Prev: Philips 27PT643 (L01.1UAC chassis) constantly shorting HOT
Next: TDS544A Data Acquisition Board failure
From: dlenski on 5 Sep 2006 17:53
Andy Cuffe wrote:
> 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.

Thank you, Andy! This is exactly the info I'm looking for. On this
board, the input is most definitely around 14V. The power brick is
labeled 14V/3A as well. Perhaps the 14V is to add a couple diode drops
to the 12V?

> 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

I will look more closely for fuses. Is there any particular label used
for fuses? As in "C3"=capacitor, "R24"=resistor, "U12"=IC?

If I have to replace the inverter, is there anything wrong with using
the ones that come with the cheap case-mod kits? The backlight lamps
certainly do appear to be fried, since they have a dark gray haze
around one electrode that I don't see in any of the photos at
lcdpart.com.

Thanks a lot,
Dan

From: Bob Shuman on 5 Sep 2006 18:02
Andy's advice is right on. I'd bet that it is your inverter that went South
.... There is usually at least one surface mount fuse on the inverter board
and this can be tested with a simple ohmmeter. But, if the fuse blew, it is
usually due to a fault elsewhere on the inverter board so simply replacing
it will not likely solve your problem.

Bob

"Andy Cuffe" <acuffe(a)gmail.com> wrote in message
news:afrrf25rr8q27u2dk00lr3uemfqpv8e63o(a)4ax.com...
> On 5 Sep 2006 12:53:26 -0700, dlenski(a)gmail.com 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
>
> acuffe(a)gmail.com


From: ampdoc on 6 Sep 2006 08:55

<dlenski(a)gmail.com> wrote in message
news:1157493183.028749.246630(a)h48g2000cwc.googlegroups.com...
<snip>
>
> I will look more closely for fuses. Is there any particular label used
> for fuses? As in "C3"=capacitor, "R24"=resistor, "U12"=IC?
>

Fuses are commonly marked with F or FU.



From: jdgill on 6 Sep 2006 10:26

There are usually 4 different lines on the power connector:
1. 12 or 14 volt main power source.
2. Ground (usually 2 or more wires)
3. On/Off control line (zero or 5 volts)
4. Brightness control (zero to 5 volts).

Every inverter board I have worked on had a fuse on the main
power source. Usually located right near the input connector
and the larger electrolytic capacitor. Trace your 14 volt line.
The fuse us normally marked F1 or something like that.
They are surface mounted and may look like a black resistor.
Usually rated about 2-1/2 amps.

If the fuse is open, check the driver transistors (or FETs) that
drive the primary winding of the step-up transformers. They
usually become shorted.

Hope this helps....
John

From: dlenski on 6 Sep 2006 15:09
jdgill(a)juno.com wrote:
> There are usually 4 different lines on the power connector:
> 1. 12 or 14 volt main power source.
> 2. Ground (usually 2 or more wires)
> 3. On/Off control line (zero or 5 volts)
> 4. Brightness control (zero to 5 volts).

Thanks! As far as I can tell, all the lines on the inverter connector
are at 0 or 14 V :-(

> Every inverter board I have worked on had a fuse on the main
> power source. Usually located right near the input connector
> and the larger electrolytic capacitor. Trace your 14 volt line.
> The fuse us normally marked F1 or something like that.
> They are surface mounted and may look like a black resistor.
> Usually rated about 2-1/2 amps.

There was indeed a (tiny) fuse, I finally found it. It is not blown,
so that wasn't the problem.

After messing around with this thing some more, and accidentally
shorting 14 V to ground in the power supply, I've made the whole thing
worse. Now I can't even get an image to show up by shining a bright
light into the backlight tubes. Ugh. I think I'd better cut my losses
and stop messing with this thing. Oh well. It's been a good learning
experience!

Dan

First  |  Prev  |  Next  |  Last
Pages: 1 2 3 4
Prev: Philips 27PT643 (L01.1UAC chassis) constantly shorting HOT
Next: TDS544A Data Acquisition Board failure