Samsung UN55H6203AF - No Picture! - No Sound?

[TheTesterMan]

Samsung UN55H6203AF
Got this TV from a friend, about 1+ old. Was working until picture went out but still had sound. However, since I got the TV I have not been able to reproduce any sound.

Boards
BN44-00774A Power
BN57-08808A Main
?? T-con ( have not taken apart the main cover to inspect, will do this soon )

Observations
I have tried to reproduce sound by changing channels, inputs and volume.
I used a flashlight and see nothing on the screen.
It seems the TV is responding to remote Power cycle. I can see Optical Jack light up red on the Main board and a Blue LED on the T-con board.
I see no bulging caps on the Power board.
I pulled the Power board and did some preliminary shorts test, nothing found
If there is a Standby Light, or any other indicator, in front of the TV I am not seeing it ever ON

Measurements
Power Board CM863 Confirmed working ( 8 to 13V ) in response to remote
Power Board CNM803 Confirmed working Pin 6 PS_ON in response to remote
Power Board CNM804 Confirmed Pins 1, 2 ,3, 5, 7 13V

Questions
What should be the voltages on Power Board connector CNL802 ( see attached picture ). When I measure these, I measure a fluctuating voltage starting at a max and dropping to a min, then repeats ( voltage measurement dependent on using GND or Connector M?-
Is a schematic for BN44-0774A available ?
Any other suggestions on how to continue to troubleshoot this TV ?

[dick_barton]

Re: Samsung UN55H6203AF - No Picture! - No Sound?

The voltage to the leds should be 268v according to the legend on the power supply board.

[TheTesterMan]

Re: Samsung UN55H6203AF - No Picture! - No Sound?

I did not notice the 268v on the legend, thanks.. Please see below updated info/meas

Observations
I pressed the remote MENU button and then used a flashlight to look for something on the screen. This time I was able to find a menu.
I also noticed black tape on the front bezel which was covering up the Standby LED. I can now see when the TV is ON/OFF. Power cycling causes the LED to blink 5x.

Power Board Measurements
All to GND ( chassis screw )
M1+ 308vdc, M2+ 260dc, M3+ 225dc, M4+ 200dc, M5+ 0.1vdc
C9132 295vdc, CM842 242vdc, DM843C & DM842C 245vdc

Questions
Given the M1-M5 voltages, am I correct in assuming that the LED strips are in series ?
If true, then M5+ is failing at 0v, this should be reading a couple hundred volts ?
All the M measurements fluctuate starting at higher voltage, dropping for a few seconds and then flipping back to the higher voltage. This is strange for LED diodes unless caps are failing ?

[vinceroger69]

Re: Samsung UN55H6203AF - No Picture! - No Sound?

Try disconnecting the connector from the Main Bd that come from the Pwr Bd and see if the LED backlights turn on and remain on. You would see the backlights lighting from the holes at the back of the tv.

[TheTesterMan]

Re: Samsung UN55H6203AF - No Picture! - No Sound?

Vince, sorry I forgot to include this in my original observations.. yes I did try this before with same results.

[vinceroger69]

Re: Samsung UN55H6203AF - No Picture! - No Sound?

My guess probably a failed led on the strips but wait and see what others say first as theres always a risk in damaging the lcd.

these look good testers im thinking of getting one as saves stripping the lcd just to run tests
https://www.youtube.com/watch?v=4DS8_utsLPo

[dick_barton]

Re: Samsung UN55H6203AF - No Picture! - No Sound?

It does look like failed leds.

[TheTesterMan]

Re: Samsung UN55H6203AF - No Picture! - No Sound?

I agree, but before I bite the bullet and order replacements I am going to connect a power supply to each LED strip ( using connectors connecting to the Power Board ) to make sure it is one of the strips that are out. I'll continue to report my progress and hopefully subsequent fix.

[budm]

Re: Samsung UN55H6203AF - No Picture! - No Sound?

I agree, but before I bite the bullet and order replacements I am going to connect a power supply to each LED strip ( using connectors connecting to the Power Board ) to make sure it is one of the strips that are out. I'll continue to report my progress and hopefully subsequent fix.

make sure to use power supply with current limiter (limit it to about 50mA to start with) or you may damage the good LEDs.

[TheTesterMan]

Re: Samsung UN55H6203AF - No Picture! - No Sound?

