> OK, so some people around here work with LCDs...
>
> We've got a laptop at work with a cracked screen. Around where the crack
> is, the pixels are all black. Which isn't surprising. Slightly more
> interesting is the red vertical lines that seem to extend vertically
> outwards from the cracks. Why red? Why every other pixel? Why vertical?
> I have no idea.

It's more than likely due to the column drivers malfunctioning. One 
possible column driver scheme is to use only one DAC for each *pixel* 
column (not sub-pixel) and then multiplex the output between RGB 
subpixels. It saves by a factor of 3 the number of DACs needed and the 
number of wires to/on the panel. What is likely happening is that when 
each row is getting refreshed, the driver is reset as data is clocked 
in, red is likely first and it gets screwed (because all the column 
tracks are broken at the crack so the wrong capacitance and resistance 
or possibly even shorted) and it never manages to switch the output to 
the green and blue columns.

Another possibility, if the drivers are on the glass substrate itself, 
or a bare IC bonded to the glass, is that they got damaged when the 
crack was made.

> What's weirder still is that close to the cracks, the dead pixels
> exhibit a curiously fractal pattern. It looks like some kind of weird
> pixellated plant growth or something. Does anybody have any idea why?

The "growth" bit is because gradually moisture is getting in to the LC 
material through the crack. They are normally completed sealed in, I'm 
not a chemist but I know moisture+LC is bad and gives those patterns 
even without a crack. Also does the pattern move when you press around 
the crack? It's likely the cell-gap (distance between the inner two 
faces of glass) has changed due to the crack, that normally needs to be 
very accurately controlled to create a uniform image.

Post a reply to this message