Samsung UN65F6400 dims towards the top

[engelwood39]

I have a Samsung UN65F6400 TV. The original symptom it had was that the TV would not come on. After I removed the cable from the power board to the main board the TV backlighting came on making me think it might need main board repair. However when I hooked everything back up the TV all came back on and worked, but the TV is noticeably brighter at the bottom and gets dimmer towards the top. I'm guessing this is most likely an LED issue but this TV is going to be a bear to tear into, so I wanted to get your guy's opinion before I did this.
Side note, I did test it with a TVLED tester and it did do the same thing. It was bright towards the bottom and got dimmer towards the top.

[neilc6]

Re: Samsung UN65F6400 dims towards the top

I have found that top snap connector used in the F series could be flakey and you should check continuity from the power supply pad to the end of the connector attaching to the LEDs.

Strips should be wired in series in two sections. First section 1- to 1+ and 2- to 2+ (with 1+ connected to 2- on the power supply board) and second section 3- to 3+ and 4- to 4+. Take your LED tester and drive the strips from the back at the direct connection on the back and through the short cable and check that the LEDs light up AND the voltage is the same on all 4 pairs. This should confirm your LEDs are good without taking apart the panel and you can than focus on connectivity between the strips and power supply.

https://www.badcaps.net/forum/showthread.php?t=72299

[engelwood39]

Re: Samsung UN65F6400 dims towards the top

I have found that top snap connector used in the F series could be flakey and you should check continuity from the power supply pad to the end of the connector attaching to the LEDs.

Strips should be wired in series in two sections. First section 1- to 1+ and 2- to 2+ (with 1+ connected to 2- on the power supply board) and second section 3- to 3+ and 4- to 4+. Take your LED tester and drive the strips from the back at the direct connection on the back and through the short cable and check that the LEDs light up AND the voltage is the same on all 4 pairs. This should confirm your LEDs are good without taking apart the panel and you can than focus on connectivity between the strips and power supply.

https://www.badcaps.net/forum/showthread.php?t=72299

If I test between +1 and -1 (this is the only configuration I have yielded any LED lighting with my LED tester) I get it to light up similar to when it powers on (dimmer at the top). When I test voltage between -1 and +2 when the TV is powered up and the cable it in place I am getting in the neighborhood of 285V. When I test between -3 and +4 when the TV is on and cable is hooked up I get a reading of voltage that very quickly drops from 20V down to lower voltages and then "OL" starts over again.

One other note, when I unplug the power cable one, or maybe both of the small black relays on the left side of the board sound like they are opening and shutting.


Please let me know what you think and any other helpful tests you need me to run.

[neilc6]

Re: Samsung UN65F6400 dims towards the top

If you cant figure out how the strips are wired, you will need to take the panel off and test them from the top connections on the strips. The power to the strips should be disconnected. Are you using the LED tester with the tv power on? This could damage your tester and not how the strips are tested. You need to figure out the pairs of wires going to the strips and see if they light up and compare voltages. If all the strips are good, then you need to confirm continuity from the power supply.

[budm]

Re: Samsung UN65F6400 dims towards the top

https://www.badcaps.net/forum/attach...7&d=1555566803
You have 4 LED strings, two LED driver power supplies (one for each pair of the LED string) which are not the same as you can see the Voltage print out on the board. There are two LED driver IC's (I cannot clearly read the designators, IC9101C?, 9201C?), each IC drives two LED strings.
Remove the LED connector and test each LED string:
LED 1+ 1-
LED 2+ 2-
LED 3+ 3-
LED 4+ 4-
Report the results.
https://assets.shopjimmy.com/media/c...00627a-top.jpg
https://assets.shopjimmy.com/media/c...27a-bottom.jpg

[engelwood39]

Re: Samsung UN65F6400 dims towards the top

If you cant figure out how the strips are wired, you will need to take the panel off and test them from the top connections on the strips. The power to the strips should be disconnected. Are you using the LED tester with the tv power on? This could damage your tester and not how the strips are tested. You need to figure out the pairs of wires going to the strips and see if they light up and compare voltages. If all the strips are good, then you need to confirm continuity from the power supply.

I was not testing with the led tester when the TV was plugged in, but I was testing with a multimeter when the TV was plugged in and dimming to towards the top.

I may need to take the panel off...

[nomoresonys]

Re: Samsung UN65F6400 dims towards the top

Be VERY careful, panel is very flimsy and easy to break, suction cups are a good tool for the job.

