Toshiba 24sl41ou LED backlights not working

[miltown]

Hey all have this Toshiba TV. Picture is there sound is there but no backlight. I checked the voltages and at the connector to the main board the 5/12 volts are there solid at 12.02 and 5.05 volts. At the six pin connector to the LED backlights I have (from 1 to 6) 1)22.3v IRLED, 2)22.3v IRLED, 3)48.01v VLED, 4)48.01v VLED, 5)22.4v IRLED, 6)22.4v IRLED.
Not sure if the LED voltages are correct as per manufacturer. There is no labeling of what I'm suppose to have at the LED connector . On the board there is a label that says that the board should have 3 voltages 5v,12v,36v. Not very familiar with LED backlights. Also the F1 fuse on the powerboard is good.

Thanks
paul

[miltown]

Re: Toshiba 24sl41ou LED backlights not working

Anyone have a trick for testing LED array?

[miltown]

Re: Toshiba 24sl41ou LED backlights not working

http://www.technibble.com/forums/showthread.php?t=38262 Here is a link to testing LED backlights worked for me hope it works for someone else. Thanks for the help.

[budm]

Re: Toshiba 24sl41ou LED backlights not working

There should be a pin that is labeled with something like bl_ON which is the signal from the main board to tell the backlights circuit to turn on.
Pictures of the boards?

[miltown]

Re: Toshiba 24sl41ou LED backlights not working

Yeah it's all there 5v. I'm thinking something in the circuit that controls the LED lights. I guess it would be the equivalent of the Inverterboard on a CFL unit.

Thanks
paul

[budm]

Re: Toshiba 24sl41ou LED backlights not working

the power supply for the LED will be the constant current source power supply, the voltage applied to the LED strings will depend on how many LEDs are connected in series, Vf of LED is about 3.3~3.6V, so I.E. 10 LEDs string will require a little over 36VDC.
Pictures of the board?

[miltown]

Re: Toshiba 24sl41ou LED backlights not working

Ok so I will have pictures in a moment. So when bl-on is working ie....5 volts everything is good. Then when it is not working bl-on is 4.77 volts. The voltage at the LEDs from pin 1 to 6 when working are 6,23v,6.23v,36.01v,36.01v,6.23,6.23. When bl-on is low at 4.77v pins 1-6 are 22.32v,22.32v,48v,48v,22.32v,22.32v. Again backlights working is very spotty and when it does it is for a very short time. Going to take pictures now.

[miltown]

Re: Toshiba 24sl41ou LED backlights not working

Ok here are some pics :

Pic #12.20.43 is there because that is a voltage reg on the main board that has 4.77v going in and 3.27 out. Which is ok as an output as it's a AX1117 3.3 but the voltage at the connector on the main board from the power supply has 5.05 volts there. So I was thinking somewhere the voltage drops after that connector and the voltage In on the reg. seems to follow the voltage on bl-on. BTW that voltage has been as low as 4.65v at the voltage reg in and bl-on. Hope some of this helps. Thanks

[budm]

Re: Toshiba 24sl41ou LED backlights not working

"So when bl-on is working ie....5 volts everything is good. Then when it is not working bl-on is 4.77 volts." So BL-ON is still present when the backlghts go out. When TV is OFF BL_ON should be <1V, when TV is ON the BL_ON should be >2V.
You can have bad LED driver or one or two LEDs in the LED string go out which is also common problem.
For example:
https://www.badcaps.net/forum/showth...t=34566&page=6

[miltown]

Re: Toshiba 24sl41ou LED backlights not working

Thanks budm I will look into it. Thanks for the info on voltages. It's hard to repeatedly check voltages as it is very rare when the backlights come on. It's more of an opportunity when they come on and you have to be prepared as they will go back off in a minute or so.

Paul