T240 Monitor Backlighting Issue

[Snev]

Re: T240 Monitor Backlighting Issue

My apologies for posting on this rather old thread.
I have the same problem as stated (multiple times) above. I've checked all capacitors. They all seem to block DC and the voltage of the electrolytic caps rises when I put the diode-tester over them. I only have a simple multimeter so I can't check other parameters. There's also no visual indication of damaged components on the board. I've also checked all the diodes.

The transformer resistances are: 905 and 921, so well within the 3% tolerance.

Does anyone have an idea?

edit: I also checked a number resistors (when possible) and of course the fuse. I've also read the 'A guide on how to troubleshoot 2 seconds to black' thread which teaches me that I probably can not do anything more with my multimeter. Still, if anyone has another idea (besides guessing and replacing all the components), it would be much appreciated.

[retiredcaps]

Re: T240 Monitor Backlighting Issue

The transformer resistances are: 905 and 921, so well within the 3% tolerance.

1) What is part number U101 (on the backside of the power board)? This has nothing to do with 2 seconds to black, but I need that information to help someone else.

2) 2 seconds to black can be (most likely)

a) bad caps
b) bad ccfls
c) bad ccfl wiring (especially the return wiring)
d) bad secondary windings on the inverter transformer

More details starting with post #19 at

https://www.badcaps.net/forum/showthread.php?t=10419

Also, see budm's Inverter tester using old CFL

https://www.badcaps.net/forum/showthread.php?t=19987

3) Your transformer readings suggest they are likely good.

4) You cannot test whether a capacitor is good or bad with a multimeter. You need an ESR meter.

5) Post clear focused top down pictures of all your boards following my sig file below exactly. We want the picture compositions like so

https://www.badcaps.net/forum/showpo...94&postcount=1

[Snev]

Re: T240 Monitor Backlighting Issue

Thanks for the information. Seems i'm quite lost without an ESR meter

U101 doesn't seem to be on the back side of the board. If you mean IC101 then i have to disappoint you by telling the part number is not readable.

[retiredcaps]

Re: T240 Monitor Backlighting Issue

If you mean IC101 then i have to disappoint you by telling the part number is not readable.

Sorry, I meant IC101.

If you have no ESR meter, concentrate on bad ccfl wiring (especially the return wiring).

[PsiQ]

Re: T240 Monitor Backlighting Issue

Hello everyone!
I found this Thread over Youtube and Google, and im also having problems with my samsung t240HD.



I shut it down and took it apart BEFORE it totally quit to function,
so i can tell, that the signal-board etc seems to be working just fine.

The Problem i had, was a slight flickering in the upper part of the screen.
When running for some time (1h), perhaps due to getting warm, the screen/picture flickered combined with a high frequency humming noise,
leading to distortion over the screen.

I'm guessing either the inverter or one of the ccfl lamps are close to dying.

As for the inverter, i measured the output pins mentioned earlier in this thread, which are both having 1,0xx.. k-Ohm resistance. (903 Ohms mentioned there)
So the inverter seems fine.
--What resistace should be on the input side of the inverter??

Due to the light flickering a bit, i guess there might be a lamp going bad.

I think the tube/lamp isnt functioning properly (flickering), leading to overpowering the inverter, which then leads to interference which influence the LCD-Picture-Data.


Any hints or suggestions?

I wanted to try to disable the Inverter/Backgrund light, to see if its only from the Backlight.

I found the "PWM brightness" Pin on the cable. To disable the lighting, do i have to set it high (3V .. 5V?) or low = 0V.
--With doing so, i could eliminate the possibility of a bad Signal Mainboard.


--As said earlier, the screen is still working, but i didnt want to wait until the existing problem and flickering kills another Component, not harmed yet.


Capacitors and PCB look all fine, no marks or bad caps visible.
Switching on and off and signal/picture are working just fine.

I dont think i would have any problems of changing the inverter, except the time for the delivery, but i also dont think its broken (yet)..

