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Old 3rd Feb 2023, 2:56 pm   #1
Herald1360
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Default Battery quartz clock problem/questions

Not my usual area of interest but a clock with some sentimental value to a friend. It's a presentable "fake" oscillating balls under a clear plastic dome mantel clock with separate "pendulum" drive and clock motor pulse generator circuits fed from a common AA cell.


The oscillating balls bit works nicely as does the pulse generator (MB512 4MHz crystal controlled clock driver chip) but the clock motor now only responds to the pulses by stepping a few steps then just twitching. Holding it at strange angles may persuade it to run continuously (reminiscent of tired old tin alarm clocks!) so I suspect it's some sort of mechanical wear issue beyond my pay grade.


I was hoping to just drop in a standard cheap quartz movement but the case is too small for the widely offered 56mm square central hand drive units being only 59mm inside diameter. It's clearly not impossible to make a smaller, possibly non internal battery movement so I wonder if anyone here has any possible supplier knowledge?


The picture shows the existing rather nice looking motor unit in the clock head.


?
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Old 3rd Feb 2023, 3:14 pm   #2
paulsherwin
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Default Re: Battery quartz clock problem/questions

They sometimes behave like this when the voltage is low, either because of a tired battery (presumably you've checked that) or dodgy battery contacts or connections. Worth investigating before giving up.

Charity shops often have a range of quartz clocks with suitable movements for a couple of quid.
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Old 3rd Feb 2023, 3:27 pm   #3
Herald1360
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Default Re: Battery quartz clock problem/questions

I've been round those loops, Paul, no joy!

I am toying with the idea of boosting the drive voltage output from the clock chip though, nothing to lose and unlikely to damage anything except the clock battery life .
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Old 3rd Feb 2023, 4:29 pm   #4
TonyDuell
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Default Re: Battery quartz clock problem/questions

Most of these Quartz movements have asymmetrical stator pole pieces and a magnetised rotor. The operating sequence is something like :

1) Current pulse through the coil in one direction causes the magnetic poles of the rotor to line up with the stator

2) No current through the coil. The rotor moves a little in the same direction to get into equilibrium again

3) Current pulse through the coil in the opposite direction causes the rotor to move a bit more in the same direction.

4) No current, moves a bit more in the same direction to get to the equilibrium state

Repeat...

Note that the asymmetry of the stator determines the direction of rotation. You can take many of the cheap movements apart, turn the stator metal pole piece thing over (you often have to shave off a plastic peg which is there so it can't be misassembled at the factory), put it together and have a 'mathematician's clock' which turns anticlockwise.

But if there is too much friction in the pivots and gear train it won't do the movements with no current. The result is a twtiching clock. If that's the fault then increasing the coil current won't help really.

It's worth taking the movement apart and cleaning the pivots and teeth. Do not lubricate.
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Old 4th Feb 2023, 10:47 am   #5
Herald1360
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Default Re: Battery quartz clock problem/questions

That's very helpful, thanks. Sounds like a good reason to see what goes "sprooiiiinngggg!" when I start undoing screws!
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Old 4th Feb 2023, 11:05 am   #6
Robsradio
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Default Re: Battery quartz clock problem/questions

Itís probably just dried out or sticky oil, clean the wheels, pivots and plate holes.
Light oil will only be required if there are any metal pivots running in metal plate holes.
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Old 4th Feb 2023, 4:11 pm   #7
nicam49
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Default Re: Battery quartz clock problem/questions

There is a bipolar electrolytic cap in that circuit (usually)... maybe worth testing ?
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