How to fix the LCD

2002-03-15 News Flash!

Something that all owners of the CX Series II will experience is that the LCD
looses a segment or two. As you probably already discovered you can get the
segment to reappear by gently pressing the display element. Don’t do that!
It may put even more stress on the tiny plastic towers thru which the back cover
is screwed.

However, it’s easy to fix the display as long as all of the plastic covers are intact.
I’ve seen horrible methods on several other units. The unit on these pictures
had two long screws drilled thru everything...

But first, here’s some general information about LCD, Liquid Crystal Display.
As the name hints there’s a liquid contaning crystals incorporated. The liquid
is trapped between two layers of glass. One of the layers has an electric
leading pattern etched upon its surface. The other one has a thin “ground” layer.

When inactive the crystals are oriented in a random way. Ordinary sunlight
would go thru with the exception of a damping factor (some of the photons
are of course reflected but most of them will go thru).

If a current is lead thru the crystal liquid, all of crystals will point in the same
direction. I.e. it will locally act as a Polaroid filter. This feature will not by itself
stop or let thru any light.

But if the light thru the LCD is polarised (only photons in one single direction
will reach the LCD from behind) the liquid will act transparent (or blocking)
when activated. Which of the two effects is determined by the way the Polaroid
filter is oriented.

It is possible to reverse the characteristic of any LCD by turning the polarisation
filter. On the CX LCD this filter however is glued to the front glass.

One major drawback is that the liquid will be sluggish when it is cold.
Wintertime this is why the display almost doesn’t work during the first 5-10 minutes...

So, lets get down to business:

Mark each LCD with a fine point whiteboard (easy wipe!) pen directly on
the front. This way you know which LCD goes where and what is up and down.

Unscrew the complete display unit by the two screws, one on each side.
Carefully disconnect the connector.
Go inside and use a well-lit table!
Unscrew the back cover. Turn the unit so that you have the front
towards you.
Carefully remove the front cover. You can help the LCD's to stay in
place with a finger.
If any LCD unit comes apart with all the filter layers higgledy-piggledy,
don’t worry! I’ll tell you later in which order to mount it...
Lift the clamp on the left side and slide the cover out.
(not necessary...)
Now you can lift the whole circuit board out. Or let it stay and use the back
cover as a working support.
You may have two or three LCD’s depending on model. The one in the
picture is the version with trip computer. The fix is the same regardless...
The main reason for the missing segments is that the connection between
the PCB (Printed Circuit Board) and the LCD has oxidised connector pads
on the PCB

has dirt on the LCD glass connector pads
is in lack of sufficient pressure keeping the LCD in place

The connector between the PCB and the LCD is made of coal and rubber.
The screws holding the complete display unit together are the only force
clamping the LCD to the PCB. I’ll leave it up to everyone in what way you
find it acceptable to screw the back cover firmly enough. As you can see this
one needs new screw hole. Maybe I’ll glue a nut on place...
Be-all and end-all, you must clean the connecting pads on the PCB,
carefully use dry steel wool.
Then use an ear cleaner and clean all connecting surfaces with isopropyl
alcohol. Bare in mind that the etched connecting pads on the LCD does
NOT withstand any physical violence.

(Why isopropyl alcohol? This alcohol doesn’t dry out rubber. It is fairly
non-aggressive to surface treatments and plastic covers on your stereo.
It is useful to clean your tape recorder pressure roll or the VCR-head.
You can buy the horrible expensive 20 ml bottles sold at your local home
stereo dealer or as at least here in Sweden per litre from the pharmacy)

The adhesiveness of the rubber connectors should be strong enough to just
be pressed in place on the LCD. This will never happen if any dirt or grease
is left. Of course the white plastic frame will hold the rubber connector in
place anyway so...

Take the opportunity to clean the three plastic films colouring and diffusing
the back lighter bulb.
Mount in the following order:

On the PCB, put the white plastic holder in place.
With a pair of tweezers, carefully put the two rubber connectors in place.
Do NOT touch the connector with your greasy fingers!
Diffusing film, it is white and has one dull side. The dull side goes towards the bulb.
Green colour film
Silver reflex film. The silver gleaming side goes towards the LCD. This is to
enhance the contrast from light falling into the digits from the coupe side.
Finally put the LCD in place. Make sure that you've turned
it the right way...
Just to be sure you can connect and test the unit before you
mount it properly. Also, be sure not to drop the damned thing
in the car with everything lying loose...

Screw it all back together. Keep in mind that the main reason for the
dropouts was dirt/oxide. You don't have to press the unit harder than
the original screws admit. Also, the white plastic holder protects the
rubber connectors from being squeezed to hard anyway.

Good luck!

NewsFlash!

2002-03-15

I just figured out that it is easier to mount the everything towards the front
instead of towards the PCB.

I.e.;

first put the LCD in the front
then the silver film
then the green film
then the diffusor film
then the white plastic holder
and finally put the two rubber connectors in place

It was possible, I noticed, to see the pattern of the LCD in reflected sunlight.
So you can figure the right orientation out!