LG TV sound no picture, boards replaced

[voltman]

Would greatly appreciate any help with my LG flat screen TV

LG 43UJ6200UA.CUSYLH Sound no picture. Flashlight test shows picture. Replaced power/LED driver board and main board. Same thing, sound, no picture. Six pin connection from power supply board to LED's shows .02 volts and .03 volts connected, and .02 volts and .03 volts with LED leads disconnected.

If LED's are blown, shouldn't new power boards LED connections have power with LED leads disconnected? Does this power/driver board not put out voltage to the LED's unless there is a draw? No support from new boards provider.

At the 14 pin connector on the power board, I have 11.8 volts at the five + marked connections when the TV is on standby. When the TV is "on" I have 3.45V at the PO connection, and 3.22V at the PDIM, and INVON connections. Wires and connectors between power and main board are good. I have not checked the LED strips yet. Trying to avoid removing screen to do so.

This TV only has one power board and one main board. There is no separate inverter/LED driver board or TCON board.

Thank you for any help or guidance

[neilc6]

Re: LG TV sound no picture, boards replaced

Most novices want to replace the power supply board when there is no backlight or if they flash or flicker. Always confirm the backlights are good by watching them power up with the panel removed or with a led tester before suspecting the ps. Backlights shutting down is a protection feature and not a failure. If they fail open, there will be no flash.

https://www.badcaps.net/forum/showthread.php?t=79561

[budm]

Re: LG TV sound no picture, boards replaced

Lest see good clear pictures of the whole backside of the TV showing all the board, and then good clear straight shots of the whole top and bottom side of the power supply/LED driver board.

[CapLeaker]

Re: LG TV sound no picture, boards replaced

sounds maybe something is fishy with that replacement PSU's backlight driver part. Not convinced on that. There should be power ramping up on the LED connector when you turn the TV on, then voltage should ramp down again. Do the backlights turn on for a second then go out? LED's are current controlled, not voltage controlled.

[nomoresonys]

Re: LG TV sound no picture, boards replaced

Do the backlights come on with cable from powerboard to mainboard unhooked? Power cord should be unplugged before removing cable then plug power cord back in to powerboard.

[voltman]

Re: LG TV sound no picture, boards replaced

"Do the backlights turn on for a second then go out"?

"Do the backlights come on with cable from powerboard to mainboard unhooked"?


When you turn TV on, screen flashes "LG" for a split second then nothing (but sound). When you disconnect cable from power board to main board the TV appears not to get any power. The standby light does not come on and no sound.

I think I will have to check the LED strips. Is there a tutorial on proper screen removal? Advice appreciated, I have never done this before. 43" screen, do I need suction cups, or is there another way? Thanks everyone for your help and super fast response!

[neilc6]

Re: LG TV sound no picture, boards replaced

Disconnecting the cable between the power supply and main board is a test for Samsung TVs. Don't think LG's have pullups so doesn't apply.

43" screen isn't that bad for handling since not super big but you need to be careful. You can turn on the TV with the panel disconnected so you can observe the LEDs flash to identify bad strips but best to do a full replacement with new strips and never run the backlight at max.

Not your exact model but close. https://youtu.be/T2FboV-1PJg

[nomoresonys]

Re: LG TV sound no picture, boards replaced

Disconnecting the cable between the power supply and main board is a test for Samsung TVs. Don't think LG's have pullups so doesn't apply.

43" screen isn't that bad for handling since not super big but you need to be careful. You can turn on the TV with the panel disconnected so you can observe the LEDs flash to identify bad strips but best to do a full replacement with new strips and never run the backlight at max.

Not your exact model but close. https://youtu.be/T2FboV-1PJg

It works for lots of newer tvs, not just samsung, this paticular model might not have them but many tvs these days have pullups.

[budm]

Re: LG TV sound no picture, boards replaced

So where are the pictures I request? Are you really going to take the panel apart without doing more Voltage testing?

[voltman]

Re: LG TV sound no picture, boards replaced

I have to find a hosting sight for pics. I have done more voltage testing. I believe I was doing the tests improperly before . When I tested before, I would power the TV "on" then place my VOM meter leads on the connections. This time I have the meter leads on the connection before turning the TV on. My updated results are below:

Sound no picture. Flashlight test shows picture. When TV is turned on, "LG" flashes for a split second, then no picture just sound. Six pin connection from power supply board to LED's shows 19.55V when turned on then quickly drops to .03V. This happens at both LED1 and LED2. With six pin LED connector disconnected, when turned on, shows 15.6V to 26V then quickly drops to .0V the drop happens so fast it is hard to see on the meter.

Does this sound normal if some of the LED's are blown? If it does, I did not know the drop or shut down occurs so fast.

[Michale32086]

Re: LG TV sound no picture, boards replaced

LGs are famous for this.