[budm]

Re: T240 Monitor Backlighting Issue

Sounds like you will need test lamp to find out what is going on or you will have to take the screen apart to inspect the lamp assemblies.
https://www.badcaps.net/forum/showthread.php?t=19987

Bad lamps:
http://s807.photobucket.com/albums/y...klight%20lamp/

[PsiQ]

Re: T240 Monitor Backlighting Issue

Okay, so i think im trying to make a visual check of the lamps.

Thank you for the reply. I've read both links.

Perhaps im lucky enough to have a bad lamp one currently blowing up,
and i can see it directly.

If anybody still needs pictures from PCB or part numbers, i can provide them since the monitor is still disassembled.

#1: get out lights
#2: check lamps
#3: get replacement... (in germany)

..Dont like the high voltage coming from the inverter..


--So i could basically use the electronics from a working (small) light bulb to test the ccfl-tubes ?


.. I think i am going to buy a new samsung 1920x1200 screen,
but it would be really great if i could reanimate the old screen. The Standalone TV-Function is kinda cool for watching tv in the background while playing. Less Power Consumption compared to my 42" Plasma.

[PsiQ]

Re: T240 Monitor Backlighting Issue

okay... found it...
used a butter knife to push out the metal knobs holding diffusor panel screen etc together,
and then when getting out the HV cables out of the holder, one already came off.

Soo. Should i try to reattach the cable by soldering it again, or do i need to replace the tube ? -does the cable come off because of the defective tube, or is the tube defective couse the cable came off??

...=> Done already!
Ok, done and found it!

When i was looking for how to get to the lights, already one of the cables came off.
So i took off the metal+plastik clips, and took out the upper two lights.

They look kinda ok, but one had a bad connection/black and oxidized.
so i cleaned the cable, cleaned the bulb, made two new shiny soldering points, soldered it together AND added an shrinkable isolating tube (?) over the formerly loosened soldering point..

Clicked all and everything together again.. aaaand.
its working. At least the light for now.

Need to recheck it, but i think somehow i damaged part of the panel in the upper right corner when closing it. Dammit. Well, still better than a 19".

=> Error was: Soldering point/connection from wire to ccfl tube. oxidized and lost contact, leading to flickering of tube , and electric discharges which distorted the whole screen/control signals.



..I only wish i knew how i cracked the screen! Dammit! I always expected the lights to break, but not the panel!

Ok, the screen is going to the trash can when the new one arrives...
The corner is cracked, not that bad, but i have one vertical and one horizontal line coming from it into the screen.
AAAND. the light is flickering in 1flicker a second, coming from the fixed tube. Gonna try reducing the brightness, see if it helps.

So no use in keeping it as a secondary screen.
Too bad, would have really liked it. So its going to be a new 24" 1920x1200, and a new 19" 1280x1024next to it.

... ok, reducing the brighness only leads to an damn humming noise. i know, thats been there from the beginning, the pwm+inverter are crap when dimming.. but brightness at 100, contrast 95 is ok, no flickerin. bit of tearing in the upper right screen.

thx.

[PsiQ]

Re: T240 Monitor Backlighting Issue

yup. took it off again. i managed to crack the upper right corner of the TN-Panels glass . Cracked: broad 3mm x 15mm length.

Guess i should be glad thats its only a quarter circle of 3cm in the upper right corner.

Now im gonna test the soldering point some time.
The Dead spot doesnt really matter for a secondary Desk-Screen or TV. Luckily the screen hast 1200 height pixels, not only 1080 height (= 1920x1200) so i can still watch full hd, when pulling it down a bit ;-).

And i have a usable screen until the new one arrives.


Nevertheless:
Thank you very much for the infos, also the infos coming from the other Forum pages, i learned a lot about the Flatscreens and the Problems appearing...

[afflux]

Re: T240 Monitor Backlighting Issue

epic.


