Samsung UN46H5203 with backlight issue

[frannyjunk]

So I got a free Samsung TV that turns on and I can see something on the screen with a flashlight (screen is very dark otherwise). I measured the power supply board output to the backlights and got the following:
(on/off)
1 D+ (181V/205V)
2 D+ (181V/205V)
3 S1- (169V/193V)
4 S2+ (169V/192V)
5 NC (0/0)
6 S2- (147V/170V)
7 S3+ (147V/170V)
8 D- (0/0)
9 D- (0/0)

Are the LEDs OK? Is power supply board OK? Do I need to check output to mainboard?

Any help is much appreciated. Thanks.

[R_J]

Re: Samsung UN46H5203 with backlight issue

It s likely you have an open led in the string, There is likely one or more led's open in the string that is connected between S3+ and D-. Or there is a bad connection in the panel string.

[frannyjunk]

Re: Samsung UN46H5203 with backlight issue

It s likely you have an open led in the string, There is likely one or more led's open in the string that is connected between S3+ and D-. Or there is a bad connection in the panel string.

Thanks RJ! Just so I can learn, how can you tell that there might be open LEDs between S3+ and D-?

[R_J]

Re: Samsung UN46H5203 with backlight issue

Thanks RJ! Just so I can learn, how can you tell that there might be open LEDs between S3+ and D-?

The leds are ALL in series, when you masured the voltage (which is high) there was close to the same voltage at all the points you checked, NO current flow results in NO voltage drop along the string.
These voltages are approximations, but if the backlights were working, D+ would be about 135v; S1-/S2+ around 100v; S2-/S3+ around 70v and D- around 20v

[frannyjunk]

Re: Samsung UN46H5203 with backlight issue

The leds are ALL in series, when you masured the voltage (which is high) there was close to the same voltage at all the points you checked, NO current flow results in NO voltage drop along the string.
These voltages are approximations, but if the backlights were working, D+ would be about 135v; S1-/S2+ around 100v; S2-/S3+ around 70v and D- around 20v

Very good to know. Thanks!!! Now all I have to do is not break the LCD panel when I change out the LED strips.

[R_J]

Re: Samsung UN46H5203 with backlight issue

Very good to know. Thanks!!! Now all I have to do is not break the LCD panel when I change out the LED strips.

Yes be very careful, Also once you have installed the led strips, test the tv without the panel installed to make sure the led's are working correctly, that way you only reinstall the lcd once. and be sure it is seated properly before installing the front bezel etc.

[frannyjunk]

Re: Samsung UN46H5203 with backlight issue

Will do. Great tip. Thanks RJ!