You have one or more bad LED strips..

It IS repairable, but it's a bear.. The good news, it's only 43" so it's definitely doable..

[budm]

Re: LG TV sound no picture, boards replaced

1) You can upload the pictures here, no need for hosting site.
2) Is this your board? https://www.shopjimmy.com/lg-cov3444...iver-board.htm
3) You have two LED strings, LED1 + (Anode) , LED1 - (Cathode), LED2 +, LED2- each pin of the LED connector is labeled, so your report does not mean much without the pin names.
4) You need to leave black probe on the chassis, keep red probe on each LED pin one at time then turn on the TV to see how high the Voltage jump up too and settle down to, repeat that on the other 3 LED connector pins.

[voltman]

Re: LG TV sound no picture, boards replaced

1)

1) You can upload the pictures here, no need for hosting site.
2) Is this your board? https://www.shopjimmy.com/lg-cov3444...iver-board.htm
3) You have two LED strings, LED1 + (Anode) , LED1 - (Cathode), LED2 +, LED2- each pin of the LED connector is labeled, so your report does not mean much without the pin names.
4) You need to leave black probe on the chassis, keep red probe on each LED pin one at time then turn on the TV to see how high the Voltage jump up too and settle down to, repeat that on the other 3 LED connector pins.

1. Thanks! pics coming shortly
2.Yes. That is my power board
3. LED1+, LED2+ I corrected my posts
4. This is how I did it

Six pin connection from power supply board to LED's shows 20.5V at LED1+ when turned on then quickly drops to .02V and 19.5V at LED2+ when turned on then quickly drops to .03V. With six pin LED connector disconnected at LED1+ when turned on, shows 20.3V then quickly drops to .0V. LED2+ when turned on, shows 15.6V then quickly drops to .0V. The drop happens so fast it is hard to see on the meter.

Do you mean repeat the testing using the negative contacts on the plug instead of a chasis ground?


Thank you budm for your help

[voltman]

Re: LG TV sound no picture, boards replaced

Pics of old board show something burned up. Board is coated with black residue from whatever burned up. You can see top of back panel in circled area where the smoke or residue went up. The 3 capacitors circled were coated with residue but appear normal. I do not know proper way to test them. I only found one component, I dont know what it is on the upper right corner of the board, it is blue in color. Either it burned up or the thing next to it (to my uneducated eyes looks like a transformer?) got really hot as one side of the blue thing is coated in thick black residue. The board at this area (upper right corner) also shows signs of heat and is stained.

The back side of this board shows black residue (from heat?) in the middle, but otherwise looks ok. To be clear both this board and the main board have been replaced. My assistant is taking notes lol

[budm]

Re: LG TV sound no picture, boards replaced

If you look at the Voltage chart printed on the board, the LED power supply is rated at 58Vdc with current capacity of 550mA, but are only getting 20V without LED connector in place, so your readings do not look right.
What DCV do you have when measure right between the two legs of the main filter caps when TV is turned on?

[voltman]

Re: LG TV sound no picture, boards replaced

Please define or show me where or what main filter caps are. I am using a cheap craftsman digital multi meter, I will try to get something better to retest with.

[budm]

Re: LG TV sound no picture, boards replaced

Main filter caps are the long brown caps rated 450VDC laying on the side.
Pictures of the new board? and where did you get the new board from?
You will be working in the deadly side so do not touch anything with your hands.
Do you have tools for soldering works?

[voltman]

Re: LG TV sound no picture, boards replaced

New board came from ShopJimmy, I have soldering tools but if board is defective, shopjimmy will and should replace it. Voltage at main filter caps with TV on: 373V each

[budm]

Re: LG TV sound no picture, boards replaced

I re-read your post #10: When TV is turned on, "LG" flashes for a split second. That mean the backlights did flash on?
In your post #13: You did test the on the LED1+ and LED2+; you did leave balck probe on the chassis and Red probe on LED1 +and then turn on the TV, correct? The you did the same on the LED2+, correct? But you did not do two more test on the LED1-, or the LED2 - as requested with black probe still on the chassis.
My post #12: 4) You need to leave black probe on the chassis, keep red probe on each LED pin one at time then turn on the TV to see how high the Voltage jump up too and settle down to, repeat that on the other 3 LED connector pins. 4 tests total.

[voltman]

Re: LG TV sound no picture, boards replaced

Correct and correct. I assume at least some of the LED's must flash or I would not see the "LG" this occurs only for a split second when turning TV on. It is not very bright but again, I can see the "LG" for a split second.

I will test with negative probe on chasis ground and positive probe to LED1- and LED2- turning TV on after probes are in place. Will try to get this tonight if not by morning. Thank you again for all of the help.

Does the 373V at the main filter caps sound normal?