National Semi Conductor calculator watch

[767Geoff]

Just received the watch and did the following:

Disassembled the movement and case. Removed the LCD panel, cleaned all contacts on the PCA and LCD panel. Resurfaced the brushed finish (pictures to follow).

Now to the meat of the post. This watch suffers from the dreaded temperature related darkening disease. The LCD panel is crisp and clear when off the wrist and at room temperature or below. Strap it to the wrist and the display darkens. This is the same darkening that occurs when you heat an LCD display with a hair dryer. Normal display will return to the clear display as the heat dissipates.

Unfortunately as the LCD panel ages the temperature range for a clear display reduces until 98.6 'F (body temp) becomes to high .

Placing this watch in the fridge for a few minutes or leaving the watch at room temperature and it is perfect.

I know the only repair is for a new panel to be installed. So, anybody experimented as to a fix for this or does anyone have a source or replacement idea. What is the science behind the darkening, could it have something to do with the polarizer film degenerating (don't see how but)? How difficult to get an LCD manufactured in a lot of 100? Would there be a demand for a new LCD panel replacement?

So many questions.

Cheers. geoff

P.s. Watch runs and looks good on display, at room temperature, just not on wrist. Would work well on somebody with an artificial limb

[Old Tom]

The darkening is caused by the liquid crystal material melting and reverting to the non-nematic liquid state- in other words, the LQ loses it's power to twist the plane of transmitted light so all you see is the lack of light after passing through the two crossed polarisers. Usual cause of this melting point shift is impurities in the panel sealant which poison the LQ material (99.5% of "bleed" is a actually this sort of decay in the liquid crystal) and then spreads through the panel fairly rapidly in old wide spaced panels ( I suspect the process may be auto-catalytic in nature given how quickly panels can fail).

[767Geoff]

Thais Tom.

So it would seem that this calc watch is destined to fail, as with all aging electronics, even if not in use. As I said, it works at the moment off the wrist at room temperature, unfortunate as it is an interesting watch.

Interesting that the temperature reduced temporarily results in a clean display. If I could only hook up a cooling system to the watch, or better yet, come up with a replacement. Looking through the the web I don't see any 6 digit displays with decimal points on any vintage panels.



Cheers, Geoff

[Adam]

Geoff

Could you use some insulation between you and the watch case? An experiment, see how much insulation you have to add before the watch works for at least half an hour. Even if its just for the forums amusement, photos a must of course.


Adam

[rewolf]

How difficult to get an LCD manufactured in a lot of 100? Would there be a demand for a new LCD panel replacement?

Not too difficult. Given the segment layout and voltage needs, any chinese LCD manufacturer could probably do this. But you'd have to pay initial cost and tooling.

[wzy-hman]

As well as initial tooling etc costs you would also need to commit to a certain minimum volume which is where the total cost can end up quite expensive even though on a per unit basis it might be reasonable

[767Geoff]

Thanks for the responses!

Soooo, I get to Hong Kong, Shanghai and Beijing. How would I go about finding a manufacturer there? Anyone with experience? How many units would be a minimum order and would there be a market for replacing the LCDS for this particular watch?

Geoff

[SASM]

You have to go to Guangzhou / Shenzhen which is quite a bit like the chinese sillicon valley. Typically a minimum order are 10000 pcs.

[rewolf]

Probably not so many.
At work we sometimes have custom LCDs made, from a few hundred to several tenthousand per year. We don't deal directly with the manufacturers, but with a local distributor here in Germany. We don't even know the actual manufacturer. Sometimes it even happens that a project is cancelled after a few prototypes. We never had to make any commitment.

Is there a market for a replacement LCD? I don't know. Personally, I'm not that much interested, as the LCD in my NSC calculator ist still working fine .
Say one gets 20 LCDs made in a prototype run. Including initial cost this amounts to 100-200$ per LCD. Maybe worth it, considering the price difference between working and non-working.

[Old Tom]

Didn't the chap at rawsar.com have new LCD panels made for Heuer Chronosplit watches? I seem to rmember him posting here about two years ago and it may be worth while contacting him about the process/costs involved.