Vintage Tissot digital watch help needed

[jimmy74]

Hi I have what seems to be one of the very first digital Tissot watches made back in the late 60's or early 70's. It has a very simple LCD display and what I guess is the model number on the rear 1785 and on the inside of the rear plate are printed the numbers 50.12.8. The watch doesn't work anymore and taking the rear plate off I can see what seems to be a broken SMD component which is however screwed on both ends (not soldered) to the PCB. This fact leads me to think that maybe it is some sort of fuse. I would like to know if anyone here can help me out in getting this watch working again, I have already tried contacting Tissot but no reply whatsoever and retailers are unable to help me.

A schematic I suppose would be impossible to find but I can post some photos and maybe someone can tell me what that broken part is and what to replace it with. Any help at all would be much appreciated.

thanks
J.

[bucko170]

Welcome to the forum J

The first steps would be to post the photo's so the experts here can have a look and see how to assist you further.

[charger105]

It's very difficult to give any help without pictures, but at a guess, is it similar to the Tissot resurrected here:

viewtopic.php?f=64&t=4894

If so, then it's a screw-down capacitor.
If it is this module, read throuth the thread, it'll probably give you some ideas.
Rgds.

[jimmy74]

Yes that circuit PCB seems to be exactly the same as the one in my watch, so that part is a screw down capacitor, I'll have to ask the person who wrote up that post where to find a cap like that. My watch has a different shaped metal casing but the functions, PCB and LCD display seem to be exactly the same.

thanks
J.

[Old Tom]

Sounds like one of the NEC moduled Tissots from 1975- they share these modules with Casio and a few other brands. If your module is working it should still run even with the screw in capacitor broken or removed- it is a very small value capacitor used to correct the rate at which the watch runs and they were individually selected for each module at time of assembly. Don't forget to reset the watch by shorting the AC terminal (just to the side of the battery compartment) to battery positive- clears all the dividers and registers and stops the watch locking up.

[jimmy74]

Thanks Oldtom, I am no expert in digital watches so I have no idea where the AC terminal is. The watch wasn't working the last time I tried with a new battery some 20 years ago or so and has been sitting in my drawer ever since.
I pulled it out and took the rear cover off a week ago and contacted Tissot without any luck and this morning I registered to this site. So if the watch is supposed to work even with that cap cracked and the missing screw then I suppose there's something else that need fixing.

J.

[Kasper]

Hi Jimmy and welcome to the forum,

could you add your country in your personal prefs..easier for people to help you.

a few shots of the watch could do miracles.

[jimmy74]

Some photos here:

http://www.flickr.com/photos/73835524@N00/8383322217/in/photostream
http://www.flickr.com/photos/73835524@N00/8384406652/in/photostream
http://www.flickr.com/photos/73835524@N00/8383322877/in/photostream

[charger105]

Looks like the positive battery contact is missing.
When you put the battery in, the main battery casing (the positive terminal) must be contacting somewhere on the module.
In yours, it isn't touching anything. The little screw hole next to the battery compartment should have a contactor in it, which makes this connection.

Could be a real easy fix
Rgds.

[jimmy74]

Thanks charger, that's what I thought.... how do I go about fixing it? Also what sort of battery do I need?

thanks
J.

[Old Tom]

The correct battery for that module (Casio QW-01 or QW-04- that one looks to be marked as an 01) is a 301 (386 is same size but has a flat negative terminal). Looking at the photo I am not sure whether that module will run (I originally, pre-photo, thought it was a later one) as the small "capacitor" seems to be series connected with the crystal and trimmer so a break will stop the oscillator running. You could make a replacement with a small SMD capacitor and the original component loops (!)- not as hard as you would think if you make a small jig to hold the loops and use Silver epoxy to attach the capacitor.