toshiba 50L1350U no backlight

[budm]

Re: toshiba 50L1350U no backlight

Are you getting the same DCV reading as in post 52, 53?
Since your backlights did flash on, that means the booted Voltage is working but it goes into shutdown somehow which either due to open circuit or over current.

[Shatch]

Re: toshiba 50L1350U no backlight

Yes I'am

[michael dranfield]

Re: toshiba 50L1350U no backlight

Thanks for the response budm. I tried removing the PWM wire and applying 3.2 volts . It didn't help. I guess I need it pulsed. I trying to think what I have to get 110 to 120 volts DC to test the lamps.

I have a bench power supply 0-300v at 0-200ma for this job , however if you are only doing a one off job you can make a simple test jig to simulate the LED panel loading by wiring a load of while LED S in series, so for say 80 volts LED Vcc you would need 22 LED s in series , you can buy a hundred of these on e bay for a couple of pounds and its much cheaper than just buying replacement boards to provide a diagnosis of the fault.

[michael dranfield]

Re: toshiba 50L1350U no backlight

Are you getting the same DCV reading as in post 52, 53?
Since your backlights did flash on, that means the booted Voltage is working but it goes into shutdown somehow which either due to open circuit or over current.

Dont assume the backlights are not faulty just because they flashed at switch on, I had a set doing just this and it was the backlights that were faulty.

I have even had a set that went off intermittent every 3-4 days and when I stripped the panel down and powered it up 2 leds were not lit but the rest were ..

[ReeceyBurger123]

Re: toshiba 50L1350U no backlight

Dont assume the backlights are not faulty just because they flashed at switch on, I had a set doing just this and it was the backlights that were faulty.

I have even had a set that went off intermittent every 3-4 days and when I stripped the panel down and powered it up 2 leds were not lit but the rest were ..

I agree 100% I had a 42" Lg edge lit type with an intermittent Led and that was a fucker to diagnose. Will link thread.

[ReeceyBurger123]

Re: toshiba 50L1350U no backlight

Here is the thread, I did not do a Yt video on the Tv as it was very hard to diagnose. I did suspect the driver as I had weird readings but was an Led in the end:

https://www.badcaps.net/forum/showthread.php?t=49960

Note the failed Led in mine had a very small crack in the dye, this is visible when looking very closely so guessing that caused was causing an intermittent connection.

[budm]

Re: toshiba 50L1350U no backlight

Dont assume the backlights are not faulty just because they flashed at switch on, I had a set doing just this and it was the backlights that were faulty.

I have even had a set that went off intermittent every 3-4 days and when I stripped the panel down and powered it up 2 leds were not lit but the rest were ..

I did not assume anything, where did I say it may not be LED fault? as I said 'that means the boosted Voltage is working but it goes into shutdown somehow which either due to open circuit or over current.' If the LED strips are not connected in series and has more than one driver, you will get the flash from the working string, or if it has one big long string and some of the LEDs are shorted out causing the over current condition for the boost converter to go into shutdown (same for multi drivers.
I ready indicated the Boost converter is fine.
If you read post 6 you will know that this TV has two drivers for two set of the LED strings.
I have been doing electronics troubleshooting for over 40 years (Consumer Electronics, Industrial electronics, Semi-Conductor manufacturing (Fairchild Semiconductor for almost 10 years) and enough common sense as not to assume something. Fixed thousands of TV (from the all tubes days to solid state), monitors, audio pro and consumer equipment, etc.

[budm]

Re: toshiba 50L1350U no backlight

I do not know what is going on today, people is assuming something without reading from the beginning of the thread.
Just like this A hole on this thread:
https://www.badcaps.net/forum/showth...722#post635722

[Shatch]

Re: toshiba 50L1350U no backlight

I want to thank everyone for their help. I will try a bunch of LEDs to load test it. I'm working on this for a friend and trying to keep the cost down.

[Shatch]

Re: toshiba 50L1350U no backlight

I bought LEDS on ebay. I made two little wooden boxes up. Each box I drilled 36 holes. The LEDS are 3 to 3.4 volts. Someone posted the voltage to be 117v. So 36 would give me 108 to 122.4 volts. I hooked them up and turned the set on. The lights flash and go out. The lights stay out until I turn the set off, then they flash. Any ideas to eliminate the power board or the mainboard ?

[budm]

Re: toshiba 50L1350U no backlight

Your TV has two sets of LED strings with two set of LED drivers, so how many string did you have them hooked up to the LED drivers?

[Shatch]

Re: toshiba 50L1350U no backlight

I hooked up two separate units. I unplugged the LEDS to the TV screen, and soldered the wires to L1+ ,L1-, and the other to L2+ and L2-.

[budm]

Re: toshiba 50L1350U no backlight

So you bought individual LEDs 72 of them or LED strings?
Pictures?

[Shatch]

Re: toshiba 50L1350U no backlight

I'm having trouble with getting the pic posted.

[Shatch]

Re: toshiba 50L1350U no backlight

[budm]

Re: toshiba 50L1350U no backlight

So the PWM is still at mV range? Did it show higher than 2Vdc when the LEDs flash on and then drops to mV range?

[Shatch]

Re: toshiba 50L1350U no backlight

Yes. It starts at about 3.2 volts ,drops to 1.7 volts, then mv .

[Shatch]

Re: toshiba 50L1350U no backlight

I replaced the power supply board and the mainboard, no change. I took the back off the screen. There are 60 LEDs. 30 LEDs per string. I had 36 on each of my test boxes.

[Shatch]

Re: toshiba 50L1350U no backlight

One set of 5 LEDS are bad. I applied 15 vdc to each string of 5. I ordered the new strip. Looks like my test boxes with 36 lights caused the same fault as having a bad LED. When I get the new strip and get everything back together I will remove 6 lights and retest.

[budm]

Re: toshiba 50L1350U no backlight

It is hard to tell 100% for sure how many LEDs are actually on the strip without taking the panel apart, thanks for reporting what you found.