Please HELP Rca led50b45rq

[zblad]

Hello all,

I have been working on an Rca led50b45rq and am completely stumped. The issue is the tv turns on for a split second and the powers off. I have tested all the voltage and I have tried swapping out the power supply and mainboard. The issue seems like it would be the led strips but they all turn on just fine. If I plug the tv in I get a small red led hit power red led shuts off and then tv backlight come on for about 1 second and then tv shuts down. The red LED remains off. I unplug the tv plugs it back in and the red led is back on. Now here is the weird part if I unhook the led strips power and plug the tv in small red led comes on I hit the power button led goes off wait 5 seconds obviously cant see any screen because the leds are unhooked, I hit the power button and the red led comes back on like it shut down properly. Basically why does the tv seems to work fine with the leds unhooked but powers off if they are hooked up.

Thank You,
Zach

[budm]

Re: Please HELP Rca led50b45rq

"The issue seems like it would be the led strips but they all turn on just fine" May I ask how you verify that?
Pictures if the all the boards and the whole back side of the TV so we can see how all the boards are connected together?

[zblad]

Re: Please HELP Rca led50b45rq

Here is a picture of all them on I will get one of all the boards in a few minutes.

[budm]

Re: Please HELP Rca led50b45rq

Ah, you already took the panel apart.

[zblad]

Re: Please HELP Rca led50b45rq

Here are the boards

If I unhook the left leds that are in series it doesn't change anything
If I unhook the right leds that are in series it doesn't change anything

If I unhook both at the same times the tv looks like it works fine as far as powering on and off.

Its almost like the leds are either drawing too much or too little power because they all work. But for that to make sense that would mean both sides are messed up.

[dick_barton]

Re: Please HELP Rca led50b45rq

I'm not 100% sure of this but considering that all the leds are on in your photo, they don't appear to be as blinding in brighness as in other photo's posted of the back panel leds being on. Just a thought.

[budm]

Re: Please HELP Rca led50b45rq

Yea, I wonder what DCV he is getting at the L+.
Ref. to this thread:
https://www.badcaps.net/forum/showth...Rca+led50b45rq

[zblad]

Re: Please HELP Rca led50b45rq

I checked voltages about a month ago and if I remember right it spikes up and then fizzles down to like 30v and then drains down. That's why I thought it was the powerboard but I swapped that out and still did the same. Only thing that makes a difference is unhooking the led strips... I completely lost on what it is. Thought about hooking just one strip up to each side but will that be too much power to the strip and zap the leds?

[zblad]

Re: Please HELP Rca led50b45rq

So maybe we should take a step back when i got my powerboard it was used and the fuse was blown so i swapped fuses and the tv did the same thing. The voltages of both L+ and L- are similar. When I tried a different main board it wasn't exactly the same model number not sure how much that would matter because it did a similar thing if i remember right. All the LEDs work so i feel that can be eliminated so what board would it most likely be if you had to guess...

[zblad]

Re: Please HELP Rca led50b45rq

im confused why L- has voltage isn't that ground? or what does the L- and L+ do?

[budm]

Re: Please HELP Rca led50b45rq

L+ is the Anode side of the LED string which is fed by boosted Voltage from the boost converter circuit, the L- Cathode is the return side of the LED string which is connected to the PWM controlled power MOSFET and then through the current sensing resistor in which the Vdrops on the resistor is used for maintaining the constant current through the LED string.

[zblad]

Re: Please HELP Rca led50b45rq

So the L+ voltage is what powers the LEDs... Is there anyway I could turn the LEDs on with a separate power supply if so how many volts would I need? Or is there anyway I can trick the tv from powering off? Or what board do you think is causing the issue?

[dick_barton]

Re: Please HELP Rca led50b45rq

Have you checked Con4 to see that you have the Backlight ON signal from the main board. Can you force the backlights on using that pin connected to Vstby?

[zblad]

Re: Please HELP Rca led50b45rq

Have you checked Con4 to see that you have the Backlight ON signal from the main board.

How would I go about doing this just ground out my black prong on my voltage meter and put red on con4 im guessing?


Can you force the backlights on using that pin connected to Vstby?

How would I force it do I ground that pin out or ...

Thanks for the help

[dick_barton]

Re: Please HELP Rca led50b45rq

Start with just checking the voltages on Con4
Con4
Pin 1 = GND
Pin2 = ADJ
Pin3 = BKL

With black lead on chassis measure the voltage on the 3 pins using your red lead.

[zblad]

Re: Please HELP Rca led50b45rq

Alright I am going to do my best at describing this....

BLON - Stays at 0 hit power button and doesn't change until the LEDs flash then it gets 5v for a second and falls back down to 0sh.

ADJ - Stays at 0 hit power button and it goes to 5v and stays there until LEDs flash and then falls back down.

GND - Stays 0 the whole time.

If I unhook the little plastic connector with 3 wires I cant turn the tv on and off with no LEDs. But it atleast doesn't go into the protection mode or whatever you would call it...

[zblad]

Re: Please HELP Rca led50b45rq

Can you force the backlights on using that pin connected to Vstby?

I think I get what your saying just unplug both ribbons and run a jumper from vstby to con4 BLON and see if they stay on?

[zblad]

Re: Please HELP Rca led50b45rq

OMG IT WORKED!!!! If I plug the tv in power it on and jump from VSTBY to the BLON they stay on just fine. So I don't know if its the powerboard or the mainboard at fault I would assume the mainboard.

[dick_barton]

Re: Please HELP Rca led50b45rq

The mainboard should provide the voltage to BLON. So that is missing for some reason. Reconnect everthing and then check what voltage you have at BLON when you switch out of standby.

[dick_barton]

Re: Please HELP Rca led50b45rq

If you can force the backlights on and they appear to be OK then it looks as though it is a mainboard fault. Can you post a really sharp picture of the mainboard. It would be worth seeing if there are any voltage regulators on it that could be checked out.