LG 42PX4RV-TA, Black screen but sound ok

[tom66]

Re: LG 42PX4RV-TA, Black screen but sound ok

OK, do you see the 4 pin connector going to the Y-sustain from the power board? It should have 5V on it.

If you do not have any slight glow from the plasma panel, then there are three possibilities (given heatsinks on boards are getting warm):
- Lack of Y-ramp waveforms for panel initialisation, although, some pixels should still work
- Both Y-buffer faulty
- Broken panel glass in some way or gas has leaked (non repairable)

[reality]

Re: LG 42PX4RV-TA, Black screen but sound ok

I have disconnected both the top and bottom buffers one after the other and the results are as follows;
With top disconnected: screen displays some colored horizontal lines at the top
part of the screen which almost make up some raster
and later began to reduce gradually
With bottom removed : Less such display,

[tom66]

Re: LG 42PX4RV-TA, Black screen but sound ok

Can you show us what the picture is like in each case of unplugged buffer boards?

[reality]

Re: LG 42PX4RV-TA, Black screen but sound ok

I don't know what has gone wrong. I removed each buffers one after the other as i did before but this time , there was no display on the screen anymore as it was when i first did it. I even repeated it to be sure but nothing displayed anymore.

[tom66]

Re: LG 42PX4RV-TA, Black screen but sound ok

Did you isolate the connector going to the buffers, or not? You could have a loose connection too -- check for that.

[reality]

Re: LG 42PX4RV-TA, Black screen but sound ok

I isolated the connectors! I also removed the screws used to connect it to the y-sus. Could that be the problem?

[reality]

Re: LG 42PX4RV-TA, Black screen but sound ok

Please, what more can i do?

[tom66]

Re: LG 42PX4RV-TA, Black screen but sound ok

Do you still have -Vy and Vsc?
There is a board -- the control board -- which connects to the Y-sustain, Z-sustain and other parts... it should have a few LEDs on it, what are they doing? Lighting up, flashing, nothing? Note: this is not the board which has the video inputs on it.

[reality]

Re: LG 42PX4RV-TA, Black screen but sound ok

I don't know but the only board that has LEDs on it is the same that has the video inputs on it and the photo is shown below. The LEDs are lighting up and can be seen inside the wire loop. The -vy and vsc voltages are still the same.

[tom66]

Re: LG 42PX4RV-TA, Black screen but sound ok

The board in question is probably below the main board. Long time since I did one but trace the flat white cables coming out of the Y-sustain and Z-sustain.

[reality]

Re: LG 42PX4RV-TA, Black screen but sound ok

I found a board under the main board. It's shown below. is it the one you are referring to?

[reality]

Re: LG 42PX4RV-TA, Black screen but sound ok

I think it is, there are three green LEDs and there are lighting up.

[tom66]

Re: LG 42PX4RV-TA, Black screen but sound ok

That is the control board. If the LEDs are lit up the board is probably working, unfortunately without a scope, it's hard to tell where the problem is, you would need to check various waveforms to see what is going missing on its way to the plasma screen.

[asjad]

Re: LG 42PX4RV-TA, Black screen but sound ok

lg 42px4rv bad picture but sound is ok