning fork mechanisms were.
Recently, the clock stopped working. Wasn't a dead battery. So, I began investigations to find out what can go wrong with this type of clock. The mechanism looked fine, clean, no sign of damage. Therefore, look at the electrical circuit. That's really simple; transistor, capacitor, resistor and an electromagnet. Not much to go wrong, and my first thoughts were "capacitor" (electrolytic capacitors decay with age).
A bit of internet searching confirmed this thesis.
This page gave a value for the capacitor (0.47uF)
https://www.electronics-lab.com/forums/threads/tuning-fork-clock-jeco-co-japan-smith-clock.109282/
And this site gave a few photos of mechanisms
https://clockdoc.org/default.aspx?aid=12510
So, I ordered some 0.47uF / 65v capacitors (way over the voltage needed, but its a stock size at electronics suppliers, cost £0.04 each ! ).
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| red arrow = time adjuster, needs slotted screwdriver blue arrows = two fixing screws for plastic case yellow arrow = capacitor (this is the replacement) And, yes, I'm using an AA rather than C cell, because it fits, and I have lots of AAs around. |
Gaining access to the circuit required making a slotted screwdriver blade to undo the retaining nut on the time-adjuster. The screwdriver was made from a hex-driver piece, and a bit of gentle grinding with a mini-drill and grinding disc until I got the thickness of blade required. Having made the screwdriver blade, hold the outside of the time adjuster plastic in pliers whilst undoing the nut with a screwdriver. Then remove the time adjuster by gently pulling out.
Two screws and remove the plastic outer body, and gain access to the circuit board. Original solder on the board was "generous with the solder", so some melting and removing of excess was done, before un-soldering the capacitor (make a note of the negative marked leg!), then fit the new capacitor (right way round!) and solder in place.
Reassembly was just putting the case back in place, refit the two screws, then replace the time adjuster and its slotted nut. And then refit the battery and give the adjuster a "ping" to get the mechanism to turn over again.
