CompuChron problem

[Stevato]

Hi all,

My CompuChron still worked fine a few months ago when I checked it. Today, I checked and it did not turn on.

[Kasper]

viewtopic.php?f=64&t=2584&p=15369&hilit=faint+leds#p15369 check it out

[Stevato]

http://www.newdwf.com/viewtopic.php?f=64&t=2584&p=15369&hilit=faint+leds#p15369 check it out

I have to admit that I don't get the idea after checking the link. I am a real newbie.

Thank you anyway Kasper!

[767Geoff]

Nice avatar!

As with photography light meters based on cadmium sulphide their resistance builds over time. That means 'dim mode' is always on.

This was a battery saving mechanism. In strong light the resistance of the cadmium sulphide sensor is low allowing max current to the LEDs translating into brighter display. In low light the resistance increases reducing the current to the LEDs. You don't need bright displays at night and therefore battery savings.

Cadmium sulphide oxidizes over time. Never buy an old light meter for the same reason, except for display!

Cheers, Geoff

Unfortunately and sadly, most electronic components decay over time. I love transistor radios from the 60's. you can get fantastic reverse painted 6 - 9 transistor pocket radios cheap due to dried out capacitors. Replace the old caps,and the radio is back on line.

[bucko170]

The good news is that if the light sensor is at fault a 'workaround' repair is available "usual repair is to solder a 1K SMD resistor in place of the cell and always run at full brightness"

Before going down this path I would spend a couple of minutes cleaning up the battery contact points and make sure your watch man is using silver oxide batteries.

[s_elias]

This is a great tip. Do all LED watch modules have the photo-resistor / sensor? I didn't think NS (national semiconductor) modules had one.

I guess if they did, it would have to be visible (near) the window / glass - right?

Can someone upload a picture of one so we know what to look for?

Thanks

[bucko170]

There is a photo on this site which marks out the light sensor on a Pulsar module http://ledwatch.net/_wsn/page4.html

I don't recall any NSC modules having a light sensor, the Compuchron above has a Sanyo module.

The Sanyo light sensor is just above the display.....

[bruce wegmann]

This is exactly the same part used on the Pulsar modules. Sanyo also supplied the green LED displays used on the CompuChron and 3416 Pulsar models (Litronix, Monsanto, and Hughes supplied red displays).

[Stevato]

Thank you all for your advices and comments.

[bucko170]

Clean all the contact points that the batteries touch including those on the case back to ensure that the power from the batteries is reaching where it should....



The best tool I find to clean the contacts is a fibreglassed tipped pen see here for example http://www.ebay.com/itm/Economy-Fibergl ... 4849f9ae3f

Put a little isopropyl (rubbing alcohol) on a Q-Tip and give the contacts a wipe, see here http://www.ebay.com/itm/Mg-Chemicals-82 ... 1e76f9113a allow to dry before trying the batteries.

[bucko170]

Also clean the button contacts at the side of the module, the inside of command buttons and the battery clip to ensure that you are getting a good contact to the module from the command buttons.

[bucko170]

If you are not confident doing this I am sure some of the forum members that are local to you will be able to help you out, cleaning the contacts is as far as my technical ability takes me, if this does not resolve the issue I am sure someone else will be able to take things further for you.

BTW: It would also be worthwhile checking that the set/command buttons are not sticking and activating the display.

[bruce wegmann]

This is the kind of scrambled, incomplete display I often see on Pulsar modules that have been corroded, or zapped by static electricity. It is clear the the driver logic is not working correctly. If I had to guess, I'd say this module is a goner. Wouldn't be unhappy to be proved wrong, though.

[BENRUS]

This is the kind of scrambled, incomplete display I often see on Pulsar modules that have been corroded, or zapped by static electricity. It is clear the the driver logic is not working correctly. If I had to guess, I'd say this module is a goner. Wouldn't be unhappy to be proved wrong, though.

I've had a few Pulsars that acted like this, and they were for sure goners.
HEAT made some work properly (untill they cooled down after a minute)
If you see that your display is a bit scrambled or not trying to display the time at all (not just a dim display), It may need more than a battery contact cleaned.

[Stevato]

Clean all the contact points that the batteries touch including those on the case back to ensure that the power from the batteries is reaching where it should....

The best tool I find to clean the contacts is a fibreglassed tipped pen see here for example http://www.ebay.com/itm/Economy-Fibergl ... 4849f9ae3f

Put a little isopropyl (rubbing alcohol) on a Q-Tip and give the contacts a wipe, see here http://www.ebay.com/itm/Mg-Chemicals-82 ... 1e76f9113a allow to dry before trying the batteries.

Thank you very much for your help.

[Stevato]

This is the kind of scrambled, incomplete display I often see on Pulsar modules that have been corroded, or zapped by static electricity. It is clear the the driver logic is not working correctly. If I had to guess, I'd say this module is a goner. Wouldn't be unhappy to be proved wrong, though.

I've had a few Pulsars that acted like this, and they were for sure goners.
HEAT made some work properly (untill they cooled down after a minute)
If you see that your display is a bit scrambled or not trying to display the time at all (not just a dim display), It may need more than a battery contact cleaned.

That is exactly what I've been worrying about.

[coconutman351]

I've had my Wittnauer Polara watch go dim on me and it was resolved by carefully cleaning the button contracts and battery terminal and adding NEW set of 357 batteries. Now when I say dim, while pressing the time button the display varied in intensity like a flickering florescent bulb so I knew the logic board was functioning fine. Unlike the Pulsar's with the magnetic reed switches, these "newer" LED watches have issues with the physical metal contacts as they oxidize over time. I assume they utilized this design to reduce production costs and the hassles of paring reed switches with the Pulsar case buttons. I agree with Bruce though, if the display is not showing any signs of the logic board working then you might have a module that may have been zapped during the batter changing process. It is extremely important to ground yourself when you open the watch case to change your batteries or handle your module, especially with the earlier LED modules as the chips were less resilient to static discharges. Good luck in your effort to revive the module, I really like the segmented LED display.

[bucko170]

I am forever an optimist and think where there is life there is hope, it was working beforehand so don't give up just yet, clean up the contacts, cross your fingers and hope for a positive outcome.

[coconutman351]

Another thought. Sometimes over the years solder joints become brittle and may fracture just enough to cause an intermittent contact and the effect could be the result of a dimmed display. If it is possible to power up the module outside of the case see if you can lightly tap around the module with a non-conductive stick. If the display lights up brightly and works zero in on the defective solder joint that may be the cause of your watch problem. Hope this helps.