Hi friend needs an advice on this:

This Citizen Transistor wall clock works great! But sometimes it run little fast or slow. I found its circuit as below

In another forum I found the following solution: adding a diode and resister as I mentioned in the diagram to minimize the reverse voltage pulse when the transistor turns off.

will it work ? and is it necessary ? because its not in the original design

 

Most battery operated clocks use a crystal oscillator for the timing, so I don't see how that modification can help.

 

Likely the reason why it sometimes runs fast and sometimes runs slow may be due to temperature variations. You'd need a much more complicated circuit to compensate for temperature drift.

 

Look at the back of the clock and you should find a little black knob for adjusting the speed.

 

thanks all for your advice. This is not a crystal oscillator clock , This is a transistorize clock ! even though it's simple, its working very well since 30Years!...here what i need to know electronically is : whether this modification is correct ! make any seance theoretically. further, does it make any reverse voltage pulse as it say , and how it effect ?

 

What is the function of the little white knob on the right?
Isn't that a speed adjustment?

 

What is the function of the little white knob on the right?
Isn't that a speed adjustment?

yes! its for speed adjustment. even though speed is corrected with it ... after few months it happen again...

just forget the this adjustment things .. what i need to know is theory behind the adding of this diode and the resister.

Or.. will adding these two make any new issue ??

 

I would say the speed is altered by the tension on the escapement spring,less tension will slow it down.

 

I would say the speed is altered by the tension on the escapement spring,less tension will slow it down.

that's correct 100%.... but i want to know the theory behind the adding of this diode and the resister.

Or.. will adding these two make any new issue ??

 

i want to know the theory behind the adding of this diode and the resister.

It may help protect the transistor, but I don't seem how it can help improve the clock accuracy, which is primarily a function of the mechanical escapement.

What about replacing that old mechanical mechanism with a modern crystal controlled one such as one of these? That should solve the accuracy drift problem.

Edit: How is the day-date mechanism controlled?

 

It may help protect the transistor, but I don't seem how it can help improve the clock accuracy, which is primarily a function of the mechanical escapement.

What about replacing that old mechanical mechanism with a modern crystal controlled one such as one of these? That should solve the accuracy drift problem.

Edit: How is the day-date mechanism controlled?

Thank for the information. Yes you are correct. crystal controlled set will work fine. however i needed to know on this addition. does adding these 2 parts drain the battery quickly ?

Is it better to replace C828 transistor with a BC549 ??

This is How is the day-date mechanism controlled?

 

The diode and resistor are there for voltage spike supression when the transistor switches off at each oscillation period of the escapement. Depending on the coil inductance and the voltage breakdown rating of the transistor, they may or may not be necessary. If the clock has been working for years without them, then clearly they are not necessary. They will do nothing to improve the clock accuracy, but will not drain the battery unless the diode is faulty.

 

thanks all for your advice. This is not a crystal oscillator clock , This is a transistorize clock ! even though it's simple, its working very well since 30Years!...here what i need to know electronically is : whether this modification is correct ! make any seance theoretically. further, does it make any reverse voltage pulse as it say , and how it effect ?

The thing is 30 years old. Things wear our. Gears wear out and warp. Time for a new clock (pun intended). It isn't like this is a 200 year old time piece that is worth saving. Toss it and buy a new one.

 

This is How is the day-date mechanism controlled?

So is there appears to be a mechanical connection between the clock mechanism and the day-date mechanism.
Would that be disrupted if you changed the clock mechanism?

 

It looks to me to be a Collpits oscillator I would try replacing the electrolytic capacitors first. After 30 years they are probably dried out, then see what happens.

 

It looks to me to be a Collpits oscillator I would try replacing the electrolytic capacitors first. After 30 years they are probably dried out, then see what happens.

You are correct ! I did replaced all electronics parts including the Capacitors

Is it better to replace C828 transistor with a BC549 ??

Meanwhile pls tell me the purpose of the 150K transistor ? is it a bleeding Tr ?? (I'm try to understand some theory part from you masters ..pls help me )

 

Seems that the clock timekeeping is based on an electro-mechanical oscillator.

The function of the drive circuit is to replace energy lost due to friction and work done to move the hands, etc.
The drive has no part in determining the time constant of the oscillation.

You will not have much luck twiddling with the drive circuit, adjust the torsion spring in the oscillator, this determines the frequency.

 

Seems that the clock timekeeping is based on an electro-mechanical oscillator.

The function of the drive circuit is to replace energy lost due to friction and work done to move the hands, etc.
The drive has no part in determining the time constant of the oscillation.

You will not have much luck twiddling with the drive circuit, adjust the torsion spring in the oscillator, this determines the frequency.

Thanks!

as I told, i dont need to fix the issue--and its not a big issue too. But i need to know that what happen when diode and resister are added

 

It will damp the back emf from the coil, and probably prevent it from discharging the 220nF cap, But your pcb shows Two electrolytic caps!! .

so it may increase the time between pulses and hence slow the clock down it won't drain the battery , Try it and see.

 

It will damp the back emf from the coil, and probably prevent it from discharging the 220nF cap, But your pcb shows Two electrolytic caps!! .

so it may increase the time between pulses and hence slow the clock down , personally i think it will, Try it and see.

excellent ! actually the diagram is correct! there is one electrolytic 10Uf and one ceramic 220nF. The pic i have attached herewith is not my one , i found the similar one from internet.

Is it better to replace C828 transistor with a BC549 ??
Meanwhile pls tell me the purpose of the 150K transistor ? is it a bleeding Tr ??

here is the my one