toshiba 50L1350U no backlight

[budm]

Re: toshiba 50L1350U no backlight

ok ill put these two resistors back in and pull that wire, and report back.
thanks.
so without the pwm, the screen will just be at the max brightness or what?
just curious

Yes. The PWM signal is about 150~300 Hz range, 5V signal, min is 10% (0.5VDC average) pulse width equal min brightness, 90% (4.5VDC average) pulse width equal max brightness. Your is at 0.232V way below the 10% requirement.

[sdinelli]

Re: toshiba 50L1350U no backlight

pulled that pwm wire, nothing happened.

[dcaron614]

Re: toshiba 50L1350U no backlight

i dont understand why LEd's need so much voltage.

I'm not sure about how much they require. I got the TV from a guy($20 bucks) who said sound no picture, so when I got it home and did the flashlight test I figured I would just have to change the led driver, but once opened up notice there wasn't one. Did a quick Google search and the Toshiba website popped up with people with this model having the same issue and the Tech said replace the pwr board, so I found one on ebay cheap so I took that gamble. then after seeing your post on here I tested the L1+ and L2+ and notice the same reading, but It would jump to 122v on start up for that hot second then go to 77v after the backlight flash and went out. pwr board came in popped it in then all was good.

[budm]

Re: toshiba 50L1350U no backlight

pulled that pwm wire, nothing happened.

It still flashes and then goes off or not even flash on at with the PWM wire removed?
you can try new power supply board like dcaron614 did.

[sdinelli]

Re: toshiba 50L1350U no backlight

I'm not sure about how much they require. I got the TV from a guy($20 bucks) who said sound no picture, so when I got it home and did the flashlight test I figured I would just have to change the led driver, but once opened up notice there wasn't one. Did a quick Google search and the Toshiba website popped up with people with this model having the same issue and the Tech said replace the pwr board, so I found one on ebay cheap so I took that gamble. then after seeing your post on here I tested the L1+ and L2+ and notice the same reading, but It would jump to 122v on start up for that hot second then go to 77v after the backlight flash and went out. pwr board came in popped it in then all was good.

nice, ill see if i can find one that cheap. cheapest i saw was 60something i think.

[sdinelli]

Re: toshiba 50L1350U no backlight

It still flashes and then goes off or not even flash on at with the PWM wire removed?
you can try new power supply board like dcaron614 did.

i didnt notice a flash, ill try again n see. it was still at 77V so thats def a problem. ill check the caps.. have you seen them go bad this fast? the sets not, THAT old.
Wish i could find a service manual. cant find anything on this model.

I tried again and no flash

[dcaron614]

Re: toshiba 50L1350U no backlight

nice, ill see if i can find one that cheap. cheapest i saw was 60something i think.

This guy has one for 45 free shipping(1st link)... I hope this fixes ur issue also.. the guy I got mine from had 19 of them all gone now.. But I will give you his link also just in case he gets more (2nd link)

http://www.ebay.com/itm/Toshiba-7503...item4196a750ff



http://www.ebay.com/itm/391102002943...%3AMEBIDX%3AIT

[sdinelli]

Re: toshiba 50L1350U no backlight

This guy has one for 45 free shipping(1st link)... I hope this fixes ur issue also.. the guy I got mine from had 19 of them all gone now.. But I will give you his link also just in case he gets more (2nd link)

http://www.ebay.com/itm/Toshiba-7503...item4196a750ff



http://www.ebay.com/itm/391102002943...%3AMEBIDX%3AIT

thanks man i appreciate it.

[budm]

Re: toshiba 50L1350U no backlight

I am still curious about the PWM signal that drops out, not sure it drops out due the some kind of feedback signal from the power supply/LED driver to tell the main board to shut down the PWM due to the problem in the power supply/LED driver board. No service manual to study how this TV function.
The typical symptom of failed LEDs has the same indication that the LED drive output Voltage goes high and then the protection circuit kicks to so the out put Voltage will drop.
So I hope that the new power supply/LED driver board will fix your problem.

[sdinelli]

Re: toshiba 50L1350U no backlight

the bigger diode in the middle of the board, next to the heat sink, gives me a voltage when measured reverse bias.
It measures OL when out of circuit. do you think this can be an issue?

