Samsung Syncmaster 226BW - Possible bad CCFL

[crocboy]

I have a Samsung Syncmaster 226BW LCD monitor that was working great for about a year until it gave up with the classic "2 seconds to black." I immediately opened up the monitor to inspect the power supply board. I saw no bloated caps, all diodes checked out, and the pico-fuse was at about .3 ohms. I went through most of the troubleshooting guidelines listed in the sticky, and all of the obvious tells weren't present.

After a while, I took apart the backlight to look at the CCFL tubes. I saw that one of them only lit up halfway down the tube, and it occasionally 'hisses'. The other tube lights up nice and bright.

I was thinking that maybe the bad CCFL was causing the inverter to shutdown, but it could very well be a circuitry-related problem.

Here are a couple more clues:

1. The DC output is ~2 V higher than specified (15.5 V vs. 13.5 V)
2. The main transformer makes a high pitch whining sound, except for when the lights come on, then it is silent
3. All of the main caps on the board were apparently replaced by the previous owner (You can tell from the 'human' solder joints in the pictures)


First picture: Top of the PSU board
Second pic: Bottom of PSU board
Third pic: Halfway-lit CCFL

Any help is greatly appreciated!

[Pentium4]

Re: Samsung Syncmaster 226BW - Possible bad CCFL

Who ever soldered on those caps chose good ones but did a horrible soldering job, I don't even know how they made such a mess...The CCFL's might be bad, make sure the wires have a good connection just to be sure

[smason]

Re: Samsung Syncmaster 226BW - Possible bad CCFL

Hissing could be a bad connection at the tube end. Have a close listen, and watch it in a dark room and look for arcs.
Could still be a bad tube, but worth checking.

[crocboy]

Re: Samsung Syncmaster 226BW - Possible bad CCFL

So the problem ended up being bad CCFL's - I replaced them and everything was looking good until I plugged it in - as you can see, there is a vertical row of green pixels that is always on, and there are dull, wider green vertical stripes that are easily visible when the screen is black. I haven't completely reassembled the monitor yet, so could the problem be caused by a missing metal plate and some EMI?

[Rtech]

Re: Samsung Syncmaster 226BW - Possible bad CCFL

This can occur.if you have inadvertantly damaged the screen during the CCFL change. Has happened to me a number of times,even though I have changed lots and lots of CCFLs,and take great care when doing so,for this reason.