YELLOW POINTS: 935 Ohm
RED POINTS: .594 MOhm (WOW)

So one of the transformer secondaries opened up?

I have the same symptoms as mucoast had, but

Red: ~930 Ohm
Yellow: ~1.7 kOhm

Since it's not close to mucoast's readings, but still not in the 3% tolerated diference, can I still assume the transformer is broken?


Edit: Only just realized that

Measured the resistance between the points like above:

Red: .930
Yellow: .605

Bad transformer. Plenty of information on getting a replacement in this thread.

PlainBill

Just ordered a replacement. Thanks.

[selldoor]

Re: T240 Monitor Backlighting Issue

Would have been helpful if you had referenced the picture showing the points as well.

It is sometimes worth testing off board before ordering.

Good luck with the repair - please update when complete

[afflux]

Re: T240 Monitor Backlighting Issue

Sorry, picture is the attachment in this post: https://www.badcaps.net/forum/showpo...39&postcount=4

Unfortunately, I don't have a soldering station or similar equipment, so I couldn't test the component alone. I plan to give the transformer and the board to a friend once it arrived. Should have more info in three weeks.

[g40rocket]

Re: T240 Monitor Backlighting Issue

Hi guys,

I read a lot of this thread and my Samsung T240HD has the two seconds go black sypmthoms.

Before the LCD goes faulty i noticed a burn smell when the TV was on and some flickering images.

Now everytime that i turn on the LCD, image is good but after two seconds i loose the backlight (image still runing background).

I already open the LCD but i don't see any burned inside.

I already measure the red and yellow points in the inverter transformer and i got this values:

Red = 1050 ohm
Yellow = 1050 ohm


Anyone can help me and tell me if the inverter is good or not ?

If not, what common faulty part is the next ?

Thanks in advanced.

[mariushm]

Re: T240 Monitor Backlighting Issue

Check the cable going to the light tubes.

Sometimes the wire gets loose/desoldered from the wire on the lamps and makes electric arcs and what you hear is the silicon or insulation burning up at the end of the lamps.

[g40rocket]

Re: T240 Monitor Backlighting Issue

Check the cable going to the light tubes.

Sometimes the wire gets loose/desoldered from the wire on the lamps and makes electric arcs and what you hear is the silicon or insulation burning up at the end of the lamps.

Thanks for the quick reply.

I will check that tomorrow (here it is 01 AM).

So, the inverter transformer is good right ?

[selldoor]

Re: T240 Monitor Backlighting Issue

If red and yellow points are as in post 4 then that inverter transformer looks good. Check out the wiring and report back.

[g40rocket]

Re: T240 Monitor Backlighting Issue

Hello again,

Selldor, yes my readings with the digital multimeter was done in the points that post number 4 show in the photo.


Mariushm, i check the cables and here it is my photo:





There are spares for this or should i forget this LCD ?

How this happens ?

[budm]

Re: T240 Monitor Backlighting Issue

It looks like the it has burnt wires that are attached to the ends of the lamps, one of the common failure mode.
http://s807.beta.photobucket.com/use...05283888095196

[selldoor]

Re: T240 Monitor Backlighting Issue

Hello again,

There are spares for this or should i forget this LCD ?

How this happens ?

You can get replacement tubes - needs care and patience.
You can get tubes and pre-wired kits
It may just need the wire resoldered.

see this site for info http://www.ccflwarehouse.com/lasotu.html

Also earlier in thread someone re soldered but then broke the panel glass
https://www.badcaps.net/forum/showpo...2&postcount=28

It happens because they get very very hot -the insulation breaks down
then they start arcing and the wire burns. If you repair the insulation is very important, or it will not last.

[afflux]

Re: T240 Monitor Backlighting Issue

Would have been helpful if you had referenced the picture showing the points as well.

It is sometimes worth testing off board before ordering.

Good luck with the repair - please update when complete

Was only just able to replace the transformer and test the device. Turns out the transformer was indeed faulty - now I have a working secondary screen again!

Thanks