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Inlaw's quartz clock issue


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I have my inlaw's quartz chiming clock to "repair" the issue is that the clock is losing time, I have heard that quartz clock movements have a life of 5 -10 yrs and as this clock is over 10 yrs old probably the obvious thing to do is replace the movement, but I can't source a chiming pendulum movement with a battery on the correct side for the cutout in the metal back of the clock case, the original movement is a Hermle 1237, I'm not keen to cut or modify the back of the clock case I've so I'm looking at possible "repair".

My initial thoughts were that the battery contacts were intermittent - the battery contacts are sandwiched between the movement main plastic housing and the copper side of the circuit board, so I soldered short lengths of wire directly to the circuit board battery contacts from the battery housing terminals, the movement was however still losing time.
There is a trimmer capacitor on the board, the crystal is a 4.194304mhz unit so a divide by 2, 22 times would give the required 1 sec timing pulse to the movement motor, I checked the crystal with my scope and the period was around 238.4 nS which is close to 4.194304mhz, I have adjusted the capacitor and so far the movement seems to be keeping good time using my mob phone as a reference, there is a few minutes of backlash in the gears so when the minute hand is at the 3 position it will show slightly fast and at the 9 it will show slightly slow, if I can get the movement to gain no more than 15 or so seconds a week I'll be happy, by the time daylight saving changeover arrives it will only be a few minutes out.

This brings me to my question - why have a trimmer capacitor at all, surely if the crystal is running at the design frequency then it would not need to be trimmed, am I expecting too much from the crystal?

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Cousins sell them also I have used this company a few times https://www.clockparts.co.uk/index.html#menu

Whilst on quartz clocks I was asked to look at a Westminster quartz pendulum clock because it had always chimed incorrectly ie 10mins past the quarters & 5mins before the hour. Solution removed the battery moved the hands (using the adjusting knob) to 05:50 inserted the battery again and moved to the correct time again using the adjusting knob and now it is spot on.  

 

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Hi  with any electro mechanical device like a clock, especially a quartz clock where the gears are formed by injection moulding, here is always going to be some variation , hence the trimmer on the electronics to compensate. Hermle movements along with Seiko, Herchinger and Junghans are pretty good movements the cheaper ones are as manufactured and the discrepencies are compensated using component values.  Newgeneration clocks are a good source.

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