I beleive I have found a shorted zener diode at ZD1 it ohms 119 both ways.
ZD2 on the opposite side of the board ohms 343 foward and over 700 reverse.
I guess that is why I'm blowing fuses. Now to get a chart on how to read
zener diodes.

- Mike

"Dave" wrote in message ...
"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