Samsung UN46H5203 backlight issue - stumped

[soler88]

I am trying to fix this tv that has image and sound but no backlight. Replaced all led strips and each strip turns on using a led tester but do not get any backlight when the tv turns on.
I disconnected the main board from the PS but still no backlight.

Looking at previous threads, nothing is jumping out at me and I'm stumped.

Here are the voltage measurements:
ON STATE

CNM803 on PSU from Main

Pin 1 A13v - 13.09v

Pin 2 OD_UD - 3.3v

Pin 3 A13v - 13.09v

Pin 4 BLU_PWM - 1.6v

Pin 5 A13v - 13.09v

Pin 6 PWR_On/Off - 3.3v

Pin 7 A13v - 13.09v

Pin 8 GND - 0v

Pin 9 GND - 0v

Pin 10 GND - 0v


STANDBY STATE

CNM803 on PSU from Main

Pin 1 A13v - 13.09v

Pin 2 OD_UD - 0v

Pin 3 A13v - 12v

Pin 4 BLU_PWM - 0v

Pin 5 A13v - 12v

Pin 6 PWR_On/Off - 0.13v

Pin 7 A13v - 12v

Pin 8 GND - 0v

Pin 9 GND - 0v

Pin 10 GND - 0v


CNL802 CONNECTOR ON PSU TO LED's

ON STATE

Pin 1 D1+ - 256.9v

Pin 2 D1+ - 256.9v

Pin 3 S1- - 202.9v

Pin 4 S2+ - 202.8v

Pin 5 NC - 0v

Pin 6 S2- - 176.1v

Pin 7 S3+ - 176.1v

Pin 8 D1- - 256.4v

Pin 9 D1- - 256.4v


STANDBY STATE

Pin 1 D1+ - 207.5v

Pin 2 D1+ - 207.5v

Pin 3 S1- - 153.9v

Pin 4 S2+ - 153.9v

Pin 5 NC - 0v

Pin 6 S2- - 127.5v

Pin 7 S3+ - 127.6v

Pin 8 D1- - 207.8v

Pin 9 D1- - 207.8v


I get the following voltages with the led tester on the connector:
D+
S1- = 59.8v

S2+
S2- = 29.8v

S3+
D- = 29.8 v

Any help would be greatly appreciated. Thanks for reading!

[soler88]

Fixed!

The diode (SF28) near the the backlight connector was bad. When I measured in diode mode, it was correct 0.49v one way but not OL when reversing the probes.

Upon closer inspection, the pcb around it was darker due to heat I presume.

Hopefully this helps someone fix theirs.

[EazyBone]

Either the LEDs or PSU or connection to PSU likely. Take a good photo of power boards and then 2 additional zoomed in closer to the board.

Also disconnect the main board from PSU connector and plug in the power board. See if LEDs come on

[soler88]

EazyBone Thanks for the reply. Yes I tried disconnecting the main board from the PSU and the LEDs do not come on.

Here are some pics. Let me know if you need more zoomed in ones.

[soler88]

[Diah]

yours measurement on BL socket make no sense...
you need direct on D1- & D1+ same to S2 channel don't use the chassis as references

[lotas]

How do you measure the voltage at the output of the leds, relative to ground or something?
It is necessary to measure between D+ and D-.

[soler88]

Yes, I measured relative to chassis ground.

On those points like you indicated, I am getting 0.54v.

[Davi.p]

I think you must re check values, A13v in standby might be 8v, it confirmed , psb bad.. besides this if before power all things up the first time, you have tested B.L. with the tester the way you told my guess you have damaged the bars, D1+/- are the only pins to the leds, instead S1/3 are a series of sensors, if them are now damaged by the bad input , the driver is hang

[soler88]

Fixed!

The diode (SF28) near the the backlight connector was bad. When I measured in diode mode, it was correct 0.49v one way but not OL when reversing the probes.

Upon closer inspection, the pcb around it was darker due to heat I presume.

Hopefully this helps someone fix theirs.

[EazyBone]

Good find! I got a board in stumped on also and I can't find the culprit.. I'll recheck these myself