Samsun UN46F6300AF No Backlight but they test good

[neilc6]

TV tries to turn on but no backlight. Power supply is BN44-00611D. Board referenced in this thread. https://www.badcaps.net/forum/showthread.php?t=56046

Unplugging cable between power supply and main board does not turn on the backlights. I pulled apart the panel and tested all the strips and they were all GOOD.

Measuring the big filter cap, I am getting 270VDC which is low since 390VDC is expected. From other thread, checked solder joints on transformers, rivets and feedback resistors and they look good.

Suspect SMPS IC ICP801 but can't read markings or find schematic. May have to order the shopjimmy repair kit. I have FAN7530 and FAN7930B chips from a previous repair but circuitry doesn't seem to match.

[R_J]

Re: Samsun UN46F6300AF No Backlight but they test good

I could be wrong but icp801 could be a SEM3050, Do you have VCC (pin8) on the ic?

[neilc6]

Re: Samsun UN46F6300AF No Backlight but they test good

Stumbled into this post which was my identical problem. He has the wrong power supply board number which is why I didn't see it.

https://www.badcaps.net/forum/showthread.php?t=66201

Measured RS802 in circuit and it was pretty high so I replaced it with a 10 ohm resistor.

Good news - power supply is working with backlights on.
Bad news- image is dark top 1/3 of the screen. Too bad I didn't see this before taking apart the panel. Pretty sure I was careful enough not to damage it. Reseated tcon connections. Think it is the backlight, will need to check the connections.

[neilc6]

Re: Samsun UN46F6300AF No Backlight but they test good

It does appear that the top strips are not getting any voltage.

Checked voltages on power supply with nothing connected CNL802. The + pins may have 0.1V but essentially 0V.

16 IF1 0V 15 IF2 0V
12 1+ 0V 11 1- 0V
10 2+ 0V 9 2- 0V
6 3+ 282V 5 3- 0V
4 4+ 0V 2 4- 0V

Diodes D9201C and D9101C tested good in circuit as well as R9113 and R9213. Used boards are around $50 so it would be preferred to repair this one.

[budm]

Re: Samsun UN46F6300AF No Backlight but they test good

Please recheck the DCV again at both ends of R9113, and R9213 against GND.
The panel has two LED strings, one looks to be open circuit.

[neilc6]

Re: Samsun UN46F6300AF No Backlight but they test good

R9213 and R9113 measure 282V DC on both ends with no load.

I checked each LED strip individually when I opened the panel. They all tested good. Wasn't sure how they were wired. There are 5 pairs of blue/black wires coming from CNL802.

With LEDs connected
IF1 0V
1+ 1V
2+ 0.4V
3+ 151V
4+ 57V

[neilc6]

Re: Samsun UN46F6300AF No Backlight but they test good

R9113 connects to 1+ pin so should get 282V on that pin. Remeasured and it is there and reheated the connector joints. Think I am losing continuity from 1+ to the LED strips since I can't measure it on the connector at the LED strips. The connectors are tricky to probe and determine the pinout since they are 2 level top snapping.

R9213 connects to 4- pin through a ferrite bead.

[neilc6]

Re: Samsun UN46F6300AF No Backlight but they test good

Fixed!

IF2, 1+ and 1- pins showed no continuity to the LED connector so I soldered them directly to the back of the main board. These connectors were still a little flakey since pushing them on the LED side can make some strips go out. Mental note to keep these cables when salvaging broken screen TVs.

Thanks again Budm for pointing me in the right direction - mainly looking for that 282V from the resistors and indicating there are wired as two sections.

[budm]

Re: Samsun UN46F6300AF No Backlight but they test good

Great, thanks for the follow-up.

[alfatv]

Re: Samsun UN46F6300AF No Backlight but they test good

I also had success with RS802, I posted my reply in original post and attached schematic that is close enough.
neilc6, thanks for pointing.

https://www.badcaps.net/forum/showthread.php?t=66201