LCD Repair

[tb]

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!

 

[Rob]

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
repairable.
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?"
HTH

 

[Paul]

That could be a fault on the panel itself, which would not really be
repairable.
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?"
HTH

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".

Paul

 

[philo]

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!

It is usually pretty difficult taking such a monitor apart
and there's a good chance you damage it.

A new monitor is all of $200 or so,
I'd probably get a new one

 

[GMAN]

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!

Unless you know how tol solder. Your out of luck. Most likely a bad capacitor
or many bad capacitors

 

[Mike S]

Trouble is with CCFL's they are as thin as a knitting needle, you only
need sneeze on them and they will crack, very, very fragile.... but this
isn't his problem though.

The only thing you can repair down to component level I'd say is the
power supply section and possibly the inverter, same with LCD TV sets,
some units have the dc to dc inverter on the power board and some
don't..... I have replaced 64pin SMD chips in TV's but these devils are
getting smaller and smaller and the pins closer and closer, a soldering
iron is really out of the question on these chips.

The way they are fitted during manufacture normally is by looking at a
TV monitor via a close up view from a TV camera.... soldering irons are
out the question here, the soldering is usually done, either wave
soldering or by hot air, this solders several pins in one attempt if not
the entire chip!

davy

Davy,

Sorry I didn't understand that I was barking up the wrong tree. Do you
have any links to the innards of a CCFL?

Mike

 

[Paul]

Davy,

Sorry I didn't understand that I was barking up the wrong tree. Do you
have any links to the innards of a CCFL?

Mike

This article is better than the one in Wikipedia. CCFLs don't have filaments
inside them. And as far as I know, the CCFL still has mercury (Hg) inside, just
a little bit. The striking voltage can be 700-1000VAC, coming from the inverter.
The tube power level in watts is around 3 watts. You only notice the power
(in the form of heat), when a panel uses a whole bunch of them (16 or more).

http://www.nelt.co.jp/english/products/ccfl/about.html

Paul

 

[Mike S]

This article is better than the one in Wikipedia. CCFLs don't have
filaments
inside them. And as far as I know, the CCFL still has mercury (Hg)
inside, just
a little bit. The striking voltage can be 700-1000VAC, coming from the
inverter.
The tube power level in watts is around 3 watts. You only notice the power
(in the form of heat), when a panel uses a whole bunch of them (16 or
more).
http://www.nelt.co.jp/english/products/ccfl/about.html
Paul

Thanks Paul.

I agree with previous posters who said to try re-seating the ribbon
cable. If the OP fixes it I hope he lets us know what the solution was.

Mike

 

[Paul]

Thanks Paul.

I agree with previous posters who said to try re-seating the ribbon
cable. If the OP fixes it I hope he lets us know what the solution was.

Mike

A single green line on the screen, is not:

1) The power supply. That would affect operation of the whole panel.

2) The ribbon cable from one assembly to another. Ribbon cables
are thin, carrying high speed serial data, in R, G, B format.
If I snip a wire, *all* the green pixels are affected etc.
High speed serial is done with differential signalling. It
would be pretty hard to single out a bright green line at
that level. If the ribbon cable fails, you'd see an image
with a very bad "tint". Or, if the sync or clock signal was
missing, perhaps the image would be scrambled in some fashion.

It could be, the point between the matrix driver chips and
the panel substrate. Or a single bad signal on a driver chip.
Or some kind of problem inside the panel (short or open on the
line). Since there could be a rubber elastomer contact between
the panel and whatever drives it, that's where I'd be looking
for a home repair. I don't know what exterior mechanical structure,
holds them together, and applies a compressive force so they stay
in electrical contact.

I've seen elastomeric contacts used on small LCD displays. I took
one apart when I was younger. There is also an elastomeric
contact in my present keyboard, so they're still being used,
and are a reasonably reliable method. To make them fail,
either takes mechanical damage that removed the compressive
forces on top of them, or chemical damage (like battery acid
attacking the metal contacts themselves). Elastomeric connections
are used when the two substrates have different temperature
coefficients of expansion, or the substrates could not take
the heat of a soldered connection (even with low temperature
solder). For glass, local heating like that might result in
lossage due to cracking of the panel. Elastomers never apply
that kind of heat stress.

It's possible the power supply *is* bad in the unit. That
happens a lot, with modern hardware. But it isn't causing that
green line at the moment. If the power supply is also bad, that
would be a double fault, where the power supply is not currently
affecting operation.

http://en.wikipedia.org/wiki/Capacitor_plague

Power is common to a multiplicity of items. When there
is a power problem, large numbers of things are affected.
Like, all of the pixels go out, at the same time, or the
board that converts the input signal into native resolution,
would stop doing its job. The effects are more global. It
is harder for a power problem, to single out one pixel or line.

Paul