LG 55uj6200 wont turn on

[microvibe]

I have lg 55uj6200, when plugged in its in standby to turn on you have press power button multiple time then it flashes 3 times and turns on but no video(flash light test) no backlights no sound.

Powers supply
Stby pwr on
13.5v 12.5v 13.2v

Pwr on 3.5v 3.5v
Pdim .47v .47v
Inv on 0v 0.05v

If i force power supply turn inverter on backlights work no video.

Is it possible trbl shoot backlight inv on circuit on main board or is this case bad bga chip or mainboard?

[nomoresonys]

Re: LG 55uj6200 wont turn on

Best bet is probably a replacement mainboard.

[dick_barton]

Re: LG 55uj6200 wont turn on

PWR ON and INV ON are mainboard signals sent back to the power supply. It looks like the mainboard has problems

https://www.shopjimmy.com/lg-55uj620...air-parts-kit/

[Tom1974]

Re: LG 55uj6200 wont turn on

Hi guys. I have similar issue as microvibe, no picture but hear sound. I tested the led strips and found one bed led. I replaced the led strip. When i powered on the tv backlights still didnt come on. But when i swithed it off half the strips flash once. The other led circuit doesnt respond at all.
I checked the voltages. I got 13.2 volts going to the mainboard but no voltage measured in connection to leds.
I purchased a new powerboard. When i power it on without leds or main board connected i still dont measure any voltage to the led connection. Same result when i connect those two. No when switching tv on or off leds dont flash at all.
Is there something im doing wrong or i got a new faulty power supply board?
Also i checked fuses. Problem is i see only two fuses. F1 and F3. Where is F2? LOL

[nomoresonys]

Re: LG 55uj6200 wont turn on

do the flashlight test, see if there's an image, hit the menu if needed see if you can see any text or anything.

[dskall]

Re: LG 55uj6200 wont turn on

You are checking led voltage right at turn on? Compare old and new power board for voltage. What is inv_on voltage in standby and power on.

[neilc6]

Re: LG 55uj6200 wont turn on

Hi guys. I have similar issue as microvibe, no picture but hear sound. I tested the led strips and found one bed led. I replaced the led strip. When i powered on the tv backlights still didnt come on. But when i swithed it off half the strips flash once. The other led circuit doesnt respond at all.

You still have a backlight problem. When you do backlight replacements, you should replace all the strips with new and turn down the backlight level for all inputs and apps. You can test the new strips by turning on the TV with panel disconnected before reassembling the TV.

[Tom1974]

Re: LG 55uj6200 wont turn on

I will re-assemble tv tomorrow to check the flashlight check for the main board. I connected all the new led strips with the same problem, non will light up. What did you meam by inv on voltage? I had tv powered on and off with the same results measuring only under a volt on both led+ with the minus connected to ground using the tv housing.

[neilc6]

Re: LG 55uj6200 wont turn on

LG TVs have shutdown protection of the backlights if the sensed voltage is out of range due to shorted LEDs. The backlights should flash (if there isn't an open circuit) with a corresponding spike in voltage at the LED connector. You need to check continuity to the strips to make sure there isn't a bad connection to the strips. A LED tester at the backlight connector can confirm this. The main board also sends a logic backlight on signal to turn on the backlights which you can confirm but this is less likely the problem.

[Tom1974]

Re: LG 55uj6200 wont turn on

Hi. I got the led tester. I found two led on one strip coming on slow. I replaced all the led strips now. With the led tester they all come on and sho 68v going thru both strips. Reassembled the tv. When power on tv still no backlight come on, but i have sound, and with a flashlight i confirm tv has the menu showing.

[Tom1974]

Re: LG 55uj6200 wont turn on

Therevis no voltage in the led connector at all. I checked the two transformers. The smaller one input 12v i measure 0. On the output of 18v and the two 400v connection i get 0v AC. Same measurement on both the old Nd the new power board.

[Tom1974]

Re: LG 55uj6200 wont turn on

LG TVs have shutdown protection of the backlights if the sensed voltage is out of range due to shorted LEDs. The backlights should flash (if there isn't an open circuit) with a corresponding spike in voltage at the LED connector. You need to check continuity to the strips to make sure there isn't a bad connection to the strips. A LED tester at the backlight connector can confirm this. The main board also sends a logic backlight on signal to turn on the backlights which you can confirm but this is less likely the problem.

How can i check if the mainboard sends that logic signal? Is ot possible the mainboard is not doing this?
Is there a reset function i could trigger to restart the voltage flowing to the leds again?

[dskall]

Re: LG 55uj6200 wont turn on

You have a pin on connector labeled Inv on. What is voltage of this pin in standby and when powered on?
If voltage doesn't change you can try heating up processor chip and try turning on tv.

[Tom1974]

Re: LG 55uj6200 wont turn on

You are checking led voltage right at turn on? Compare old and new power board for voltage. What is inv_on voltage in standby and power on.

Inv on is 3.2volts turned tv on
Inv on is 0volt tv turned ofi suppose invon you meamt and i found only on the connector going from power board to main board

[dskall]

Re: LG 55uj6200 wont turn on

Need some clear pictures of front and back of power board.

[captainKKK]

Re: LG 55uj6200 wont turn on

What is the voltage on the two main caps....be careful