Citizen Cosmotron X8 04-4800 Fault finding

[Simeon]

I took a chance on a non running Cosmotron X8 ("perhaps just needs a new battery" said the advert).

Sure enough, I open it up and it has the wrong battery installed (a Renata 344 rather than the correct Renata 386) and the screws holding the battery contact had been sheared off to half a head on both ends. Ho ho, I thought - there's the problem.

I got the broken screws out easily enough and as soon as I placed the correct battery in place the balance started. This picked up speed when I reinstalled one side of the battery contact and looked like it was a runner. As I was trying to get the replacement screws in, I did one side but the second was a bit of struggle (hold down the battery contact against its spring while dropping the screw in with tweezers) the balance stopped again. This time it wouldn't start again. 98 percent sure that I didn't stick anything, anywhere important or break it in a mechanical way. The battery was in place for most of the struggling with the contact, so it might have had an intermittent connection which could have upset the electronics.

I tried giving it a puff with the blower but the balance doesn't seem to rotate in the normal way, it seems to be held in a static position by magnet. It can be pulled out of this position but spins back and stops dead. This may well be correct for all I know.

Anyway, does anyone know anything about these watches and can tell me how I would go about and fault find this?

I will be servicing it at some point so should be able to rule out mechanical issues from an old watch but not sure where to start with the electrical part of it.

[rjenkinsgb]

See around 2/3 of the way down this page, about battery fitting problems?

https://adventuresinamateurwatchfettling.com/2023/12/26/the-worlds-first-transistorised-electronic-balance-movement-the-citizen-cosmotron-x8/

 

 

[Simeon]

On 5/17/2024 at 6:06 PM, rjenkinsgb said:

See around 2/3 of the way down this page, about battery fitting problems?

https://adventuresinamateurwatchfettling.com/2023/12/26/the-worlds-first-transistorised-electronic-balance-movement-the-citizen-cosmotron-x8/

 

 

Thank you that was an interesting article. I definitely could have pushed the battery in too hard, thus shorting it out on the case. The 'switch' on the keyless works is another possible candidate as the movement is slightly loose in the case and something on the dial side could be shorting as well. I will probably need to dive in to giving it a service and try and overcome some of the problems as the article author did. 

[rjenkinsgb]

I don't know if its pushing it in too far, but because the available batteries do not have a raised contact, clear of the case? 

I'm not keen on the idea of soldering to a battery, but possibly stick a small washer or similar metal spacer on with conductive paint or adhesive, plus a nylon washer around it?

 

Edited May 19, 2024 by rjenkinsgb

[Simeon]

OK, I fixed it. There was a combination of factors.

 

First I bent the wings on the small, star like, battery contact to be a bit more erect and give a better contact. This is located within a thin plastic sheet that is snapped into place in a groove between the bridge and the main plate. Underneath this was the "switch" contact with a plastic end that moves with the yoke that turns the movement on and off. This had all got a bit displaced and was not moving with the yoke, so I carefully refitted the star contact and its plastic sheet and making sure that I could see the switch contact making good connection (you can see through a small hole on the dial side). Refitted the battery and off it went! The switch works fine to turn it off / hack the seconds but there is always a momentary pause, I guess as the magnetic field builds up when you start it up again. 

 

I am going to let it run for a bit and then regulate it. It appears to be running 30 sec per day fast at the moment.