On 5 Sep 2006 12:53:26 -0700, wrote:

Hi all,
I am trying to repair a 19" Samsung 191T monitor that appears to have
been damaged due to a storm-related power surge over the weekend.

The problem with the monitor is clearly related to the backlight: the
four backlight lamps appear "burnt" and if I shine a bright light into
the back of the panel, the image on the screen appears perfectly fine
:-)

The monitor includes two main circuit boards: a big one that the DVI
input and power connects to, and a smaller LCD inverter board. The LCD
inverter board is an Ambit BN44-00060A, which appears nearly identical
to this one: http://www.lcdpart.com/images/AMBIT_K021036.gif
There are no fuses on either board, as far as I can tell.

The LCD inverter board is connected to the main circuit board via a
12-pin connector. The voltages output by the LCD inverter board are
very close to zero, so obviously something is wrong with it :-( If I
understand correctly, the cold cathode backlight bulbs need something
like 1000V AC, is that right?

I would like to be able to verify that nothing is wrong with the power
supply part of the MAIN circuit board as well... does anyone know what
the voltages should be on the 12 input pins to the inverter board?
Since the image is apparently fine, there is no problem with the
display electronics on the main board, but there could be a problem
with the power supply on the main board... I would like to know if
there is a way to tell this.

Can anyone give me any advice on how to test the LCD inverter and main
power supply boards? There are no fuses. Thanks for any advice!!!

Dan Lenski


The back light inverter is the most common failure on LCD monitors.
Normally you should see +9 to +12 v going to the inverter. You will
also probably see +5 and one other voltage to control brightness.

Chances are, the inverter is the problem since it usually shares its
power supplies with the LCD. Look for any fuses on the inverter
board. They will probably be small surface mount components near the
12 pin connector. That orange component to the left of the big green
capacitor could be a fuse. There may be some fuses on the bottom of
the board too. If you find any open fuses, there's a good chance that
a new fuse will fix it. About 3/4 of the inverters I see with blown
fuses have no other problems. If a new fuse doesn't fix it, you will
probably need to replace the inverter board. Schematics are rarely
available and parts are impossible to find.
Andy Cuffe