toshiba 50L1350U no backlight

[rican199]

Re: toshiba 50L1350U no backlight

Yes that's the reason I'm keeping all the boxes, le it's the actual Led strip is there a way to replace them or are all hopes lost? I mean I spent $500 on this TV new and so far total cost spent fixing it has totaled $50 so I'm good so far. A mainboard would run between 50-100 plus shipping. So far I have purchased a power supply $40 and now the t-con board $8 all new items. Just waiting on T-con board which should be here on the 5th.

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.

[Agent24]

Re: toshiba 50L1350U no backlight

The LEDs are replaceable, it's just a trickier job than replacing boards. You have to take the panel apart and then find some new LEDs (the hardest part it seems).

Some have bought LED strips pulled from other TVs, but you can also replace the individual LEDs too. However, from what I read before, it's hard to get new LEDs that exactly match the old ones for colour\brightness etc...

Replacing the LEDs is not impossible though.

[fishmanstan]

Re: toshiba 50L1350U no backlight

Yes that's the reason I'm keeping all the boxes, le it's the actual Led strip is there a way to replace them or are all hopes lost? I mean I spent $500 on this TV new and so far total cost spent fixing it has totaled $50 so I'm good so far. A mainboard would run between 50-100 plus shipping. So far I have purchased a power supply $40 and now the t-con board $8 all new items. Just waiting on T-con board which should be here on the 5th.

Did replacing the T-con board fix this?

[rican199]

Re: toshiba 50L1350U no backlight

Did replacing the T-con board fix this?

Nope...about to order the main board this weekend. So far have replaced all boards except for the main board, I think it costs between 50-60 bucks so it's not bad.

[fzabkar]

Re: toshiba 50L1350U no backlight

Excuse my ignorance, but how does the PWM function work on this board? Are there components on the underside of the PCB?

Also, I can see 4 optocouplers but only 3 regulators (5.1V, 12V, HV).

Does SCR201 provide protection?

Here is a hires image of the PSU PCB:

http://assets.shopjimmy.com/media/ca...033153-top.jpg

Edit: Actually I see 2 regulators, but U501 controls both the 5.1V and 12V supplies, so it only requires one optocoupler. So what do the other 2 optocouplers do?

Edit #2: Perhaps one optocoupler provides the AC_Detect function.

Just FYI ...

FSB117H, Fairchild, mWSaver Power Switch, 1A, 700V SenseFET, DIP-8:
https://cdn.badcaps-static.com/pdfs/...e8e0f7d20c.pdf

[sdinelli]

Re: toshiba 50L1350U no backlight

before i spend money on a new PS board, can i test the LEDs with a dc power supply by applying voltage to L1+ and/or L2+?
If so, what voltage and amp should i apply. do you think i can determine with out taking the panel off?

[sdinelli]

Re: toshiba 50L1350U no backlight

or i had an idea.. if my pwm is too low an dis the culprit, can i try to apply some voltage on that line to see if it comes on? what that be safe?

[rican199]

Re: toshiba 50L1350U no backlight

Does anyone know where I can purchase the mainboard, been looking for the past few weeks and have ended with either in backorder or not available.

Any assistance would be appreciated!

Thanks!!

[rican199]

Re: toshiba 50L1350U no backlight

An update...so I finally purchased the main board but to my luck this did not fix the tv. All boards are new and working. To my conclusion the LED lights went 👎 and I will not be spending any cash on those bad boys. So anyone interested on these parts I will be posting them on eBay in the next few days or reach out to me on here and we can probably come to an agreement. Well black Friday is near....time to look for a 📺.

Happy holidays people!

[Martinacan]

Re: toshiba 50L1350U no backlight

Hi
I am new to this forum
I have a Toshiba 50L1350U that has no back lights
I have replaced the power supply board with a new one... no changes.
The output from the power supply to the LED array is on L1 to ground 80.5 VDC & L2 to ground 80.5VDC...
The voltage is the same with the LED array plugged in or unplugged..
I have 2.73VDC on pwm.. I tried unplugging the wire - no changes no LED backlights...
Can I assume that I have faulty LEDs?
Just before the LED backlights stopped working, the LED lights on the top and bottom rows were dimmer than the middle portion

[Martinacan]

Re: toshiba 50L1350U no backlight

Is 80.5VDC enough voltage for the LEDs...
I noted that an earlier post a person had 77VDC before replacing the power supply.. the Voltage was 113VDC with a new power supply. The board indicates the voltage is listed as 111VDC.. I assume this would be true at full brightness

[budm]

Re: toshiba 50L1350U no backlight

You need to leave the meter probe on L1 then turn on the TV to see if the Voltage will jump up and then comes back down after couple seconds.

[Martinacan]

Re: toshiba 50L1350U no backlight

Hi Budm
Yes the voltage peaked at 134 VDC when the TV was first turned on, then dropped down to 79.5 VDC.
I did get another power supply.. But this didn't solve my problem... but this new power supply is one from another TV...

[budm]

Re: toshiba 50L1350U no backlight

That means you have open circuit in the wiring, connector to the LED strips, bad LED (which is very common failure). It goes into shutdown due to no load so the Voltage goes up too high and trip the protection circuit.
79VDC is the feeding Voltage to the LED power supply boost converter circuit, the boosted Voltage is then feed the LED strings, the current through string and the sensing circuit are done through the LED driver IC.

[Martinacan]

Re: toshiba 50L1350U no backlight

I did check continuity with wire connector from the power supply to the LED terminal strip & the continuity along the terminal strip to the beginning of each LED strip - all good...
So it would appear that I have failed LED(s)... I'm not sure if its worth replacing the LED array - I hate to put the money out only to find I have another problem

[Martinacan]

Re: toshiba 50L1350U no backlight

If anyone is looking for good power supplies, main board & a good T-con board - please let me know!

[Shatch]

Re: toshiba 50L1350U no backlight

I have BL_ON and PWM on start. Backlights flash. PWM drops to 232mv. No Backlights. I removed the PWM wire and the backlights don't flash on. L1 and L2 is at 77 volts. At first it is 110volts then drops down as the PWM drops out. Any ideas to eliminate good from the bad ? The power supply voltages all look great. Any ideas to test the backlights themselves ? Thank you

[budm]

Re: toshiba 50L1350U no backlight

The backlights will not come on if the PWM is at that low level even you have the BL-ON signal.

[Shatch]

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.

[Shatch]

Re: toshiba 50L1350U no backlight

I'm thinking it's either the main board or the lights themselves.