Hi All ,
I have a clock that strikes every hour and is suppose to chime , so every hour i am getting a pulse but the chime does not go off , if i hold the contact manually for a split second longer then it catches it and chimes but when the hour comes around and hits the contact it pulses to fast and does not pick it up . it is a 3 volt signal and i didnt know would it be possible to use a capacitor and transistor or some kind of circuit to lengthen that pulse or a circuit to catch that high speed pulse and send out its own longer 3volt pulse ?

 

Hi All ,
I have a clock that strikes every hour and is suppose to chime , so every hour i am getting a pulse but the chime does not go off , if i hold the contact manually for a split second longer then it catches it and chimes but when the hour comes around and hits the contact it pulses to fast and does not pick it up . it is a 3 volt signal and i didnt know would it be possible to use a capacitor and transistor or some kind of circuit to lengthen that pulse or a circuit to catch that high speed pulse and send out its own longer 3volt pulse ?

Do you have a schematic, or at least good photos of the front and back of the PCB?

 

Sounds like the contact is activated mechanically. Can you modify this mechanism to add delay?
SG

 

Yaakov , No i do not have a schematic or pictures but i am at work and could try to get pictures tomarrow ,

sghioto , Yes it is mechanically activated , lets say there is a left tab and right tab , gear turns ccw and peg catches left tab and pulls it left until it slides off of peg and springs over against and then away from the right tab for a split second , sorry for the crude explanation but i dont see how i can modify that without changing the timing of when the chime goes off .

 

Pictures would help a great deal. Also, of the chime activating mechanism.

I suspect your problem is mechanical, not electronic, but the solution might be electronic anyway.

 

It could be as simple as adding a resistor and capacitor at the contact output.

 

i dont see how i can modify that without changing the timing of when the chime goes off .

Did this chime ever work properly?
SG

 

I will try to get pictures , and i already did mess with the contacts a good bit but it doesnt make a differance , and i know it is making contact as i used the contact to pulse an LED and that worked . and yes it used to work then it sometimes worked now it never works .

 

How does the “tab” return to its original position after being moved by the “cog”?

If there’s a spring, perhaps you could find a replacement spring that is weaker. One way to find such a spring is to measure the length of the spring when at rest, the number of turns AND measure the diameter of the wire used to make the spring.

What you want is a replacement spring of the same length at rest, the same number of coils AND of a thinner diameter wire. You could also try a spring of the same length BUT with fewer coils.

Basically, I’m proposing that replacing the existing spring with a weaker one, will increase the return time, lengthening the pulse.

This is all theory, but may be worth a try. One or two springs isn’t likely to break the bank.

 

Have you cleaned the mechanism? A build up of dust over the years can make it sticky. It may have originally had some sort of lubricant. often carbon dust, like used in locks can help. If it used to work, I;d be more inclined to try to fix it, not modify to fix a symptom.

 

It is a thin long tab , so the tab itself is the spring , I do have pictures now but i can not figure out how to upload as it says they are too large .
and yes i tried cleaning them and i agree i would rather fix the problem then add circuitry to support the failing circuit , I feel part of the circuit is getting week and is no longer able to catch that fast of a pulse , but i could be mistaken , and the problem is it is an old clock that you cannot get repacement boards for that im aware of but they want me to fix it because of the songs that this clock has that newer ones dont .

 

 

 

here are some pictures now , CN7 is where the 2 wires go to the contact , you can do the same thing right by the connector , if you touch it too fast with a jumper it wont go but if you pulse it slower then it will , i considered hooking up an ardiuno and playing with the timing and seeing exactly how long it needs to pulse but that wont fix anything other then curiousity on the reverse side of the board CN7 is between the R28 and R25 print .

 

What happens if the contact is held closed for awhile, then opened? Is it possible that is the signal? That is, the contacts are normally closed and opening activates the chime.

Your picture shows the contact apparently open when the top contact is in the groove. If the cogged wheel turns clockwise, it would tend to push the contacts closed on the rising edge. If CCW, the opposite would happen.

Does the cogged wheel turn CW of CCW looking at it from the picture's perspective?

 

the wheel turns ccw and has a peg on the bottom side that catches the left contact once every turn , and pulls it away about 2-3mm and lets it snap against the right contact , i hooked up an LED to the contact and my own power supply and the LED does flash when i turn the wheel one revolution . the contacts are normally open . actually now i reread your post , you are saying it should maybe be nc contact then when you break it activates ? i think you are right ! i will try that when i get home tonight , i never thought of it from that angle .

 

From the photo it appears that capacitor C57 is directly across the contact. You might try replacing it.
SG

 

I think jpanhalt had a good point and is probably right so i will try that and if that doesnt work then i will try replacing C57 , thanks for you guys help and ill let you know how it turns out .

 

This is so obvious, but have you cleaned the contact? Contact cleaner or alcohol? If the contact has become pitted over time, maybe you can polish them with an ink eraser. Just be careful not to permanently bend the contact leaf.

 

yes i tried to clean them , they did look pretty good tho but i took a small piece of scotch brite and tried to polish it up a bit , is that too abrasive ? i never thought of an eraser, thanks for the suggestion .