UN49KU7000, has sound but no picture

[hamlin86]

Hello,

I want to apologize for the very vague synopsis of my issue. I do not have the tools to test voltages either...

I got this tv about a year ago. About 3 weeks ago while watching Netflix a random black line showed up vertically. It wasn't solid so I continued using the tv and just dealt with it. 1 week later it was gone and all is good...until last night. I turn on the tv and now I have no picture at all! I can hear sounds from the menu but no picture. I did the “flashlight test” and I can see a faint image of the menu in the dark when I shine a flashlight on the TV.

I took off the back of the TV and there are only 2 boards. A yellow power supply/LED board and the main board. I looked at the capacitors and none of them looked like they went bad. I unfortunately do not have the tools to test voltages but any advice would be helpful. The main board and power board would cost me roughly $30-$40 each so I am not too concerned about having to purchase one or both of them.

Thank you.

[Andrew F. Ali]

Re: UN49KU7000, has sound but no picture

If you disconnect the connector on the PSU that goes to the Main Bd. Do your Backlights come ON and stay ON??

[nomoresonys]

Re: UN49KU7000, has sound but no picture

Grab a cheap digital multimeter less than 20 bucks, do some basic tests, video how to in my signature below.

[hamlin86]

Re: UN49KU7000, has sound but no picture

If you disconnect the connector on the PSU that goes to the Main Bd. Do your Backlights come ON and stay ON??

When I get home from work today I will try it out.

If the backlights stay on I assume it's the mainboard? What if they don't come on? Does that mean it could be the power supply board?

[hamlin86]

Re: UN49KU7000, has sound but no picture

If you disconnect the connector on the PSU that goes to the Main Bd. Do your Backlights come ON and stay ON??

I tried it and the tv doesn't turn on at all if I do that

[Diah]

Re: UN49KU7000, has sound but no picture

try to find some one help you with knowledge to repair your TV backlight... its LED backlight issue need to take the panel apart.. check here many maybe be have shop near to yours home

[jjanssen7]

Re: UN49KU7000, has sound but no picture

Take a picture of the powersupply caps (the ones closest to the connector that goes to the backlights) and upload it here so we can take a look. Certain versions of the powersupplies in these tvs have under-rated caps or a bad batch. You'll see the tops are crowned. I've worked on 3 or 4 of this particular model that need them replaced.

It may not be your issue, however, because typically it presents as flicker which gets worse until the backlights don't work at all.

[Andrew F. Ali]

Re: UN49KU7000, has sound but no picture

This is a failed Backlight issue. If you want to fix it then you would have to pull the Panel apart.

[hamlin86]

Re: UN49KU7000, has sound but no picture

Take a picture of the powersupply caps (the ones closest to the connector that goes to the backlights) and upload it here so we can take a look. Certain versions of the powersupplies in these tvs have under-rated caps or a bad batch. You'll see the tops are crowned. I've worked on 3 or 4 of this particular model that need them replaced.

It may not be your issue, however, because typically it presents as flicker which gets worse until the backlights don't work at all.

Here is the uploaded pictures

[budm]

Re: UN49KU7000, has sound but no picture

Power supply/LED driver board BN44-00876A
https://www.shopjimmy.com/samsung-bn...-led-board.htm

LED connectors CNL802 pins are labeled so you can take the DC V reading of each pin with ref. to chassis GND by leaving the black probe on the chassis, red probe on LED connector pin 1 (1+) which is labeled with black triangle mark next to the pin, the turn the TV and see how high the Voltage jumps up to, You need to set the meter to be able to read over 200V range.

[hamlin86]

Re: UN49KU7000, has sound but no picture

Power supply/LED driver board BN44-00876A
https://www.shopjimmy.com/samsung-bn...-led-board.htm

LED connectors CNL802 pins are labeled so you can take the DC V reading of each pin with ref. to chassis GND by leaving the black probe on the chassis, red probe on LED connector pin 1 (1+) which is labeled with black triangle mark next to the pin, the turn the TV and see how high the Voltage jumps up to, You need to set the meter to be able to read over 200V range.

Okay I'll go get a multimeter today after work.

Quick question...

In my 3rd picture (the picture of both boards) there are 2 ribbon cables connected to the mainboard and they are going into something. What do those do?

[nomoresonys]

Re: UN49KU7000, has sound but no picture

They are going to your t-con, tcon may be built in on this model and not removable/replaceable, can't tell exactly from the pic.

[hamlin86]

Re: UN49KU7000, has sound but no picture

They are going to your t-con, tcon may be built in on this model and not removable/replaceable, can't tell exactly from the pic.

Ah okay. Hopefully those aren't the issue....

