Toshiba 55LF621U19 firetv

[vikingTv]

So I acquired a toshiba 55" 4k fire tv, 55LF621U19.
I got this for free from someone who was like if you can fix it you can have it.

I turn it on get a single flash, power light pulses and then it turns off. No logo, no picture or anything. I'm still pretty new to the whole fix tv thing, but I love to tinker. I know from some previous tv's that I think what happens is it's an LED protection thing, i.e. the circuit tries to initialize the LED backlights and something is off and it goes into protection mode.

I've fixed this before by finding the bad/shorted backlight, replacing it and then all is well. I already have some toshiba backlight strips from another cracked screen tv that I could repurpose so I tear the tv apart. and to my surprise (I did say i'm kinda new to this) every single backlight tests fine. I was able to use my backlight tester and fire all of them up, all of them measure the same voltage (2.7).

So i button the tv back up. What should I investigate next? I'm just like the TV was made in 2018 it's practically brand new and If i fix it was gonna give it to a friend of mine who needs a tv and has been hit a bit hard by the current times.

I don't have pictures just yet, working on it. but it has a power board (which also powers led's) a main board and a t-con board.
this is the main board: https://www.walmart.com/ip/Toshiba-5...0010/955844042
this is the power board: https://www.walmart.com/ip/Toshiba-5...640I/334062590

note, i found these boards cheaper elsewhere, the power board i can find for 29 bucks. anyhoo some direction on next steps would be great.
thx!

[CapLeaker]

Re: Toshiba 55LF621U19 firetv

You have to test all the pins that go from the PSU to the main board. The pin out legend is on the corner printed on the PSU. Turn the TV on and check all voltages on these pins and write them down like this:

Pin1 PSon = 3.5V
Pin2 GND = 0V
etc.
We need to know what voltages are on which pin and the function of the pin.

Sounds like STBY is O.k, since the TV tries to power up. So either there is a problem with the backlights, or a voltage rail is missing on the PSU.
You can force the PSU on without the main board connected, but the backlights stay plugged in. All you have to do is to put a 1k resistor between STBY and PSon, another 1k resistor form STBY to BLon and plug the tv in. All voltage rails should be up and the backlights should be on. You may have to also put STBY to the DIM pin.

Try it and report back.