I'm still trying to repair an lcd monitor,
Can anyone tell me how lcds are typically biased.
Are they biased with AC or DC? What level is typically used?

I'm suspecting the biasing circuitry - it uses a couple of these
http://www.aimtron.com.tw/ProductFiles/AT1380A.pdf
One of them is not giving me any output.

What you really need is the service manual for your monitor, a good high
speed digital scope, a data analyser, and a good DVM just to start to get
in to it. You will also need a lot of background training in the design
philosophy of LCD monitors to have an idea of what is going on.

In the service department, we service these at the modular level only, and
use the specified test instruments to do the proper factory level
adjustments. Only simple to replace parts are changed on the boards, if
economical to do so.

LCD screens use a backplane bias, that is an AC squarewave type supply.
Depending on the design, they use a voltage range of around 3 to 5 volts.
Some designs may use more or less. The frequency, and dutycycle has to do
with the particular display design.

The pixels are matrix addressable that is working with millions of
crosspoints. The input to the screen is a multi level X - Y array of
addressing from a control buss. This must also include a Z value to
determine the amplitude of luminance. There is a groups of this for each
colour.

The actual way detailed that it works is fairly complex, and involved. For a
video display screen, there has to be a translation from a scanned position
to a pixel address location, at the same time there has to be a luminance
value that is set from a reference table.

It would be beyond the scope of emails to get in to the depth of LCD monitor
analysis, and design, to assist you in detail of how to service your monitor
at the component level.

If you give your monitor out for service, the service rep will replace the
modules one by one, until the monitor has no defects. Then he will go
through the calibration checks, and adjust as necessary, according to the
service manual for your monitor. Most of the adjustments are done with an
external interface, rather than having internal pots. Many of the newer
monitors do not even have an internal set-up menu anymore. Everything is
external.

As for computer monitor service manuals, these are not normally sold by the
manufactures. They keep their service information proprietary. They also
know that the average service shop will not have the necessary test
equipment to perform the proper service on the monitor, and most of the
parts inside are also proprietary, so there is no point in all of this.

Considering the cost of servicing any of these monitors in relation to the
purchase price of a new one, it usually does not pay to service these
monitors when they are out of warranty. The only simple service that someone
may be able to do on their own, is to change the backplane lamps, and
ballast supply. There are a fair number of electronic parts suppliers that
are selling substitute parts for this type of repair.



Some information about LCD screen operation:

http://www.freepatentsonline.com/4271410.html

http://www.planar.com/Advantages/Tec...echnology.html

http://www.eio.com/lcdglos.htm


Plasma Information, Just For Interest:
http://www.opsys.co.uk/Plasma-Physics-BASIC.html

LCD Projection Screens:
http://www.diyprojectorcompany.com/theory/lenses.htm


--

JANA
_____


"pedro" wrote in message
.. .
I'm still trying to repair an lcd monitor,
Can anyone tell me how lcds are typically biased.
Are they biased with AC or DC? What level is typically used?

I'm suspecting the biasing circuitry - it uses a couple of these
http://www.aimtron.com.tw/ProductFiles/AT1380A.pdf
One of them is not giving me any output.