texas instruments-malfuctioning module

[steveh]

Hi Folks

I'm a newbie having just joined, so hello to everyone (couldnt see an intro bit to the site). I've been obsessed with led watches ever since getting a trafalgar led for my 10th birthday (in 1977). I've a sinclair black watch I'm currently doing battle with-yes its the battery connection, works perfectly otherwise.

My question is, I've a starwars texas instruments. It only lights up one digit (the last digit on the right) with a 1, is there anything I could do to fix it?

be grateful for any advice

cheers

Steve

[Led-Time]

Hi Steve,

Welcome to the forum its good to see another Scottish member interested in LED's.

Your single digit problem is one I've come across a few times with Texas watches it needs a new quartz crystal fitted, Maplins electronic stores sell them for around 50p its just a case of removing the old crystal and soldering in the new one. A fine tip soldering iron is needed as the contacts on the Texas module are tiny.

If you need any help give me a shout...

[steveh]

Hi Klippie

thanks for reply, I live near Maplins so I'll nip out and get one later. I used to be able to pick up a few Led watches from either the Barra's in Glasgow or paddy's market. Not seen any for a while though.

I'll let you know how I get on

cheers

Steve

[steveh]

Hi Klippie

Well, I bought a new crystal, 47p! I've soldered it in but the module is still showing a 1, is there a polarity to the crystal?

thanks

Steve

[Led-Time]

The crystal can be fitted in any way round, the single lit digit is the usual indication of a faulty Q.C. it was worth a try for 47p. Is there any sign of battery corrosion on the module tracks and contacts.

[steveh]

Hi there

No, it's really clean, I can't fully dismantle the module as it's glued together. I'm using a module tester, do I need a third lead to test the buttons?

cheers

Steve

[Led-Time]

Depending on which type of module fitted the more common one has the button contacts combined with the clip that holds the batteries in so its just a matter of pressing the spring part to the little contact on the module to show the functions, but if the display is constantly showing a single digit that won't help. I can't remember off hand if the module has a trimmer if it does a faulty one may also cause the same problem.

[steveh]

Hi Klippie

yes, it does have a trimmer-is this a variable resistor to keep the crystal in check? can they be bought as per the maplin crystal?

cheers for replies- I'm learning a lot

Steve

[rewolf]

The trimmer is not a resistor, but a capacitor.
22pF would be a good choice http://www.maplin.co.uk/Module.aspx?ModuleNo=460 - but I doubt it will fit into the watch.
To see if it works you can replace the trimmer with a 15~22pF ceramic capacitor.

[steveh]

Hi Rewolf

thanks for advice, I'll try that

cheers

Steve

[Led-Time]

Before you change the capacitor try something first, put the watch in the fridge for about 30mins then check to see if it works, if not get a hair dryer and gently heat it but not roasting hot again check to see if it works, its a long shot but its worked in the past for me several times

If changing the capacitor gets it working and you have a few dead modules kicking around try a trimmer from one of them.

I meant to ask is it always the same digit that lights up.

.

[steveh]

Hi Klippie

yes, always the same digit. It is most probably knackered but i fancied having a tinker. I've got 3 working led watches, it just irritates me though that I can't get this one working.

I'll try the fridge and a bit of heat.

Thanks for all help

cheers

Steve

[Led-Time]

How did you get on with the heating/cooling cycles.

[steveh]

Hi Kiippie

tried it in the fridge, just the same, a 1 lights up on the last segment. Don't have a hairdryer but tried it on a radiator, still the same, I guess I need to try a capacitor. Maybe it's just beyond repair. Shame it's glued together, perhaps there's a short somewhere.

Thanks for all help thus far

Steve