[spotty123]

Re: UN49KU7000, has sound but no picture

Get the led tester from Shop Jimmy a great tool

[hamlin86]

Re: UN49KU7000, has sound but no picture

Power supply/LED driver board BN44-00876A
https://www.shopjimmy.com/samsung-bn...-led-board.htm

LED connectors CNL802 pins are labeled so you can take the DC V reading of each pin with ref. to chassis GND by leaving the black probe on the chassis, red probe on LED connector pin 1 (1+) which is labeled with black triangle mark next to the pin, the turn the TV and see how high the Voltage jumps up to, You need to set the meter to be able to read over 200V range.

Okay I tried that and got 361 dc voltage and 630 ac voltage. Is that good?

[budm]

Re: UN49KU7000, has sound but no picture

Okay I tried that and got 361 dc voltage and 630 ac voltage. Is that good?

If you are 100% sure the meter shows 361VDC then you have open circuit some where in the LED string, the LED drive Voltage is printed on the board, it is rate at about 200 VDC.
Try measuring the 1- and 2- pin to see what you get.

[hamlin86]

Re: UN49KU7000, has sound but no picture

If you are 100% sure the meter shows 361VDC then you have open circuit some where in the LED string, the LED drive Voltage is printed on the board, it is rate at about 200 VDC.
Try measuring the 1- and 2- pin to see what you get.

I’ve attached pictures. The dc363 is on the one with the triangle (+1). The 291 dc rating is on the -1. I am unsure of where the -2 is. Hopefully my pictures can help you identify if I am doing anything wrong. Also this is the voltages with the tv on.

[budm]

Re: UN49KU7000, has sound but no picture

The exposed pins that you can see from the top side of the board are for the Odd number pin. The Even number pin you will have probe from bottom side of the board or the wires entrance side of the connector.
The two LED strings are connected in series to form one large string, you can look at the bottom side of the board to understand how the LED strings are wired up at the LED connector.
Per connector pin chart as printed on the board
LED string IF1 (LED string # 1)
Pin 2 = 2 + (Not used) This pin is connected to pin 4
Pin 4 = 2 + (Anode of the LED string)
Pin 6 = Not used
Pin 8 = 2 - (Cathode of the LED string) This is the return line for the LED string.
Pin 10 = 2 - ( Not used, it is connected to pin 8)
Pin 12 = Not used

LED string IF2 (LED string #2)
Pin 1 = 1 + (Not used, it is connected to pin 3)
Pin 3 = 1+ (Anode of the LED string) The Boosted LED drive Voltage is fed to this pin
Pin 5 = Not used
Pin 7 = 1 - (Cathode of the LED string) This pin is connected to Pin 2 (2 +)
Pin 9 = 1 - (Not used, it is connected to pin 7)
pin 11 = Not used.
So you have 4 pins total that you need to test, but based on your reading of pin 1 it indicates that the power LED power supply is not seeing the load so that is why the Voltage on pin 1 went over 300V, but we still need to see the readings of all 4 pins.

[hamlin86]

Re: UN49KU7000, has sound but no picture

The exposed pins that you can see from the top side of the board are for the Odd number pin. The Even number pin you will have probe from bottom side of the board or the wires entrance side of the connector.
The two LED strings are connected in series to form one large string, you can look at the bottom side of the board to understand how the LED strings are wired up at the LED connector.
Per connector pin chart as printed on the board
LED string IF1 (LED string # 1)
Pin 2 = 2 + (Not used) This pin is connected to pin 4
Pin 4 = 2 + (Anode of the LED string)
Pin 6 = Not used
Pin 8 = 2 - (Cathode of the LED string) This is the return line for the LED string.
Pin 10 = 2 - ( Not used, it is connected to pin 8)
Pin 12 = Not used

LED string IF2 (LED string #2)
Pin 1 = 1 + (Not used, it is connected to pin 3)
Pin 3 = 1+ (Anode of the LED string) The Boosted LED drive Voltage is fed to this pin
Pin 5 = Not used
Pin 7 = 1 - (Cathode of the LED string) This pin is connected to Pin 2 (2 +)
Pin 9 = 1 - (Not used, it is connected to pin 7)
pin 11 = Not used.
So you have 4 pins total that you need to test, but based on your reading of pin 1 it indicates that the power LED power supply is not seeing the load so that is why the Voltage on pin 1 went over 300V, but we still need to see the readings of all 4 pins.

Okay I tested every pin. Only 2 them gave me readings. It's the first two on the top so it would be pins 2 and 4 or it's pins 1 and 3. No other pins have voltage.

[budm]

Re: UN49KU7000, has sound but no picture

You need to test with LED (Load) in place, exposed pins on top side of the board are ODD number pins, not even number pins.