Samsung UN50H5203 Blinking Standby light

[jason123]

Hi folks,
I just got this Samsung TV, and all I get out of it is 6 blinks of the red standby light. TV seems responsive to remote and button.

I started a bit backwards and went right to the LED strips. 90% dead, only 6 LEDs work. I replaced all strips with a new set. Tested with an external tester and they all light up. Put the TV back together and same thing - 6 blinks of the standby light.

I'd like to rule out the Power Supply board - there is no 'STBY' pin to main board. Can anyone suggest a way to force the backlight on, or help me troubleshoot this TV?
Thanks

[neilc6]

Unplugging the cable between main board and power supply board should cause the backlight to come on. Samsungs don't have blink codes. The blinking is the main board booting up. If the backlights come on with the cable disconnected, the main board is suspect.

Similar model here. https://www.badcaps.net/forum/showthread.php?t=70123

[jason123]

Thanks... backlight does not come on with power cable disconnected between main board and power board

[jason123]

Measurements of the LED connectors (referenced to Chassis / GND), while unit is turned on (STNDBY LED off)
Pin 1 (D+): 362.7 V
Pin 2 (D+): 362.7 V
Pin 3 (S1-): 344.1 V
Pin 4 (S2+): 344.1 V
Pin 5 (NC) : 0.01 V
Pin 6 (S2-): 353.4 V
Pin 7 (S3+): 353.4 V
Pin 8 (D-): 362.3 V
Pin 9 (D-): 362.3 V

Does this point to a bad power supply board?

[neilc6]

Last check is for the DRV_ON and PS_ON signals toggling from the main board. This will confirm a PS board fault since the backlights should come on with cable disconnected.

[yohnsee]

Sorry, wrong post

[jason123]

I don't see a DRV_ON signal. Is this the UD pin from Main?

[neilc6]

This post says UD/OD may be an error signal so the board may not have a separate BL_ON signal. I would try replacing the PS but buy from a seller that takes returns.

https://www.badcaps.net/forum/showth...7&highlight=ud

[jason123]

So it doesn't seem there is a way to force the Backlight on? The voltages on the Backlight connectors are rather high. What does that mean? these are brand new backlight strips, and I tested them individually prior to installing. Also, backlight doesn't come on with the cable between main and ps is disconnected

[neilc6]

Unplugging the cable between the PS and main is the way to test the backlights on Samsung TVs. There is no or very low voltage differential to the strips so they aren't getting any voltage. The TV going through the turn on process indicates your main board is probably ok.

[jason123]

Thanks .. i will order a new power board. It doesn't seem that it could be anything else. Thanks
I am assuming a schematic for BN44-00772a is not available and repairs are not worth it

[budm]

https://www.shopjimmy.com/samsung-bn...-led-board.htm
If you look at the Voltage chart as printed on the board, the LED Voltage with load is 235VDC, you are getting over 300V which means the LED power supply is not seeing the load. Your LED panel has 3 LED strings (S1, S2, and S3) connected in series to form one large string. I would invest in LED tester that can test each LED string.

[jason123]

Thanks budm. This TV actually has 4 LED strips. They're all replaced with a new set. I thought it was a quick Backlight replacement and I put the Panel back together before checking the connection. I have a current limited power supply that I used to test each strip separately but I don't know how these are connected to the PS board. Any idea what these D, S,... mean?

[budm]

Are not same as string, you can have 2, 3 or 4 strips connected in series to form the string, see how the traces on the bottom side of the board are done, you have 6 wires on that LED connector.
The two D+ pins are tied together and then connected to the Node of the LED string, the S1- is the Cathode of the LED string #1 which is then connected to the S2+ which is the Anode of the second string, the S2 - is the Cathode of the S2 string which is connected to S3+ which is the Anode of the 3 rd LED string, the Cathode of the third string is connected to the two D- which are tied together. You have open circuit that is why the Voltage went up over 300V. You need to verify that do have connection between the male pins of the power supply board all the way to the LED string, strips.

[jason123]

Thanks budm. That helps greatly. Applying current-limited supply of 75V to the female connector that plugs to the PS shows the strings turning on. It seems 3 strings are present (sorry about the confusion with strings / strips). one string has 15 LEDs (pin 8 and 7), another string also 15 LEDs (pin 6 and 4) and the last string is 2 strips (30 LEDs, pin 2 and 3.) Verified that the panel wiring is at least as expected as follows:

Applying Power to Pin 8 (D-) and pin 7 (S3+) turned one string on.
Applying Power to Pin 6 (S2-) and pin 4 (S2+) turned another string on
Applying Power to pin 2 (D+) and pin 3 (S1-) turned the last 2 strips (3rd string) on (I had to up the voltage to 95V since they're 30 LED total)

It seems they're connected inside the panel correctly, right? It seems the connection is coming to the female plug (that's where the voltage was applied)

Could there be another issue with the power supply to yield this result?

[budm]

Unplug the LED connector from the power supply board, leave black probe on the chassis, red probe on either one of the D+ pin of the board then turn on the TV while watching the meter to see how high the Voltage goes up to then wait 10 seconds to see how low it goes down to then turn off the TV.
Now put the red probe on either one of the D- and repeat the test, reports the results.

[jason123]

D+ went to 265 V then up to 362.6 V. It stayed there and persisted. Never dropped down

D- went to 362.1 V. It also stayed there and persisted. Never dropped down.

[budm]

That is a strange result on the Cathode return line of the LED string to have the same Voltage as the supply side that feed the Anode of the LED string.
TV unplugged TV, no LED connector in place again then check the resistance between D+ and D- pins of the board.

[jason123]

7.48 kOhm

[budm]

https://www.badcaps.net/forum/attach...1&d=1538256450
I just look at the picture, it looks like that section of LED driver gets around the diode D9XXand the ferrite beads inductor (B8xxx), please verify that the diode is OK, check it in diode mode and Ohm mode.
Also check that rectangular cap with '2j 104j' printed on top, that cap is connected between D+ and D-, you have to remove the cap and check the resistance (not ESR) to see if it has bad leakage resistance or not.
This is tough troubleshooting without the schematic, I will have to find time to trace out the circuit.