"Michael Kennedy" wrote in message
...
I have a NEC Multisync LCD 1525M Monitor with a bad inverter (built by
Potrans model# DA00812600). It had a burnt 22 pF 3kv ceramic capacitor. It
is the cap just before wher the ccfl lamp hooks up. I replaced this cap
with the closest value I could find at the local surplus dealer, a 24pF 1kv
cap. I also replaced the .5a fuse with a regular fast blow and tried it
out. It worked for a short while. I powered it off and back on and it blew
the .5a fuse. I don't know if the original was a slow blow or not, but I
can't get anything out the side that had the burnt cap.

I can't find any shorts on the board and don't really know where to go
from here.. Any poiters before I replace every component on the board?

Here are some pictures.. I know the fuse i put on there looks really bad
but I didn't have a small resistor sized fuse to go on there.
Before
http://mikescomputers.homeip.net/LCD/DSC00357.JPG
http://mikescomputers.homeip.net/LCD/DSC00358.JPG
After
http://mikescomputers.homeip.net/LCD/DSC00365.JPG
Whole board
http://mikescomputers.homeip.net/LCD/DSC00361.JPG


The original was probably a slow blow at probably 1 or 1.25 amp (but I'm
guessing). The ccfl's are probably 4 watt bulbs, 2 of them, total draw 8
watts, inverter efficiency is around 75% which means the whole thing is
drawing 10 watts when running correctly. With a 12 volt supply and you get
just under an amp draw.

If you have a scope, see what kind of a trace you get on either side of C9.
If the transformer is open on the secondary, you'll get a clean 1/2 wave on
either side of C9. If it's working, you'll get the 1/2 wave but it will be
misshapen and may have some harmonics on it. The voltage on C9 side is low
since you are on the primary. The inverter will usually work for about 2 -
4 seconds with the bulbs unplugged. The square chip in the center is the
controller and will shut the inverter down if it doesn't sense the bulbs
light up. Here's a file that should give you a close approximation of your
inverter: go to http://www.anachip.com/eng/supports/tech/appnote.php and
take a look at ANP005

The other thing you can do is to check continuity on the transformer. The
primary windings and the feedback winding are very low but the secondary
winding should be 100 to 400 ohms if I recall correctly.

That charred board may end up being your biggest liability since the voltage
on that side of things normally runs around 600vac @ 60Khz or so. It might
just be easier to find a cheap monitor with a cracked LCD on eBay and take
the boards out of it.

Dave