Westinghouse DW39F1Y1 LED backlight voltage

[MagicSmoke]

Working on power supply, problem no led backlights on when powered on. Could only find one other post about this tv.

PSU has 12v stby, it will turn on and off with remote or button. LED changes from red to blue.

Voltage at led connection is 26v in stby, then at power on jumps to 85v then drops to 26v. I'm assuming the voltage is supposed to go that high as the top cap in the line of three is 100v ( it's on the led output circuit) and other 2 are 35v.

My question. Is 26v on led connector @ stby right?

Do the led strips in most tv's run that high voltage wise?

picture copied from sj.

[budm]

Re: Westinghouse DW39F1Y1 LED backlight voltage

It looks like simple boost converter circuit to drive just one string of the LED.
Did you see the LED even flash on for seconds?
You should remove the LED string connector then check each pin on that connector of the LED string ( not the connector on the PCB) against the chassis to see if it shows any resistance to Ground.

[MagicSmoke]

Re: Westinghouse DW39F1Y1 LED backlight voltage

I did not think to check for short to ground. I did check led circuit ohms and got a reading of .537 mohm on 2m scale on my meter.

Led's have not flashed even once while trying to power on. Tried the flashlight trick but could not see or hear anything.

Can the led string ohms actually be checked at the wiring connector? I just realized the .537 reading was my fingers touching the probes to the wires inserted in the led string connector.

No short to chassis though.

[budm]

Re: Westinghouse DW39F1Y1 LED backlight voltage

We are looking to see if the wires to the LED assembly inside the panel may be shorted out to the chassis or not, but you have to remove the female connector from the board first and use small resistor leg to make contact with female terminals inside the connector to check the resistance against the chassis.
You cannot test the LED string to see if it has open circuit because the meter does not put out enough Voltage to turn on the LED.
You may have one or two LEDs that had gone open circuit which is a common failure.

[MagicSmoke]

Re: Westinghouse DW39F1Y1 LED backlight voltage

Not shorted to chassis, but I did take it apart to check led strips and found one strip with 3 brown tinted led's on it. There are heat marks on backside of strip. One shows open the other 2 shorted.

Thanks for pointing me in the right direction.

[budm]

Re: Westinghouse DW39F1Y1 LED backlight voltage

That is so sad that they move away from CCFL which requires high Voltage and creates lots of heat and uses lots of power and move to using LED which does not require high Voltage to run and yet they still cannot make it last.
You can use this method to find out if the LED string has open circuit (no current draw):
https://www.badcaps.net/forum/showpo...4&postcount=95
Or this way:
https://www.badcaps.net/forum/showpo...&postcount=107