LG 50PZ550-ua no picture, has sound.

[Jepree]

Hello, im new to this world of TV sets and troubleshooting. I have read though post to diagnose the problem myself but with my limited knowledge im not sure where to go from here.

The Plasma started taking long for the picture to appear, about 5 min sometimes, 10 min sometimes, 15 min sometimes but now the screen does not power on at all but has had sound without the picture. When i turn it off i do hear a loud pop.

- Va and Vs measure as posted on the sticker.
- Tried jumping R51 and R52 with no test signal present on screen.

I was going to buy a Ysus, T-con and Zsus boards on line but wondered if there were any ways of testing them?

Any help is very appreciated and again sorry if i sound like an amateur here

[Hamie]

Re: LG 50PZ550-ua no picture, has sound.

Pictures of the boards will help.

Test voltages vsc, -VY located on y-sustain.
Vzb (z-bias) on the z-sustain.

[Hamie]

Re: LG 50PZ550-ua no picture, has sound.

FYI




There should be test points for these voltages, use the + and - points for your DMM probes.

[Jepree]

Re: LG 50PZ550-ua no picture, has sound.

Thanks for the tips. Here were my numbers.

Va=55.1(55) Vs=201.8(201) Vy=190.2(190) Vsc=150.3(150) Vzb=114.9(115)

I also tried unplugging the ribbon cable for Zsus herd sound plugged it back in and unplugged Ysus herd sound as well.

3 things that concerned me were:

1. Disconnected the ribbon cable from the CONTROL BOARD to the MAIN BOARD jumped R51 ato R52 to try the "Test Pattern" but the screen was still blank.

2. On the Ysus Board the resistor FS203 was reading 0.1 ohms - 0.3 ohms while the other 2 on the POWER SUPPLY BOARD were all 0.000 ohms.

3. Dont know if this is of significance but i tried cycling my HDMI cable to see if all the inputs would give sound and all worked except Input 1.

Sorry if i missed anything but im kind of stuck as to where i should go from here.

[Hamie]

Re: LG 50PZ550-ua no picture, has sound.

Are those voltages permanent or do they drop off after a few seconds?
In a darkened room does the panel glow?
Is the Y-sustain producing a slight humming noise?
Is there an LED blinking on the control board?

[Hamie]

Re: LG 50PZ550-ua no picture, has sound.

Fs203 is a fuse not a resistor.
The reading is normal.

[Jepree]

Re: LG 50PZ550-ua no picture, has sound.

-Voltage is permanent.
-Screen is completely black in a dark room.
-No humming noise from Ysus.
-I do not have a blinking LED on the control board, am I suppose to?
Am I suppose to take my voltage measurement after a rough amout of time after power up?

And haha yes I ment fuse sorry!

[Hamie]

Re: LG 50PZ550-ua no picture, has sound.

P31 here:


Plug it back in, and see where the triangle is.
You should have around 12v on the pin above it.

Do you?

[Jepree]

Re: LG 50PZ550-ua no picture, has sound.

No its actually reading 0 volts. Thats on the very first pin on the ribbon connector above the triangle.

[Hamie]

Re: LG 50PZ550-ua no picture, has sound.

are you getting any voltage from the main board on any of the pins?
you can use the small holes instead of the actual pins.

[Hamie]

Re: LG 50PZ550-ua no picture, has sound.

the first pin might actually be NC.
try the one above it.

[Jepree]

Re: LG 50PZ550-ua no picture, has sound.

Ill try it again when I get home from work but I believe when I tried it was at 8v but ill have to double check.

[Jepree]

Re: LG 50PZ550-ua no picture, has sound.

Hamie first and foremost thanks for being so helpful, youre awesome!

So I tested the a couple pins on the ribbon cable off the Control Board like you asked in the picture. Im getting about 3.3v on average for the majority of pins.
As for the Main Board, is there any good places to check for voltage?

[Hamie]

Re: LG 50PZ550-ua no picture, has sound.

Check D1 on the control board. It's an LED.

You may be able to make it light with your meter in diode mode.

The fact that you have voltages to the control board but no LED suggests that you have a problem with the board.

[Jepree]

Re: LG 50PZ550-ua no picture, has sound.

Yes when I had my DMM in diode mode it did light up the LED. Would that mean the the CTRL Board was slowly failing in which the unit would progressively take longer to power up?

[Jepree]

Re: LG 50PZ550-ua no picture, has sound.

Ordered a new Control Board and will post when installed so hopefully that rectifys the problem. Was scared it was going to be the Main Board which no one seems to stock anywhere!

Thanks again Hamie, will keep you posted. And if there were any other tests I could do please let me know.

[Alastair E]

Re: LG 50PZ550-ua no picture, has sound.

Hmm--Is there 12V coming from the PSU?

Wouldn't have been so eager to order a Control-Board myself without a whole load more testing....

Only ever had one faulty Plasma control-board--and That one wasnt confirmed either--Set went back to LG, and they fixed it for free!

[Jepree]

Re: LG 50PZ550-ua no picture, has sound.

Hi Alastar. I get excited time and time again so I just jumped on the Control Board, and because it was in stock as well as cheap lol.

Where is a good place for test points on the PSU to check for 12v? Vs and Va were both within limits, I assumed thoes were the test points.

[Jepree]

Re: LG 50PZ550-ua no picture, has sound.

Curious as to where i would be able to get a Main Board for this unit if needed? Everywhere i look its all sold out or out of stock. Is there a comparable board from another unit i could substitute?

[Jepree]

Re: LG 50PZ550-ua no picture, has sound.

Check D1 on the control board. It's an LED.

You may be able to make it light with your meter in diode mode.

The fact that you have voltages to the control board but no LED suggests that you have a problem with the board.

Again thanks for all your knowledge and help HAMIE! After doing more tests and following the service manual you were right it was that board that was faulty. Purchased a new Control/Logic Board and now she works beautifully again. Again thanks much HAMIE all the help and insight was very appreciated!