Samsung UN32F6300AF - No Backlight

[rm80]

Hello, I have a Samsung UN32F6300AF, I can see a picture on the screen when shining a light at it, but no backlight at all. I was wondering if someone could point me in the right direction. Does the backlight get it's power directly from the power supply? There are two cables leaving the power supply, one goes to the main board, and another appears to connect the panel. It's LED so I don't see an inverter board anywhere, just a tcon. Thanks in advance for any help.

[xgrizzlyx]

Re: Samsung UN32F6300AF - No Backlight

Hi,
I'm a new member here too.
originaly from RI
I seem to be having the same problem with my Magnavox 47mf437b37
The blue light comes on steady with no flashing or chirping.
after changing the 3 bad caps on the power board, i still get no picture.

I hope we can both benifit from the knowlege of the forum members here.

Thanks all

[budm]

Re: Samsung UN32F6300AF - No Backlight

https://www.badcaps.net/forum/showthread.php?t=39740

[rm80]

Re: Samsung UN32F6300AF - No Backlight

Sorry. Here are some pictures. https://www.dropbox.com/sh/7l4627v6v...6jiqJDhRa?dl=0

[budm]

Re: Samsung UN32F6300AF - No Backlight

Check the DC Voltage right at the two legs of the 47uf 250V cap on the top right of the power supply board (it is close to the LED strings power connector).
It looks like it has 4 LED strings in this panel.
Did you see the backlights even flash on for seconds, you may have to look at the backside of the panel or look at it in the dark room to see, that will give us a clue.

[rm80]

Re: Samsung UN32F6300AF - No Backlight

I've got 126v

[budm]

Re: Samsung UN32F6300AF - No Backlight

OK so the power supply for the LED strings is not dead. So did you ever see it flashes on once when first startup, if it did flash then we know that the circuit did try to light up the LEDs but if one of the string failed, then it goes into protection shutdown, that is the clue I am looking for.
If not, then it may not have received the backlights on signal from the main board.

[rm80]

Re: Samsung UN32F6300AF - No Backlight

It powers on immediately when plugged in, I don't have to hit the power button, I don't know if that is normal or not, but I do not see any sign of the backlight flashing or coming on for even a millisecond.

[rm80]

Re: Samsung UN32F6300AF - No Backlight

I did not try in a dark room yet, I'll try that as soon as I can.

[budm]

Re: Samsung UN32F6300AF - No Backlight

I just look at the picture of the bottom side of the board at shojimmy, check the DC voltage on the cap C9102 (22uF 250V) this cap is for the boost converter circuit that boost the 126V to higher voltage to run the LED strips.
If you look at the output voltage chart next to the two long black caps laying on their side, it has LED Driver voltage rating which I cannot due to white glue is blocking the view.
http://www.shopjimmy.com/media/catal...00606a-top.jpg

We also need to find out if the board is getting BLO signal on PIN 6 of connector CNM803 or not.

[rm80]

Re: Samsung UN32F6300AF - No Backlight

Ok, I checked in a dark room, still nothing. Under the glue it says 160v, the voltage at that cap is odd, it starts at 226v and drops to like 196v then repeats, not sure if that is normal or not. I'm not sure what I need to do to check for a signal at pin 6, do I just probe with one probe and find a ground with the other?

[budm]

Re: Samsung UN32F6300AF - No Backlight

Since the boosted voltage did go up from 126V, the LED driver power supply does get the BLO signal, you can verify pin 6 by using digital meter in DCV, Black probe on the chassis, take the reading when TV is not turned on (should be <1V) and when TV is powered on by the power switch (>2.5V).

[rm80]

Re: Samsung UN32F6300AF - No Backlight

I get no noticeable voltage when off at pin 6 and around 5v when on.

[budm]

Re: Samsung UN32F6300AF - No Backlight

"I get no noticeable voltage when off at pin 6 and around 5v when on." BLO is OK.

OK, I look at the bottom side of the board where the connector CNL802 for the LED strings are connected to, the four strings looks to be connected in series. Pin 3 (4-) and Pin 12 (1+) are the LED strings voltage feeding pins.
So at this point, I say you have open circuit in the LED string, and that is why you did not see the LEDs light up at all since all four strings are connected in series.
You can cut the wire that goes to pin 3 (4-) of CNL802 and put the meter in series with the wire to check the current draw, I built and indicator for finding out if the LED string has open circuit or not.
https://www.badcaps.net/forum/showpo...&postcount=107

[RCA2000]

Re: Samsung UN32F6300AF - No Backlight

How many lines run from the PS board--to the LED BL in the panel ? Often--there is only a pair--or maybe 2 of them I do not believe this one has a "modulated BL", meaning it dims with the video signal in different parts of the panel. If it did--there would be at least 8 wires to the BL--for different strings and a board to drive them with.

Check how much voltage you are getting to the LED BL into the panel when you power on the set. If you see say, 120-150 volts--even for a second--you likely have an open LED or more than one in the panel.

Is this a set that has a "sealed panel" and the PS and signal board mount on the bottom of the panel--IIRC_those often had a bad BL.

[rm80]

Re: Samsung UN32F6300AF - No Backlight

OK. budm, I'll try to give that a shot at some point tomorrow. RCA2000, there are 16 wires in the harness that goes from the PS to the Backlight, if that is what you are asking.

[budm]

Re: Samsung UN32F6300AF - No Backlight

This one all four strings are in series (1+/1-, 2+/2-, 3+/3-, 4+/4-) with only one Sinking MOSFET Q9102 and one Current sensing resistor R9110 (3.6 Ohms).
It has open LED circuit for sure.
The sixteen pin connector not all the pins are used: PIN 1, 2, 7, 8, 13, 14, 15, 16 are not used even though they have wires attached to them.

[rm80]

Re: Samsung UN32F6300AF - No Backlight

Ok, I haven't tried cutting the wire to check current draw yet, but you seem confident it's a bad LED strip. Do I just need to identify which one and replace it?

[budm]

Re: Samsung UN32F6300AF - No Backlight

We just found the problem in this one:
https://www.badcaps.net/forum/showth...069#post481069
So you will more likely will have to do the same thing.

[rm80]

Re: Samsung UN32F6300AF - No Backlight

It's been a while, but I got it apart and found one strip with some discoloration, I assume that is the problem one, do you know where I can find a replacement?