[sdinelli]

Re: toshiba 50L1350U no backlight

so i tested the 4 caps on the left side ( capacitance, not esr)
and i found 2 which were rated at 56uf and tested at 47uf.
also, i tested the main filter cap, rated 470uf and tested 441uf

its not below the 20% line, but do you think it will bring down the back light voltage?

[rican199]

Re: toshiba 50L1350U no backlight

Having the same issue did the flashlight test blacklight is out on mine. I went ahead and purchased a new power supply board, just got it in today. Installed the board....needless to say same issue , I just purchased a t-con board since I don't have a multi-meter to test. Could this be the issue?

Thanks in Advance

[Agent24]

Re: toshiba 50L1350U no backlight

T-Con has nothing to do with the back lights.. if a new PSU didn't fix it (and you know the new PSU is good), suspect the LEDs themselves. Could also be mainboard though.

[rican199]

Re: toshiba 50L1350U no backlight

I didn't know the mainboard could also create an issue with the blacklights. Everywhere I have read said either the t-con or power supply. The mainboard does not connect to the LED's. How could it be?

T-Con has nothing to do with the back lights.. if a new PSU didn't fix it (and you know the new PSU is good), suspect the LEDs themselves. Could also be mainboard though.

[budm]

Re: toshiba 50L1350U no backlight

I didn't know the mainboard could also create an issue with the blacklights. Everywhere I have read said either the t-con or power supply. The mainboard does not connect to the LED's. How could it be?

The main board generates the BL-ON signal to turn on the backlights circuit, it also generates PWM Dimming control signal (if the PWM signal is stuck LOW, then you will not have backlights either, both bl-on and the PWM signal have to be present, 10% Pulse width =,min backlights level, 90% pulse width = max backlights level, if it goes below 10% then there will be no backlights).
Some TV will use the signal from the T-CON to control the backlights level based on the Video signal, it is called Dynamic Contrast so they can claim the TV has 100 thousand : 1 which is a fake contrast spec.
Is there a small cables between the T-CON and the backlights circuit?

[Agent24]

Re: toshiba 50L1350U no backlight

I didn't know the mainboard could also create an issue with the blacklights. Everywhere I have read said either the t-con or power supply. The mainboard does not connect to the LED's. How could it be?

The mainboard doesn't connect to the LEDs, but it does control the LED drive circuit. If the mainboard is faulty and doesn't tell the LED driver to come on, then the LEDs won't come on either.

The LEDs themselves often go faulty, though.

Some TV will use the signal from the T-CON to control the backlights level based on the Video signal, it is called Dynamic Contrast so they can claim the TV has 100 thousand : 1 which is a fake contrast spec.

Oops, didn't know that.

[rican199]

Re: toshiba 50L1350U no backlight

There are 2 ribbon cables that connect to the LED but a thin cable that connects from the power supply to the LED as well hence the reason for replacement.

The main board generates the BL-ON signal to turn on the backlights circuit, it also generates PWM Dimming control signal (if the PWM signal is stuck LOW, then you will not have backlights either, both bl-on and the PWM signal have to be present, 10% Pulse width =,min backlights level, 90% pulse width = max backlights level, if it goes below 10% then there will be no backlights).
Some TV will use the signal from the T-CON to control the backlights level based on the Video signal, it is called Dynamic Contrast so they can claim the TV has 100 thousand : 1 which is a fake contrast spec.
Is there a small cables between the T-CON and the backlights circuit?

[budm]

Re: toshiba 50L1350U no backlight

There are 2 ribbon cables that connect to the LED but a thin cable that connects from the power supply to the LED as well hence the reason for replacement.

So are you getting the BL-ON and the PWM signals feeding the power supply board or not?

[rican199]

Re: toshiba 50L1350U no backlight

Not sure, don't have a meter to check, I can get one but wouldn't know what to look for or what to test, this is my first led tv issue. Sorry

So are you getting the BL-ON and the PWM signals feeding the power supply board or not?

[budm]

Re: toshiba 50L1350U no backlight

Without having a basic tools to at least testing some Voltages, then all you can do is to keep replacing the boards until the TV starts working again, but if you do have bad LEDs then you will hope you can return the boards back to the sellers.