Samsung LE40r87BD, backlight working but no picture

[trunkmonkey]

Hi!

I'm trying to repair a Samsung LCD-TV LE40R87BD and have run out of skill. The backlight and sound is working which leads me to believe it's either the t-con board or the lcd panel. When i power on the tv the little red led blinks for a few seconds before the set comes on but i don't know if that's normal since i haven't seen the tv in working order.

The IC located just up and to the left of the sticker on the t-con board looked a little burnt on the backside of the card, but i don't know how to check if its damaged. I have also checked the fuse (FP1) on the t-con and it's working.

I have tried to unplug the ribbon cables one at a time and both but the display did not change. Isn't the screen supposed to go white when the t-con is disconnected? Is there a way to check if the lcd-panel i defective?

Any help will be greatly appreciated!

trunkmonkey

[tom66]

Re: Samsung LE40r87BD, backlight working but no picture

What voltage do you see on each end of fuse FP1?

[truep]

Re: Samsung LE40r87BD, backlight working but no picture

The red light blinking is the normal startup.

[trunkmonkey]

Re: Samsung LE40r87BD, backlight working but no picture

Voltage on FP1 is 13,7V both ends

[tom66]

Re: Samsung LE40r87BD, backlight working but no picture

OK, on the bottom left of the t-con board, there is a bunch of capacitors labelled CD04, CD06, CD05... etc

Do you see these?

Can you test the voltage across them?

[trunkmonkey]

Re: Samsung LE40r87BD, backlight working but no picture

CD01-08 all have 13,7V on the upper side, 0V at the bottom.

CD33-35 have 3,35V at top, 0V at bottom.

Thanks for the quick replies!

[tom66]

Re: Samsung LE40r87BD, backlight working but no picture

OK, that is not right at all, there should be around 15V there. The low voltage there will cause VGGON and VGGOFF to go missing too, they are generated off the 15V usually. I would suggest a defective t-con board is at fault here.

[trunkmonkey]

Re: Samsung LE40r87BD, backlight working but no picture

Ok, I feel more confident ordering a new t-con board now since it's not behaving properly.

Thanks a lot for your help!

trunkmonkey

[trunkmonkey]

Re: Samsung LE40r87BD, backlight working but no picture

I finally got around to replacing the t-con board but it made no difference, same symptoms as before. Any other ideas on what might be the problem?

[tom66]

Re: Samsung LE40r87BD, backlight working but no picture

Can you repeat the tests I outlined above?

[trunkmonkey]

Re: Samsung LE40r87BD, backlight working but no picture

I checked the capacitors CD04-08 and now they have 15V.

By the way, where do you find info on this kind of stuff?

[tom66]

Re: Samsung LE40r87BD, backlight working but no picture

Experience.

Well, your old T-con was bad, and your new T-con is now working... so, I can only suspect that either the main board or panel is bad unless you have got a partially functional T-con.

Can you try unplugging one side of the LCD panel ribbons, there are two one for left half and one for right half.

[trunkmonkey]

Re: Samsung LE40r87BD, backlight working but no picture

I unplugged the left one and the left side of the screen went white and vice versa.
I guess this means something went wrong with the main board and killed the t-con in the process?