2010 Samsung LN46C670M1F LCD - Sound but NO PICTURE

[kburks1230]

Greetings

Just got this set and she's got no picture but sound is working. Screen is completely black. I tried to shine a flashlight on the screen and I don't see anything. Completely black, no backlight at all ever. I checked Toms manual database and I unplugged CN802 but the backlight didn't come on when I plugged it back in. 2 replaceable fuses on the power board test good.

Any help troubleshooting this would be appreciated.
Thanks guys

-Ken

[tom66]

Re: 2010 Samsung LN46C670M1F LCD - Sound but NO PICTURE

Can you start by posting a picture of the TV with the back off?
Try this - in a dark room plug in the TV and turn it on. Do you see a brief flash from the backlight?

[kburks1230]

Re: 2010 Samsung LN46C670M1F LCD - Sound but NO PICTURE

Here is the back picture. I turned the lights off and tried plugging it in but I can't see the backlight come on at all, not even for a second.

[tom66]

Re: 2010 Samsung LN46C670M1F LCD - Sound but NO PICTURE

OK, the big 450V capacitors on the power supply, can you try testing the voltage across them? Be careful, it is the hot side, so there is a risk of electrocution. You need to put one probe on positive, the other on negative (only need to test one capacitor.)

[kburks1230]

Re: 2010 Samsung LN46C670M1F LCD - Sound but NO PICTURE

386v on both of them

[tom66]

Re: 2010 Samsung LN46C670M1F LCD - Sound but NO PICTURE

Good, that is OK. Can you see a part # beginning with BN44 printed on the power board? Something like: BN44-00001A

[kburks1230]

Re: 2010 Samsung LN46C670M1F LCD - Sound but NO PICTURE

Bn44-00341b

[tom66]

Re: 2010 Samsung LN46C670M1F LCD - Sound but NO PICTURE

OK. Schematic:


Is IC1801 on the top side or bottom side?

Any easy way for you to test pin 16, VDD, without removing the board?

[kburks1230]

Re: 2010 Samsung LN46C670M1F LCD - Sound but NO PICTURE

That IC is on the back. Can I flip the board and power it up while unmounted? or does it need to be grounded on the screw pads from being mounted?

[kburks1230]

Re: 2010 Samsung LN46C670M1F LCD - Sound but NO PICTURE

I took the power board out and plugged it in. I'm reading 5.25v on pin 16 of that IC.
Is pin 1 marked with a circle in the corner of the chip?

[kburks1230]

Re: 2010 Samsung LN46C670M1F LCD - Sound but NO PICTURE

Tom, any ideas?

[tom66]

Re: 2010 Samsung LN46C670M1F LCD - Sound but NO PICTURE

Yes, pin 1 is marked by the dot, then they go around anticlockwise.
So, looks like chip has Vcc.
Is fuse FS802S good?
You would need a scope to test for gate drive into transformer TI803S. This controls the inverter transistors.

[kburks1230]

Re: 2010 Samsung LN46C670M1F LCD - Sound but NO PICTURE

The fuse is good. I don't have a scope. Is there anything else I can check? Does it look like it's going to be something on the power board or could it be the inverter failure?

[budm]

Re: 2010 Samsung LN46C670M1F LCD - Sound but NO PICTURE

Check the cap CI801 (0.47uF 450V) to verify that it still show as 0.47uF.

https://www.badcaps.net/forum/showth...41B#post421250

[kburks1230]

Re: 2010 Samsung LN46C670M1F LCD - Sound but NO PICTURE

I don't have a CI801

[budm]

Re: 2010 Samsung LN46C670M1F LCD - Sound but NO PICTURE

Sorry, its CI818 next to the white ceramic fuse FS802S.
http://www.shopjimmy.com/media/catal...341b-top_3.jpg

[kburks1230]

Re: 2010 Samsung LN46C670M1F LCD - Sound but NO PICTURE

I'm reading .1nf on that cap. I took it out any put a meter on it

[tom66]

Re: 2010 Samsung LN46C670M1F LCD - Sound but NO PICTURE

Looks like it is bad then.

[kburks1230]

Re: 2010 Samsung LN46C670M1F LCD - Sound but NO PICTURE

ITS ALIVE! I replaced it with a 683k 630v from another power supply. Think it will be ok like this or do I need to order a 474k replacement?

[budm]

Re: 2010 Samsung LN46C670M1F LCD - Sound but NO PICTURE

You do need to use the correct value and type, it will affect the feedback signal and will fail if wrong type is used. It has to be for high pulse switching type.

http://www.digikey.com/product-detai...202-ND/1981474

I would go for 630V:
http://www.digikey.com/product-detai...574-ND/3088042