SANSUI SLED6515 no backlight, has video/sound

[kuzimoto]

I recently received a Sansui SLED6515 TV from a relative for free as it's not functioning properly, and was sent a replacement from Amazon. As I'm somewhat technically inclined I thought I could attempt to repair it and have a nicer TV than what I have now.

As the title states the TV does show a picture when you hold up a light to the screen, and it does output sound. However there is no backlight at all. Also, I'm not sure if this is a result of me taking apart the TV, but after putting it back together I noticed that it makes a 2 second long buzzing sound coming from around the power supply only when turning it on. I didn't notice anything else out of the ordinary when visually inspecting components, but I'll attach photos if it can aid in further troubleshooting.

I tried to do some research on further testing but it was a bit out of my scope so hopefully someone can try to explain in different terms. I have a multi-meter for testing components but will probably need more explicit instructions.

Thanks for any assistance!

[budm]

Re: SANSUI SLED6515 no backlight, has video/sound

The power supply/LED driver board:
So what DCV do you have on CON4 BLON pin 3?
What DCV do you have on those two LED backlights connectors with red/black wires when TV is OFF? Need reading for each pin.
With the TV off, put black probe on the chassis, red probe on the red wire on one of the LED connector, then turn the TV on and watch the DCV reading to see how high it jumps up to and wait for a few second to see how much it drops down too, record those reading then do the same for the other 3 pins of the LED connectors, do not remove the connectors from the board when making the readings.
We also need good straight shot pictures of the bottom side of the power supply board.

[kuzimoto]

Re: SANSUI SLED6515 no backlight, has video/sound

The power supply/LED driver board:
So what DCV do you have on CON4 BLON pin 3?
What DCV do you have on those two LED backlights connectors with red/black wires when TV is OFF? Need reading for each pin.
With the TV off, put black probe on the chassis, red probe on the red wire on one of the LED connector, then turn the TV on and watch the DCV reading to see how high it jumps up to and wait for a few second to see how much it drops down too, record those reading then do the same for the other 3 pins of the LED connectors, do not remove the connectors from the board when making the readings.
We also need good straight shot pictures of the bottom side of the power supply board.

I hope I did this right... I have the TV plugged into power, with it OFF. The black probe is touching the metal bracket that the board sits on, and I'm touching the red probe into the tops of where the wires enter the connector touching the metal part inside. With the multimeter set to measure Voltage at 200 sensitivity none of the wires seem to have any sort of reading. None of the wires in CON4, or the pairs of wires for the two connectors to the backlight.

Here are the results of the second test, which I do the same thing on each pin, except also power the TV on:
Backlight connector 1 (closest to CON4)

   Initial  After
Red   0    0
Black  -45   0

Backlight connector 2 (farthest from CON4)

   Initial  After
Red   -47   0
Black  -119  .2

CON4 Pin 3 just stays at 4.4V

[budm]

Re: SANSUI SLED6515 no backlight, has video/sound

I need better pictures with straight shot to be able to trace out the LED connector to find out if they are connected in series or not.
So far it looks like the LED strings are connected in series.

"CON4 Pin 3 just stays at 4.4V" That is find, you do have bL-ON signal.
Try to do the same reading again but this time without the LED connectors in place.

[kuzimoto]

Re: SANSUI SLED6515 no backlight, has video/sound

I need better pictures with straight shot to be able to trace out the LED connector to find out if they are connected in series or not.
So far it looks like the LED strings are connected in series.

"CON4 Pin 3 just stays at 4.4V" That is find, you do have bL-ON signal.
Try to do the same reading again but this time without the LED connectors in place.

Attached are some more photos. There's a plastic sheet held in with pins that is difficult to remove.

After removing the two connectors and testing BLON, it still reads at 4.4V.

[budm]

Re: SANSUI SLED6515 no backlight, has video/sound

OK, so what DCV do you get without the LED connectors in place?

[kuzimoto]

Re: SANSUI SLED6515 no backlight, has video/sound

OK, so what DCV do you get without the LED connectors in place?

It's the same, 4.4V

[budm]

Re: SANSUI SLED6515 no backlight, has video/sound

I am talking about the two white connectors that connected to the 2-pin connector for the LED.
Do the same as your POST 3 but without those two connectors in place, i am trying to find out what dcv you have on those two connectors on the board without having the LED connectors in place.
You were getting 119V on one of the pin when both connectors in place.

[kuzimoto]

Re: SANSUI SLED6515 no backlight, has video/sound

I am talking about the two white connectors that connected to the 2-pin connector for the LED.
Do the same as your POST 3 but without those two connectors in place, i am trying to find out what dcv you have on those two connectors on the board without having the LED connectors in place.
You were getting 119V on one of the pin when both connectors in place.

I appears that all pins read 0V, except for the aforementioned pin which reads the same, jumps to about -116V then remains steady at 0.2V.

[budm]

Re: SANSUI SLED6515 no backlight, has video/sound

OK, I am trying to establish the LED feeding Voltage with and without the load.
One thing I like to know, if you turn on the TV in darken room and you look at the back of the LCD panel, do you see the backlights even flash on for seconds?

[kuzimoto]

Re: SANSUI SLED6515 no backlight, has video/sound

OK, I am trying to establish the LED feeding Voltage with and without the load.
One thing I like to know, if you turn on the TV in darken room if you look at the back of the LCD panel, do you see the backlights even flash on for seconds?

It doesn't look like there is any light coming from the backlights.

[budm]

Re: SANSUI SLED6515 no backlight, has video/sound

I expect the Voltage to be higher than 116~119V range for 65 inch TV and I do not know many LEDs there are inside the TV. You will need the LED tester to find out if have bad LED string or not. At this point I think the LED supply Voltage is too low, but not 100% sure.

[kuzimoto]

Re: SANSUI SLED6515 no backlight, has video/sound

I expect the Voltage to be higher than 116~119V range for 65 inch TV and I do not know many LEDs there are inside the TV. You will need the LED tester to find out if have bad LED string or not. At this point I think the LED supply Voltage is too low, but not 100% sure.

Hmm, is there any way to proceed without an LED tester? Or any way I can buy/make a LED tester on the cheap?

[kuzimoto]

Re: SANSUI SLED6515 no backlight, has video/sound

Bump, anyone have any ideas? Any help is appreciated!

[dick_barton]

Re: SANSUI SLED6515 no backlight, has video/sound

What is the maximum voltage you have on the led connectors at switch on and out of standby with / without the leds connected.
Do you have a min/max function on your meter to catch the initial dc voltage before it drops suddenly.