LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

[velorider562]

Hoping for some help diagnosing the problem with my TV so I don't just throw parts at it or the land fill. Its an LG 50UH5530, that after being unplugged for a few hours it will turn on and stay on for about 15 seconds, before shutting off. After that, when pressing the power button the red led will blink but the TV will not turn on. I have read the folllowing post that discribe very similar symptoms and followed the steps documented.

https://www.badcaps.net/forum/showthread.php?t=87284

Current Status:
STB pin on power board has 3.4v, always.
13.2 pin on power board have 6-9v
When first turning on before TV shuts down, 13.2 pins have 13.1-13.2 volts
When jumping STB with resistor 13.2v pins have 13.1-13.2 volts
When testing led strips with tester, all strips light up when viewing from the back of the tv and run at about 66v. I can't see the individual led since I have not remove the panel
When turning on with the led strip disconnected same thing happens
When turing on with TCON disconnected same thin happens
With the flashlight test is appear the LCD is not on, so it's more then just back light

The OP in the other thread eventaully replaced the led strips and resolved his problem. I have also read on Shop Jimmy that led failures are much more common then power board failures on this model.

So I can throw led strips at it but I'm hoping to confirm a diagnoses first. My concern is it appears that the main board is instructing the power board to shutdown, so either it's detecting some fault or the main board is faulty and shutting down.

I'm looking for suggestions to help me diagnoses the failure.

I have some expereince with hardware so I have good amount of tools, but I am far from an expert.

TV Background:
I picked up the TV off Nextdoor app. Two of the three HDMI ports had come off the mainboard, the original owner said it was like that for awhile and still worked. I resoldered one back on, the other the pins where too bent to resolder. If I can get the TV working and find the ports on DigiKey I'll resolder the remaining missing port later. The 3rd HDMI port that wasn't disconnected was loose, upon closer examination there was no solder on the mounting pins of the port, the only thing holding the port where the pins. The pads where not damaged, and I believe the original owner that the TV worked for quite a while like this so I don't think its related to the failure.

Thanks
John

[velorider562]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

I may have found the issue. I broke out the cheap usb microscope and was scanning the main board and I think found out burnt out caps. These cap are right in front of the tcon connector.

Any idea what specs these caps are?

[velorider562]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

Gets worse, went to desolder the cap and found another burnt component. Guess it just a new mainboard, but right now everyone is out of stock and they want close to $90 for it. Maybe the hdmi shorted some components.

Thanks
John

[diif]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

Have you checked those caps with a meter, they don't look burnt to me.

[DXseekerMO]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

I recently had this issue with this exact same model TV. I actually got it to run for a day and a half before the problem reared it's ugly head. After the screen went black with no picture I let it sit for 24hrs, turned the TV on and the picture remained on for about 10-15min.

When the screen went black the 13.2V pin had unstable voltage from about 7-10V.

Turns out one LED was breaking down after some time of use. Replacing the backlight strips fixed the problem. This model of TV is known for crap backlights.

If the backlights are the problem DO NOT, I repeat DO NOT install used LED strips and DO NOT replace the strips individually, replace them all at one time with a set from ShopJimmy.com.

It seems to me that when one LED goes bad in this model TV the remaining LEDs get stressed. Not replacing them all will very likely mean a repeat backlight repair.

[jason123]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

Gentlemen, I am having the same exact problem. Standby voltage is very unstable 8-12 V, when I turn the set on, it dips to 0 then 8 volts. You can see the LED on the main board that should remain red, is flashing on, then off. I had both the PFC and LED Driver ICs (bought on previous projects) so I replaced them and no luck. Replaced the backlight, and no change. Finally, I got a used Power Supply board from eBay, and the system is on and happy.
I'd really like to fix the power supply board if at all possible. Checked Caps, and Diodes, and FETs and nothing has "Failed" but I can't tell if they're weak.

The TV occasionally would start up for 1/2 hour or so.. then shuts off.
then, as long as it's plugged in, it is in the Cyclical unstable Standby voltage. Help is much appreciated.
Thanks

[nomoresonys]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

seems like bad voltage regulation on powerboard.

[nomoresonys]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

maybe a weak startup cap near the connector.

[jason123]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

Any idea which cap that is?

[nomoresonys]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

check c57, see what kind of voltage you have.

[nomoresonys]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

there's a dirty test to kind of tell if the caps are doing what they should, you put your meter on a high ohm setting then put a probe on each leg, it should rise or fall at a steady even pace, you can reverse the probe leads and should go in the other direction slowly and evenly, it's no replacement for a regular capacitance meter of course. Test is done with tv unplugged.

[R_J]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

I would try replacing C14 and see what happens. another suspect might be C5

[dskall]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

While you were changing controllers you should have changed your 13v controller. But it may just be bad cap or diode for the controller circuit.

[jason123]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

check c57, see what kind of voltage you have.

Fluctuates just like 13.2 v (or standby)

[jason123]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

I would try replacing C14 and see what happens. another suspect might be C5

C5 i tried already. No effect. Just changed out c14 and no effect.

[jason123]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

While you were changing controllers you should have changed your 13v controller. But it may just be bad cap or diode for the controller circuit.

I replaced both ICs... no change

[nomoresonys]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

it does seem like the same issue DXseeker had, I think it's a backlight problem.

[jason123]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

While you were changing controllers you should have changed your 13v controller. But it may just be bad cap or diode for the controller circuit.

it does seem like the same issue DXseeker had, I think it's a backlight problem.

Replaced backlight already, and backlight works with the replacement power supply board.

[captainKKK]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

Seems your issue maybe under the silver heat sink.

[R_J]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

C5 i tried already. No effect. Just changed out c14 and no effect.

What voltage do you have across C5? is it also fluctuating in standby mode?
What is the main filter (C2/C3) voltage? does the pfc turn off in standby and back on when powered on?