Dual motor quartz radio clock – how does it work?

[Adrian R2Participant @adrianr2]

My workshop clock packed up, it is of the radio (MSF) synchronised quartz analogue type, symptoms are that the second hand ticks but then gets stuck at one point on the dial and doesn’t move on. A new battery made no difference so I took it apart and discovered it contains two lavet type motors coupled to a common gear train. Both still spin and no obvious FOD or damage to gears.

Just out of curiosity before I succumb to replacement (its not an expensive one), can anyone explain how this works, more specifically why the need for a second motor and how they work together to keep and synchronise time?

[John HaineParticipant @johnhaine32865]

IIRC when you switch these on you see the seconds and minute/hour hands move independently during the setting process.  If they didn’t it would take a long time to get the minute/hour hands right if you could only move the seconds hand.  Thus two motors are needed, and there isn’t a mechanical connection between the seconds hand and the train, it’s done by the chip.

[Adrian R2Participant @adrianr2]

Ah, that makes sense, I hadn’t considered that second hand and hours/minutes could be two independent drivetrains.

Thanks John, I will ponder that and see if I can work out the failure mode.

 

[Neil AParticipant @neila]

I have a radio controlled alarm clock sitting on the desk beside me at the moment which has exactly the same problem every so often. The second hand sticks in random positions. On my clock I find that giving it a good shake eventually frees it up and it will then run for a few months before sticking again. I’m just waiting to see if the shaking I have just given it is going to work and the answer is, not this time, it may be too worn now.

It had not occurred to me that the second hand was driven by a separate motor, obvious now that you point it out for the reason that you give.

The motor for second hand gets much more wear than the other motor and so will be the first to show any problems. My clock is more than thirty years old, just think how many times that second hand has stepped!

If I can’t get the second hand to step I shall do without it until the clock fails completely, it still keeps time, just no second hand.

Neil

[John HaineParticipant @johnhaine32865]

In these clocks the s/h motor actually has it easier than in a conventional quartz as it only has to drive one hand.  Not all that much easier though since there’s a 30:1 reduction between motor and hand.

[old martParticipant @oldmart]

My Casio digital/analogue watch which is solar powered for it’s rechargable battery has three motors powering the hands which are independent, not geared. There is a function in the menu to individually align the hands. The movement is Japanese and the case and strap is Chinese. There is a posher model which gets radio time signals.

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