Samsung ln40b550k1f no picture but has sound

[HotHead]

Hi
I have a samsung that does power on fine, shows a perfect picture and sound. After about 2-3sec the picture goes off but the sound stays on. The picture comes back on after about 5 sec and goes out 2-3 sec later. It does this four times then the picture does not come back on and the sound is still ok.
I have tried different inputs(cable,av,ect) same results.
I haven't opened it yet.
What possibilities could it be? Most post I've read have been the inverter board, t-con, bad bulb but these post all said no picture at all.
Any insight would be a great help.

[R_J]

Re: Samsung ln40b550k1f no picture but has sound

It sounds like a problem with either the inverter or it could be a failed ccfl lamp, Check the boards for bulged capacitors, post pictures of the power supply and inverter boards. all lamps must light, of one does not for whatever reason it will shut the inverer down.

[Glitcher]

Re: Samsung ln40b550k1f no picture but has sound

Does sound like a ccfl lamp going bad. This model is also known for that problem.

[HotHead]

Re: Samsung ln40b550k1f no picture but has sound

I dont know why but i cant post pics.
I open it up and there seems to be no visible problems that i can see.
no bad caps or scorch/burn marks.
Are the ccfl s easily accessible, i would think not. Can you test a ccfl?

As for pictures, I'll try again but the page times out.

[HotHead]

Re: Samsung ln40b550k1f no picture but has sound

Here's the power supply/inverter board. this one uploaded.
It's not too clear.

[ecking767]

Re: Samsung ln40b550k1f no picture but has sound

when you say the "picture goes off", do you still see backlight coming from the screen?

try turning off the room light to confirm.

[HotHead]

Re: Samsung ln40b550k1f no picture but has sound

Goes off as in the ccfl turns off. no light whatsoever when picture is out.

[R_J]

Re: Samsung ln40b550k1f no picture but has sound

I have replaced the inverter transfomers in these before, you need to check the secondary resistance of the transformers. If my memory is correct, the three white transformers have dual secondary windings, the blue one only has one.

[HotHead]

Re: Samsung ln40b550k1f no picture but has sound

hi again, sorry for the delay. Been busy but got around to testing inverters and finally was able to upload some pics.
After reading several tutorials i decided to test the transformer on-board as a first step.
not sure if i did the test right. I tried to follow the diagrams on a few sights for primary and secondary coils but got a little confused along the way.
I have edited the photos and put in the results i got with the multimeter. I used two settings, 1: @ 200ohm and 2: @20k ohm.
Again, not sure if i did this right. Do these results make sense to any of you.

I also added two other pictures that appear to have some discoloration near some solder points of transformers. Not sure if they are burn marks or residual flux from soldering?

[HotHead]

Re: Samsung ln40b550k1f no picture but has sound

Hi again. I take it from the lack of responses I have done wrong. :-(
Sorry.
I have taken the time to remove all three white transformers from the board and have tested them.
Multimeter set to 2k ohm
Transformer #1
Primary .013 secondary #1 1.171 secondary #2 1.174
transformer #2
primary .013 secondary #1 +#2 zero
Transformer #3
primary .013 secondary #1 1.071 secondary #2 zero
Transformer 3 broke while I was removing it. I forced it. My bad.
But transformer 2 came out easily and I get no readings from either secondary.
Are the readings for transformer 1 ok?
Should I just replace all three since they are out?
Why would transformer 2 not function, is it something else that shorted it out?
Any help would be appreciated. I'm still taking baby steps here.

[budm]

Re: Samsung ln40b550k1f no picture but has sound

I would replace all 3.

[HotHead]

Re: Samsung ln40b550k1f no picture but has sound

Ok, so I am back after a long wait. Here's the update!
Ordered some transformers qgah02095 012tm32c from overseas (instead of qgah02095 ny0924db) and wasn't too sure if they were the same even though they were for the same board.
Tested the resistance of each transformer and they all appeared good. Just finished replacing all three and the tv is now working with a picture and sound for over 45 min.
Hope it last years!
Thx for the help, this site is tops!!!