Toshiba 32W1343DG No Backlights, Flashlight Test OK, TV is already broken

[ReeceyBurger123]

Re: Toshiba 32W1343DG No Backlights, Flashlight Test OK, TV is already broken

Hello, good news. The repair was successful with the stacking method.

The TV works wonderful. The illumination is very even, there are no spots although there are LEDs of a different model. Color temperature and luminosity are identical

Thanks again for your help, especially on ReeceyBurger123

Awesome work enjoy the Tv hopefully lasts a few more months now lol

[budm]

Re: Toshiba 32W1343DG No Backlights, Flashlight Test OK, TV is already broken

Good job and make sure to turn down the backlights level to as low as possible to extend the life of the LEDs.

[eltrash]

Re: Toshiba 32W1343DG No Backlights, Flashlight Test OK, TV is already broken

Yo, thank you for this hint.

@ReeceyBurger123: Is your Techwood TV from stacking video still working?

[ReeceyBurger123]

Re: Toshiba 32W1343DG No Backlights, Flashlight Test OK, TV is already broken

Yes every led backlight I have fixed is still working. Some sold way over a year..

[Maxmad]

Re: Toshiba 32W1343DG No Backlights, Flashlight Test OK, TV is already broken

why the leds drain so much current, about 300mA at the start of the TV?
After few seconds the current drain drops to about 30-40mA.

[ReeceyBurger123]

Re: Toshiba 32W1343DG No Backlights, Flashlight Test OK, TV is already broken

Thats how the Pwm circuit works, higher current lower voltage then higher voltage lower current to help adjust the brightness. At start they are at brightest then they dim basically.

[Maxmad]

Re: Toshiba 32W1343DG No Backlights, Flashlight Test OK, TV is already broken

I replaced a dead led with a 5050 SMD (think 0.5w from a led strip) and only lasts about 3 minutes!
What kind of led uses? Are they so powerful??

[ReeceyBurger123]

Re: Toshiba 32W1343DG No Backlights, Flashlight Test OK, TV is already broken

1w 400ma type, or use a sub for it like a diode or resistor.

[Maxmad]

Re: Toshiba 32W1343DG No Backlights, Flashlight Test OK, TV is already broken

hard to find them as single leds without strip glass...
probably i will use the 5050 with a parallel resistor...

[Maxmad]

Re: Toshiba 32W1343DG No Backlights, Flashlight Test OK, TV is already broken

still how this think works confuses me...
I used only a 82 ohm resistor 1 watt and it burned at once!
I used a 47 ohm resistor, still hot and no dimming!
i used a 22 Ohm resistor and it is warm and dimming not working so good...

supposed that the biggest the resistor the less the current...
Driver led and pwm too confused...

[budm]

Re: Toshiba 32W1343DG No Backlights, Flashlight Test OK, TV is already broken

It is constant current source, so it will try to maintain the constant current through the LED string or the load.
For example. 100mA constant current source connected to 100 Ohms, the power supply will try to force 100mA through it so the Vdrops on the resistor will be 10V, then the power dissipation of will be 1W.
Now if you connect 10 Ohms resistor instead withe constant current of 100mA, then the Vdrops on the 10 Ohms resistor will be 1V, power dissipation then will be only 0.1W
As you can see when you use resistor in place of semiconductor, the Vdrops will vary with the amount of current flowing through it, the semiconductor will practically maintain the forward bias junction Voltage when the current flowing to it is varied.
So using resistor in place of semiconductor will not really work well because the Vdrops is not constant so the total Vdrops of the LED string will not be constant, the resistor that is in series with PWM Controlled MOSFET and the LED string is used as the current sensing to maintain the constant current.

[bily-78]

Re: Toshiba 32W1343DG No Backlights, Flashlight Test OK, TV is already broken

I have the same problem. 4 short and 1 burned out LEDs. Replacyng only LEDs with 3528 1W. Working fine. This picture is with warm white LEDs, but i replace it with cool white. Here is the full schematic of this TV.

[bily-78]

Re: Toshiba 32W1343DG No Backlights, Flashlight Test OK, TV is already broken

I recommend to reduce LEDs current. Originally in this TV current was 100mA :
R iset= R155 + R157 = 4K7 + 4K7 = 9,4kOm.

By incerting 2,2kOm i reduce LED current to 80mA :
R iset= 4K7 + 4K7 + 2K2 = 11,6kOm

[eltrash]

Re: Toshiba 32W1343DG No Backlights, Flashlight Test OK, TV is already broken

Thanks for your replies and congratulation for sucessfully repairing. My repaired TV (June 2016) is still working fine, i use it daily.