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From: Joe on 7 Aug 2010 20:05
I have a Radio Shack count-up/count-down timer, catalog #63-878. It's
about 2.5"x3.2"x0.70" thick.

It's around 10 years old and some of the input keys had become sticky.

I had to remove the back, then remove the circuit board which was held in
by four screws.

As I gingerly removed the circuit board, the LCD display just fell off the
circuit board. I cleaned some liquidy gunk from the circuit board and the
rubber-membrane keys, and re-assembled the timer.

The display has what looks like a rubber strip on the bottom edge which
contacts about 12 gold plated pads on the circuit board. The contacts are
just lying flat on the circuit board - they are not edge connectors.

The four screws that hold the circuit board to the case also seem to make
the circuit board press tightly against the rubber strip on the bottom of
the LCD.

After re-assembly, the timer works.

I'm glad it didn't have a ribbon cable because they seem to be so fragile.

BUT.. how is contact made from the circuit board to that LCD?

--- Joe
From: Jeffrey Angus on 7 Aug 2010 20:54
On 8/7/2010 7:05 PM, Joe wrote:
> BUT.. how is contact made from the circuit board to that LCD?

That rubber strip has a lot of conductive strands that
make contact with the gold pads on the circuit board
and the contacts on the edge of the LCD display.

Visually, think of it like a strip of corrugated cardboard
on edge with little bits of wire in each corrugation. ;-)

Jeff
From: Arfa Daily on 7 Aug 2010 21:08


"Joe" <none(a)given.now> wrote in message
news:none-0708101705410001(a)dialup-4.231.173.102.dial1.losangeles1.level3.net...
> I have a Radio Shack count-up/count-down timer, catalog #63-878. It's
> about 2.5"x3.2"x0.70" thick.
>
> It's around 10 years old and some of the input keys had become sticky.
>
> I had to remove the back, then remove the circuit board which was held in
> by four screws.
>
> As I gingerly removed the circuit board, the LCD display just fell off the
> circuit board. I cleaned some liquidy gunk from the circuit board and the
> rubber-membrane keys, and re-assembled the timer.
>
> The display has what looks like a rubber strip on the bottom edge which
> contacts about 12 gold plated pads on the circuit board. The contacts are
> just lying flat on the circuit board - they are not edge connectors.
>
> The four screws that hold the circuit board to the case also seem to make
> the circuit board press tightly against the rubber strip on the bottom of
> the LCD.
>
> After re-assembly, the timer works.
>
> I'm glad it didn't have a ribbon cable because they seem to be so fragile.
>
> BUT.. how is contact made from the circuit board to that LCD?
>
> --- Joe

It's known as zebra strip. It's a sandwich of hundreds of tiny regular
rubber strips, alternated with hundreds of conductive rubber strips.
Compared to the sizes of the gold-plated print lozenges that form the
connection points, and the spaces between them, several conductive strips
will lie on each lozenge, and at least a couple of regular rubber insulating
strips, will be in the gaps. When the whole caboosh is tightly fixed
together, the conductive strips join the PCB lozenges to the deposited metal
connections on the LCD glass.

Have a look at

http://www.densitron.com/displays/content.aspx?id=808

Arfa

From: Jasen Betts on 8 Aug 2010 09:22
On 2010-08-08, Joe <none(a)given.now> wrote:

>
> The four screws that hold the circuit board to the case also seem to make
> the circuit board press tightly against the rubber strip on the bottom of
> the LCD.
....
> BUT.. how is contact made from the circuit board to that LCD?

It's that rubber.

It's made of of axially stacked layers of conductive and non-conductive
elastomer. google "zebra strip" for more info.


--- news://freenews.netfront.net/ - complaints: news(a)netfront.net ---
From: Joe on 9 Aug 2010 02:15
In article
<none-0708101705410001(a)dialup-4.231.173.102.dial1.losangeles1.level3.net>,
none(a)given.now (Joe) wrote:

> I have a Radio Shack count-up/count-down timer, catalog #63-878. It's
> about 2.5"x3.2"x0.70" thick.
>
> It's around 10 years old and some of the input keys had become sticky.
>
> I had to remove the back, then remove the circuit board which was held in
> by four screws.
>
> As I gingerly removed the circuit board, the LCD display just fell off the
> circuit board. I cleaned some liquidy gunk from the circuit board and the
> rubber-membrane keys, and re-assembled the timer.
>
> The display has what looks like a rubber strip on the bottom edge which
> contacts about 12 gold plated pads on the circuit board. The contacts are
> just lying flat on the circuit board - they are not edge connectors.
>
> The four screws that hold the circuit board to the case also seem to make
> the circuit board press tightly against the rubber strip on the bottom of
> the LCD.
>
> After re-assembly, the timer works.
>
> I'm glad it didn't have a ribbon cable because they seem to be so fragile.
>
> BUT.. how is contact made from the circuit board to that LCD?
>
> --- Joe

Thanks for the helpful info, folks. I had never heard of a "zebra strip"
and with my eyes there was no visible indication of conductively separated
segments on that rubber strip.

--- Joe
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