> On 15/02/2012 20:22, tb wrote:
>> My 23" ViewSonic LCD (model VA2323wm) has a bright green vertical line
>> across the left side.
>> I am not much of an expert with electronics... Would this screen
>> problem be something that a person inexperienced with electronics
>> repairs could easily fix without turning to some expensive repair shop?
>> Where would I get the needed replacement parts?
>> I would hate getting rid of what is otherwise a good display...
>> PS: Item is out of warranty, so cannot go down that path!
> That could be a fault on the panel itself, which would not really be
> What I have seen happen though is that reseating the ribbon cable
> which connects the panel to the drive circuitry sometime fixes this
> sort of problem.
> If you decide to have a look, unplug it from the mains and leave
> it for a few hours before opening it, which should allow any high
> voltages to discharge.
> Then look for a (usually) flat cable which may be made of clear plastic
> with many (dozens) of very thin lines printed on it, leading from the
> panel to a circuit board.
> Look at both ends and see if they connect to sockets (many of those are
> latched by various means, some by sliding part of the socket out, some
> by lifting - I can't find a useful link though.)
> Unlatch (or slide out if not a latched connector) the cable and then
> re-attach and give it a try.
> If you decide to try this, be very careful as both printed cables and
> sockets are very, very, easily permanently damaged, and heed Paul's
> warnings about high voltages inside LCD monitors in the thread
> "CCFL or Inverter?"
I've never been able to find a good article and "take apart", that
verifies how the panel itself works.
You can find articles like this on Wikipedia. It shows the array of thin
film transistors. The transistors "charge up" or "charge down" the pixel.
And the rows and columns are swept regularly to change the level. It
is up to the capacitance of the pixel cell to not drain significantly,
in 1/60th of a second. http://en.wikipedia.org/wiki/TFT_LCD
Something drives that matrix. I managed to find one IC company page,
offering for sale row and column driver chips. What was weird about
those, is they were rated for around 50 volts or so, implying a moderate
voltage was being used for scanning purposes. If that were the case,
it helps charge up a pixel cell, in a short period of time.
Now, the next question would be, how do the (multiple) driver chips,
achieve an electrical connection to the back of the panel. Solder would
make sense, if the back of the panel was FR4 (PCB material), but I'd bet
it isn't made from a PCB. It's probably made from glass, and there could be
metal depositions on the back of the glass, to make contacts. Then, there could
be a thin rubber roll (elastomer), to make connections from the driver IC
array on a PCB, to the back of the glass.
The thing is, if you attempt to do research on the web, you'll fetch mostly
articles about small 2x16 row LCD displays, rather than panels the size
of a monitor. And the construction technique doesn't have to be the same
for those. In this example, you can see elastomer ("zebra") used between
the front and the back, but there is no guarantee an LCD monitor uses
something that flaky for large numbers of connections. http://longtech-display.com/images/lcd_type_1.jpg
In terms of panel fault types, you get the "bright pixel", which is a
single failed TFT transistor. A bright line, could be a failure of the
driver IC, or whatever is used to connect the driver IC to the panel.
When large numbers of lines fail like that, it's hard to say whether
it is just an electrical contact opening, because you'd expect them
to fail in a consistent clump. And multiple line failures seem to be
more random looking. So hard to guess what would cause that.
In any case, the level of disassembly will be "close to destructive",
in the sense that you might take the thing apart far enough for a look,
to cause permanent damage to it. So if going the disassembly route,
expect the thing to not work when it's reassembled. If any construction
material cannot withstand disassembly, the thing could be ruined.
(Elastomers can be disassembled, as long as the contact pressure
pressing down on the elastomer, is restored to the correct level.
I've taken apart things using elastomers and got them working again.
Don't get them dirty.)
For the high voltage on the inverter and backlight tubes, I just
want people to be aware there are high voltages involved there,
and it isn't a toy. The operating frequency of 25KHz or higher,
means you'd feel less of a shock if you came in contact with it
while it was running. But I'm not going to test that theory for
you :-) I've had my one "surprise" and that was enough.
At work, somebody there regularly worked with high voltage. And
when asked about shocks, his co-worker piped up "Oh, Bob [not his real
name] gets shocked all the time...", and I remember thinking
to myself "Jesus, I hope someone knows CPR".