I have a [1.5 X .75 inch] 4 digit + sidebar and bottom bar LCD [?] display
on my exercise machine which is "ghosting" some of the numbers.

I disassembeled the unit and was surprised that the LCD is not wired or
cabled onto the board.

Rather, the thin glass screen simply pressure fits with a flexible strip
sandwiched between the glass and the contacts on the PC board.
The strip appears to be flexible silicone with a series of tiny "black dots"
running down the middle.

There is no electrical contact that I can see. Not sure if the "black dots"
are LEDS or what. But they mate to pure glass on the screen side.

I cleaned the contact areas [glass and electrical] and it all snapped back
together OK but the "ghosting" persists.

Is there a better way to clean this?
What, exactly, are the "black dots"?

Thanks for any comments.


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"John Keiser" wrote in message
news:5r7kf.119$Bs2.64@trnddc01...
I have a [1.5 X .75 inch] 4 digit + sidebar and bottom bar LCD [?] display
on my exercise machine which is "ghosting" some of the numbers.

I disassembeled the unit and was surprised that the LCD is not wired or
cabled onto the board.

Rather, the thin glass screen simply pressure fits with a flexible strip
sandwiched between the glass and the contacts on the PC board.
The strip appears to be flexible silicone with a series of tiny "black
dots" running down the middle.

There is no electrical contact that I can see. Not sure if the "black
dots" are LEDS or what. But they mate to pure glass on the screen side.

I cleaned the contact areas [glass and electrical] and it all snapped back
together OK but the "ghosting" persists.

Is there a better way to clean this?
What, exactly, are the "black dots"?

Thanks for any comments.


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What you have there is a conductive rubber sandwich, and it's the common way
to connect an LCD panel to a PCB. Usually, the sandwich is a ' comb ' of
alternate black conducting rubber fingers, and white insulating ones,
although there are variations - sounds like you've got a slight one there.
If you look very closely at the glass panel, maybe under a strong lamp, you
will see that there are semitransparent corresponding fingers, although at a
wider pitch, on the glass.

These are a form of metallisation deposited on the glass, and are the
continuation of the actual digit electrodes, which in the case of the upper
ones, must be at least mostly transparent, otherwise, you wouldn't be able
to see through them ...

The conductive rubber fingers form a shock resitant, and generally very
reliable, I have to say, connection between the ( hard gold plated ) pads on
the PCB, and the on-glass electrodes.

On the very rare occasions that I've ever had to tamper with one of these
connections, I have cleaned only VERY gently with a cotton bud ( Q-Tip )
slightly moistened with electronics grade 99.7% isopropyl alcohol. Remember
that the electrodes on the glass are only deposited on by a chemical
process, and may not be very robust against vigourous cleaning.

Arfa

Thank you for a great explaination. [I can now see the traces on the glass
... very faint]

Any idea how to improve the "ghosting" - some of the digit segments appear
very faded when they should be fully on or fully off.

Thanks!

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"John Keiser" wrote in message
news:W7kkf.507$5V1.504@trnddc02...
Thank you for a great explaination. [I can now see the traces on the
glass .. very faint]

Any idea how to improve the "ghosting" - some of the digit segments appear
very faded when they should be fully on or fully off.

Thanks!

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Hi John

Have you considered that the problem may not be one of connection ? As these
displays generally employ matrixed drive for the segments, any problem with
the segment drive electronics, would show as bad segment contrast for the
same segment in all digits. Digit drive problems would show as all segments
being poor / missing in an individual digit.

Connection problems will show as digit-specific segment problems (
usually ).

Whilst the unit is apart, and powered, and showing its problem, you can try
applying gentle pressure along the connection edge to see if the symptoms
change. If they do, chances are it is a connection prob. If they don't, then
probably drive electronics.

Usually, the rubber connection sandwich, is reversible both ways- ie left to
right and top to bottom. Precise alignment is not usually an issue, because
of the comb pitch being much finer than the electrode pitch. You can try
reversing it either or both ways, and seeing if the symptoms change. If they
do, then the chances are that the sandwich is dirty or greasy - the chemical
structure tends to start to break down after some years, resulting in a non
conductive greasy film appearing on the surface. This is like when the
buttons on your TV remote get ' iffy '.

The sandwich is quite robust, and easily cleaned with isopropyl alcohol. If
reversing the sandwich changes the problem, or makes it worse, then the
chances are that the on glass contact fingers have been contaminated by
sandwich breakdown products. As I detailed before, you can clean the
electrodes with a cotton bud ( Q-Tip ) lightly moistened with IPA, but don't
go mad and scrub at them. A light pass, followed by letting it dry, followed
by a light polish with the dry end, will suffice.

Good Luck

Arfa