I looked up the panel # and this TV uses a total of 5 rows @ 14 LEDs per, or total 70LEDs. At the Power Board rated 268v that comes to roughly 3.8v per LED which is about right. So for each row I will need at least 42v to power the strip (3v per LED x 14).
I have an adjustable power supply so setting the current limit of 50ms ( thanks budm ) and adjusting the supply voltage should be no issue. I'll report back my findings, expecting strip #5 ( M5 ) to be bad.

[TheTesterMan]

Re: Samsung UN55H6203AF - No Picture! - No Sound?

Ok, I applied 40v @ 50mA to each strip and found M4 to be defective. I now need to decide if I open it up and try to repair this strip ( I work for an LED company so I should be able to find replacement LEDs ) or simply purchase a full strip. I'll report back, I think I am going to go ahead and try the repair first.

[can]

Re: Samsung UN55H6203AF - No Picture! - No Sound?

Hello, I currently face the same issue as you. Would you mind answering some quick questions?

When you applied 40v to each Row of LEDs, which port did you use as your ground? im guessing the one corresponding to M- correct? Also, are LED expensive to replace??

[petehall347]

Re: Samsung UN55H6203AF - No Picture! - No Sound?

single led.s are cheap .new strips arent so cheap .
you may need a heat pad to change single ones as they are soldered on the back .

[TheTesterMan]

Re: Samsung UN55H6203AF - No Picture! - No Sound?

@Can.. Yes, M- is the ground.

@petehall347.. although I agree, the strips for this TV are about $20 each.. At that price I personally do not think it is worth the effort to replace the single LED.

[can]

Re: Samsung UN55H6203AF - No Picture! - No Sound?

@Can.. Yes, M- is the ground.

Got it! One more question, I just checked the voltages from M1 to M5 and its starts at around 265 M1 and drops to around 118 M5, is that usual? i know in your first post you mentioned that you observed voltages greater than those. Also these voltages do fluctuate, is that normal?

Ps. just to clarify on the issue; I can see the image of the tv (with a flashlight)

[petehall347]

Re: Samsung UN55H6203AF - No Picture! - No Sound?

@Can.. Yes, M- is the ground.

@petehall347.. although I agree, the strips for this TV are about $20 each.. At that price I personally do not think it is worth the effort to replace the single LED.

it is recommended to replace all the led.s .. well that is what i read ... i just paid equivalent amount for a second hand strip as you are quoting .
trouble is with led lamps in tv.s they are set far too high from factory and people dont know to turn them down to make them last . the last one i did had backlights set to full brightness . no wonder they only just lasted to just out of warranty .

[TheTesterMan]

Re: Samsung UN55H6203AF - No Picture! - No Sound?

@petehall347 That is interesting info, I was not aware of this, thanks

@can The total voltage for the LED daisy chain will depend on the LED and TV, so your total supply voltage may not be the same as mine. You will notice as you move through each LED strip that the voltage will drop. And yes the voltage will fluctuate slightly.

You can also check the LED strip without power and setting your meter to Diode check. A working strip will return a voltage in the forward bias while a broken strip will return nothing. Of course this will not tell you which LED is bad, but you can at least determine which strip needs replacement.

[can]

Re: Samsung UN55H6203AF - No Picture! - No Sound?

[QUOTE=@can The total voltage for the LED daisy chain will depend on the LED and TV, so your total supply voltage may not be the same as mine. You will notice as you move through each LED strip that the voltage will drop. And yes the voltage will fluctuate slightly.

You can also check the LED strip without power and setting your meter to Diode check. A working strip will return a voltage in the forward bias while a broken strip will return nothing. Of course this will not tell you which LED is bad, but you can at least determine which strip needs replacement.[/QUOTE]

I have the exact same model as you, I do see voltage on all M lines but still no backlight. The max Voltage observed is 265. Im debating weather is the power board or the LEDs, I'm leaning to LEDs but i do see voltage on all M ports.

[petehall347]

Re: Samsung UN55H6203AF - No Picture! - No Sound?

i just tested one with diode check on all led.s one by one .. the meter only has limited power but will light them up enough to see they work .. if one is very dim checking like this it might well be on its way out .

[TheTesterMan]

Re: Samsung UN55H6203AF - No Picture! - No Sound?

@can Not sure if you have a power supply available, but one way to absolutely know if the LED strips are working is to inject 40v @ 50mA and see if they light. In my case the fourth strip did not light.

I also do not think 265v is too low given that the legend calls for 268v.