[engelwood39]

Re: Samsung UN65F6400 dims towards the top

https://www.badcaps.net/forum/attach...7&d=1555566803
You have 4 LED strings, two LED driver power supplies (one for each pair of the LED string) which are not the same as you can see the Voltage print out on the board. There are two LED driver IC's (I cannot clearly read the designators, IC9101C?, 9201C?), each IC drives two LED strings.
Remove the LED connector and test each LED string:
LED 1+ 1-
LED 2+ 2-
LED 3+ 3-
LED 4+ 4-
Report the results.
https://assets.shopjimmy.com/media/c...00627a-top.jpg
https://assets.shopjimmy.com/media/c...27a-bottom.jpg

Hey budm,

I just want to make sure I'm understanding you right. You want me to remove the wire harness that goes from the power board to the clip that supplies the LEDs inside the TV, correct? And then you want me to test from -1 to +1 -2 to +2 and so on. When I do that I don't get any voltage on any of them. However when I do tests from -1 to +2 I get voltage that starts at around 20V and quickly counts down to 0V and resets itself to do the same cycle again instantly. This cycle happens very quickly over and over again. When using my LED driver to try to power the LED strips from that back clip I've tried them in virtually every configuration imaginable and the only way I can get them to light up is if I have them hooked to -1 and +1 only. When I do this it lights up the bottom of the TV bright and dims towards the top just like the TV lights up when it powers on by itself and everything is connected correctly.

Here are some close up pictures to show things better. One thing I tried to show in the picture is how the clip reverses the sides of that the negative and positive polarity is on where it enters the inside of the panel vs. where it comes out of the powerboard.

[engelwood39]

Re: Samsung UN65F6400 dims towards the top

Be VERY careful, panel is very flimsy and easy to break, suction cups are a good tool for the job.

that's what I was very scared of! I've done panels up to 50 in and maybe even a 55-inch and they were all very flimsy. This one terrifies me to work on where it's quite a bit bigger than that.

[budm]

Re: Samsung UN65F6400 dims towards the top

Hey budm,

I just want to make sure I'm understanding you right. You want me to remove the wire harness that goes from the power board to the clip that supplies the LEDs inside the TV, correct? And then you want me to test from -1 to +1 -2 to +2 and so on. When I do that I don't get any voltage on any of them. However when I do tests from -1 to +2 I get voltage that starts at around 20V and quickly counts down to 0V and resets itself to do the same cycle again instantly. This cycle happens very quickly over and over again. When using my LED driver to try to power the LED strips from that back clip I've tried them in virtually every configuration imaginable and the only way I can get them to light up is if I have them hooked to -1 and +1 only. When I do this it lights up the bottom of the TV bright and dims towards the top just like the TV lights up when it powers on by itself and everything is connected correctly.

Here are some close up pictures to show things better. One thing I tried to show in the picture is how the clip reverses the sides of that the negative and positive polarity is on where it enters the inside of the panel vs. where it comes out of the powerboard.

Remove the Female LED connector from the power supply board and I want you to use the LED tester to drive those 4 pairs (#1, #2, #3, and #4) of LED strings, one string at a time, then report the Voltage reading of each LED string as shown on your LED tester.

[engelwood39]

Re: Samsung UN65F6400 dims towards the top

I decided to tear it apart tonight and start checking LED strips individually. I did find that I have many many LEDs burn out and I started replacing them individually with a donor strip just to make sure it was going to work. I have one strip done now that seems to be working good.

What is everyone's recommendation as far as gluing the diffuser lenses back over the LEDs?

Thank you again for all your help!

[diif]

Re: Samsung UN65F6400 dims towards the top

What is everyone's recommendation as far as gluing the diffuser lenses back over the LEDs?

5 second fix, it's clear and UV reactive, it allows for repositioning and unlike superglue doesn't cloud the lenses and it comes in a nice applicator unlike epoxy.

[engelwood39]

Re: Samsung UN65F6400 dims towards the top

5 second fix, it's clear and UV reactive, it allows for repositioning and unlike superglue doesn't cloud the lenses and it comes in a nice applicator unlike epoxy.

Thanks! I'm going to pick some up today.

[Charleyd]

Re: Samsung UN65F6400 dims towards the top

Don't waste your time replacing individual LEDs (unless this is just to make sure that the TV is going to work as you said). More will just keep burning out. Replace the entire set with new. Shopjimmy has them in stock.