Samsung LA22D450G1rmsg LCD TV No Backlight

[DesperateDude]

Hi Guys

I am having a strange problem with my 4 years old Samsung LA22D450G1rmsg LCD TV

The problem started 2 days ago. At first it was few times but now it happens always.

The problem is, Suddenly screen goes black and I can only hear the sound. Changed video sources and opened menu but nothing shows up.

I did the flash light test and it confirmed that black lights are off. I am saying this because with a flashlight pointing to the screen I barely see the images.

Strange thing is, this problem is random. Sometimes it fixes itself automatically after a minute or 2. Anyway at first this happened only 2 or 3 times per a day and after restarting the TV I was able to watch it but now it got worse.

Another thing is, if I keep turn off the TV for about an hour or so then it works for some time and goes black again. It has no fixed time to go black. Sometimes it starts right after turning on, sometimes after 5 minutes, 10 minutes , at first maybe after an hour.

One time when I got pictures, I did a factory reset and it went well too, but the problem isn't fixed. So this couldn't be a software problem too.

I've dissembled the TV and took some pictures of the circuit board so you guys can help me

I am confused because the problems so strange. If CCFL bulbs are burned then I couldn't get any picture at all. If Inverter board has something burned then it cannot work for a while.

I've checked the circuit board for dry joins, bulged caps and etc but found nothing.

Sorry for the long post, I had nowhere else to go but to come to you experts



Thanks

[DesperateDude]

Re: Samsung LA22D450G1rmsg LCD TV No Backlight

Please anyone?

[Andrew F. Ali]

Re: Samsung LA22D450G1rmsg LCD TV No Backlight

If it's not a 'cold solder' joint on the Inverter section and you have constant 24 Vdc supply then it's the CCFL tubes. If there is a problem with the HV Transformer the TV will shut down.

[budm]

Re: Samsung LA22D450G1rmsg LCD TV No Backlight

You may have bad solder on the wires attached to the lamps ends.

[DesperateDude]

Re: Samsung LA22D450G1rmsg LCD TV No Backlight

Thank you both of you for replying.

Can you guys tell me how to test the voltages at the bulb connectors? Because I see there is a marking saying 9000vac but I cannot figure out which points to test with the multimeter. I tried the nearest points of a single bulb connector but meter didn't read anything.

Also if one soldering point is bad per a CFL bulb then that makes both bulbs to go off ?

Can you guys also tell me other points to test with the multimeter if there are some more places to check?


Thank you..

[budm]

Re: Samsung LA22D450G1rmsg LCD TV No Backlight

You cannot test the High frequency high Voltage output with your meter unless you want to ruin your meter. The firing Voltage can be as high as 2000V and the running Voltage can be between 800~1500V. You need high Voltage probe.
The protection circuit will kick in the first 3 seconds,if the circuit detects no current flow (due to bad lamp or lamp is not connected) through the CCFL when firing Voltage is applied to the lamp, only take one bad lamp to trip the protection circuit. The circuit also detects over current.
You have four lamps in that LCD panels. The help narrowing down to find out if you have board problem or lamp/s problem is to use a pair of test lamps.
Pictures of bad lamps and bad wiring.
http://s807.photobucket.com/user/bud...?sort=3&page=1

[Andrew F. Ali]

Re: Samsung LA22D450G1rmsg LCD TV No Backlight

https://www.badcaps.net/forum/showth...er+testing+cfl
This is another budm link...this will help you also.

[DesperateDude]

Re: Samsung LA22D450G1rmsg LCD TV No Backlight

Hi Guys, Thanks for all the info.

Today I checked if there are any bad solder joints to be seen, But there were non and connectors looked fine and I am attaching pictures of them. IN these pictures I haven't much removed the rubber coating around the joints, I did that later.

By the way, when checking the CCFLs I accidentally broke one.

Anyway back to topic, I've replaced that broken one with a normal CFL bulb as budm's tutorial. Anyway with or without the CFL the problem is the same. Sometimes I see the light sometimes I don't get any.

Then the problem got worse. Now I am not getting any lights and before even without the lights I heard a hum from the transformer and now I don't hear it.

Then I checked the transformer with a multi-meter and I see open circuit for the primary winding. Before it had a meter reading now it has non. I didn't short or did anything. Just tried switching on several times with CFL and CCLFs and sometimes only with a single CFL or CCFL

I am attaching a picture of that transformer too.. It is TM-091851

Anyway I feel that Transformer was the cause for all these since the beginning. Could I be right?

Also I am thinking to buy a replacement for this transformer from eBay and at the same time buy some LED strips and replace CCFL with them (I saw some converter circuits). Is that a good idea?



Thank you..