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Sunday, 22 November 2015

Clock repair

Some 30 years ago, I was getting a pain in my wrist when I was typing, and I thought "RSI". That's a horrifying thought for someone who's a programmer and a writer - I use a keyboard a lot. Then I noticed that I was taking off my wristwatch before typing, so I left it off, and my wrist pain felt better. I don't know if there's a connection; the human body is very self-repairing even if you do nothing. But I made a discovery at that time - I very rarely need to know the exact time. So I completely stopped wearing a wristwatch, and never have since then - there's no point.

I was commuting to work at that time, down to the City. To go home, I could go either to Baker Street or Marylebone station, and the choice of which depended on the exact time. I'd get onto the Bakerloo line, and according to the exact time, I'd get off at either Baker Street or Marylebone. So you can see that it was quite important, at that one moment in the day, to know the exact time.

So I went to Dixons, and bought the AQ11 digital clock, kept it on my brieface, and looked at it as the tube approached Baker Street, and made my decision.

Now roll forward 30 years to today. I still have the AQ11, it still works, and it still keeps very good time. A clock I bought on Ebay for a couple of pounds, gains about a minute per week, which is annoying because for it to be useful, I have to keep resetting the time. The AQ11 is dead on.

So it's a good clock, and I like it, but. I couldn't change the time, and I didn't know why. This isn't a big problem, except that when I change the battery. How do I set it to the correct time?

So I decided to dismantle and fix it. I always start from the assumption that I can fix anything, and that turns out to be true nearly all the time. I took out the two screws near the battery, and wiggled and twiddled it until it came apart. Then there's two black screws inside. Once those are unscrewed, the PCB comes out, and I could see the problem.

The way that the time is set, is three push buttons. When you press each of those, a pad touches bare wires on the PCB and that's a switch closing. But for that to happen, there must be something conductive on the bottom of the button, and that was gone. There was a small amount of green flakes there, and a couple of black bits (which I guess are conductive).

So how to fix this? I took out the three buttons, which means that I can now see the bare wires on the PCB, and if I touch that with a screwdriver or similar, that's equivalent to pressing one of the three buttons.

So the fix turned out to be, remove the three buttons used for setting the time, and poke with a screwdriver instead.

And now my beloved AQ11 works!

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