Lg 47lw5400

[ludespeedny]

I recently acquired a LG 47lw5400 that screen doesn't power on. When I power it on the power light goes from red to blue, but I don't get a display. I checked the power board for bad caps, but all appear to be fine. Could someone recommend the next steps to take to figure out if it is the main board that needs replacing or the t-con board?

Here are pics of the mainboard and power board (sorry, I didn't get any of the t-con board yet).
https://picasaweb.google.com/1023660...eat=directlink

[ludespeedny]

Re: Lg 47lw5400

Sorry meant it is the 47lw5300

[zdsh07p9]

Re: Lg 47lw5400

The next step for me is checking to see if you can still see a picture when you shine an LED or flashlight onto the screen. If you can see a picture then something is wrong with your backlight inverter which looks to be a part of that power board if im not mistaken. Sometimes the backlight inverter goes out and you just cant see the picture because there is no light behind it to present it to you. So check this first - others may chime in.

[ludespeedny]

Re: Lg 47lw5400

Ok, I'll try that tonight

[zdsh07p9]

Re: Lg 47lw5400

I'm no professional - but I have repaired plenty of TVs and that is what my next step would be. If you can see a picture moving behind it (and it will be kind of hard to see) then I would suggest you replace whatever powers the backlight - whether it be that power supply (which I think it is) or what they call the inverter boards. In this case I think your power supply is also an inverter board that powers the backlights.

[ludespeedny]

Re: Lg 47lw5400

Do you know if that is the case if I can replace components on the board or just buy a new board?

[budm]

Re: Lg 47lw5400

Your TV uses LED backlights so it does not have inverter board like the TV with CCFL backlights.
Most common failure we see around here for the LED backlights TV are due to open LED on the backlights LED string.
We need to verify that if we do have BL_ON signal or not, if we do, then we will need to see if we have voltages in the LED driver circuits.
Looking at the board, it looks like it has 12 LED strings.
I need the pictures of the whole backside of the TV, since this TV has dynamic contrast control to dim each string of the LED so there should be a cable between the T-CON board and this power supply board so the T-CON will control how the LED are lit. You can try disconnecting this cable to see if the backlights will come on, we need to verify if that is the setup for this TV.

[ludespeedny]

Re: Lg 47lw5400

Ok, looks like there is nothing on the screen and doesn't seem that the audio works either. I tried playing a Blu-ray and switching inputs but got nothing. Also, the backlight doesn't work on powerup either.

[ludespeedny]

Re: Lg 47lw5400

How can I test the fuses on the power board? I tried and didn't get anything on them , so maybe I am doing it wrong, what should I set the multimeter to and what should I expect back?

[ludespeedny]

Re: Lg 47lw5400

I tested the voltages on this board: https://picasaweb.google.com/lh/phot...eat=directlink
and most were close enough to spec. The 12v were about 11.9 the 3.5v were about 3.45 and the 24v was about 24.4. So it would seem like the power board is ok.
What do I check next?

[RCA2000]

Re: Lg 47lw5400

Ok-- if all of your run voltages are good--check and see if the "BL on" line is coming up, that turns on the LED drivers on the PS. Your set has a bunch of transistors on the top of the board, near those 2 big connectors--that drive the LED strings.

But--if you are getting NO picture info, even if shining a light source onto the panel--and if this set uses a T-con-- you need to see if it is working--BTW_-to trigger "dynamic dimming" of the indivudual LED strings--the T-con gives a signal to the BL control, and without that--it might not come on at all.

ALso--make SURE the ribbon connectors to the T-con are in good order.

It IS possible--to test the individual LED strings--IF you are getting the B+ voltage to them. It should show on the connector for the LED strings, likely about a 150-200 volt supply. Those transistors all gate the voltage from the strings to ground, depending on how bright they need to be--they are brought closer to ground.

Take a 220 ohm 1 watt or so resistor, and VERY carefully, probe the pin on each string, where it goes to each driver transistor, and touch the OTHER end of the resistor to GROUND, for a second, and see if that string comes up. Do this for each string--until all have checked ok. DO NOT do this for long--that resistor will get HOT--so only do this for a few seconds--long enough to test the strings.

DO NOT--simply touch ANY string directly to ground without that resistor--or you WILL blow a perfectly good LED string out.

[ludespeedny]

Re: Lg 47lw5400

Yeah, I have no display so not sure how to tell if online.
Ribbon connectors look fine.
So to see if they get voltage, I should put the positive on the B+ and negative on any ground?

[RCA2000]

Re: Lg 47lw5400

If the LED strings are good--you will likely see pretty much the same voltage on the strings as the b+--UNTIL they are active. At that point--the voltage will drop as each diode then lights and draws current. If you see 0 voltage on ANY string but have the b_ for that set---then that string has an OPEN LED_-not real uncommon.

[budm]

Re: Lg 47lw5400

So do you have the pictures of the whole back side of the TV so we can see how all the boards are connected together?
Open LED String indicator:
https://www.badcaps.net/forum/showpo...&postcount=107

[ludespeedny]

Re: Lg 47lw5400

Here is a pic of the back: https://picasaweb.google.com/lh/phot...eat=directlink
I think the led's are actually built in the screen but not sure.

[ludespeedny]

Re: Lg 47lw5400

So I got a mainboard and partial success. It will power on but has these lines on the tv, and never fully boots, it stays steady for a bit, then flashes and eventually will power off. Any suggestions?
https://picasaweb.google.com/lh/phot...eat=directlink

[ludespeedny]

Re: Lg 47lw5400

Is it possible a bad t-con would prevent the tv from fully booting?

[galrock]

Re: Lg 47lw5400

hey there i have a similer model only 42",
only thing i can tell is that the relay clicks on and of and 24v pops for a second to around 45v, also 3.5 is present, is there a way to check the psu in stand alone and the led strips in standalone

[galrock]

Re: Lg 47lw5400

just to let everybody know cap c271 was shorted, hence 24v was grounded, just so that this will be public in case someone will encounter this in the future

[ludespeedny]

Re: Lg 47lw5400

So just got a replacement t-con board today and same results. Is it possible the mainboard I got was bad?