Need more advice on backlight inverter

D

Dag Nygren

Guest
Hi again,

Some time ago I asked for schematics on my Samsung Syncmaster 531T
monitor as the backlight had gone out.
I have now pinpointed the fault to one side of the dual inverter.
I changed two faulty transistors that drove the output transformer.
Then the backlight worked for about 5 minutes, when it started
flickering and went off again. The worrying thing this time was that there
was a distinct smell of burned electronics around the transformer this
time....
Now the transistors are OK, but the backlight goes on for about 1 second,
then turns off, probably some protection circuitry switching off.
It seems like only the backlight of the part of the inverter that originally
was OK lights up.
One of my questions now is:
Can the CCFL tube fail in a mode that burns the output circuitry.

The inverter consists of two identical "channels" of which one seems OK, so
I can compare the readings when measuring it, but I cannot really find any
differences. I have also tried to connect the CCFL:s to the other
tubes channel and then that part turns on for the 1 second period. This
seems to indicate that the CCFL i OK ?

Any hints on where to start looking. I would buy a new AMBIT inverter, but
there seems to be no way of getting them and I am also worried about the
possibly faulty CCFL destroying the new one too.

--
Dag Nygren email: dag@newtech.fi
Oy Espoon NewTech Ab phone: +358 9 8024910
Träsktorpet 3 fax: +358 9 8024916
02360 ESBO Mobile: +358 400 426312
FINLAND
 
Dag Nygren <dag@newtech.fi> wrote:
Hi again,

Some time ago I asked for schematics on my Samsung Syncmaster 531T
monitor as the backlight had gone out.
I have now pinpointed the fault to one side of the dual inverter.
I changed two faulty transistors that drove the output transformer.
Then the backlight worked for about 5 minutes, when it started
flickering and went off again. The worrying thing this time was that there
was a distinct smell of burned electronics around the transformer this
time....
Click to expand...
I'm betting on a shorted turn /insulation failure on the transformer
secondary.

--
http://inquisitor.i.am/ | mailto:inquisitor@i.am | Ian Stirling.
---------------------------+-------------------------+--------------------------
Tad Williams has an interesting new fantasy: http://www.shadowmarch.com/
 
Ian Stirling wrote:

I'm betting on a shorted turn /insulation failure on the transformer
secondary.
Click to expand...
I tried measuring this, and comparing it with the other, but some shorted
turns cannot really be detected with a multimeter...

Sounds like a reasonable explanation, anyone knows where I can
get a CDT239b transformer ?

--
Dag Nygren email: dag@newtech.fi
Oy Espoon NewTech Ab phone: +358 9 8024910
Träsktorpet 3 fax: +358 9 8024916
02360 ESBO Mobile: +358 400 426312
FINLAND
 
Dag Nygren <dag@newtech.fi> wrote in message news:<1087293.VYGGDBjokF@newtech.fi>...
Ian Stirling wrote:


I'm betting on a shorted turn /insulation failure on the transformer
secondary.

I tried measuring this, and comparing it with the other, but some shorted
turns cannot really be detected with a multimeter...

Sounds like a reasonable explanation, anyone knows where I can
get a CDT239b transformer ?
Click to expand...
May be possible to use a generic replacement CCFL inverter and rewire
the transformer if it has the same primary/feedback layout ?

-A
 
Most likely the transformer is defective. This is common when the
transistors are defective in many of these inverters. You cannot measure
this with an ohm meter. Normally these are changed as a complete module
when defective. The lamps should be changed along with it, because
defective lamps can cause problems as well. Most service departments will
change both the lamps and inverter units together, to prevent future
problems, and to have peak performance back again.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"Dag Nygren" <dag@newtech.fi> wrote in message
news:1617185.PFbd8Yf9qj@newtech.fi...

Hi again,

Some time ago I asked for schematics on my Samsung Syncmaster 531T
monitor as the backlight had gone out.
I have now pinpointed the fault to one side of the dual inverter.
I changed two faulty transistors that drove the output transformer.
Then the backlight worked for about 5 minutes, when it started
flickering and went off again. The worrying thing this time was that there
was a distinct smell of burned electronics around the transformer this
time....
Now the transistors are OK, but the backlight goes on for about 1 second,
then turns off, probably some protection circuitry switching off.
It seems like only the backlight of the part of the inverter that originally
was OK lights up.
One of my questions now is:
Can the CCFL tube fail in a mode that burns the output circuitry.

The inverter consists of two identical "channels" of which one seems OK, so
I can compare the readings when measuring it, but I cannot really find any
differences. I have also tried to connect the CCFL:s to the other
tubes channel and then that part turns on for the 1 second period. This
seems to indicate that the CCFL i OK ?

Any hints on where to start looking. I would buy a new AMBIT inverter, but
there seems to be no way of getting them and I am also worried about the
possibly faulty CCFL destroying the new one too.

--
Dag Nygren email: dag@newtech.fi
Oy Espoon NewTech Ab phone: +358 9 8024910
Träsktorpet 3 fax: +358 9 8024916
02360 ESBO Mobile: +358 400 426312
FINLAND
 
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