LG 42" Plasma 42PJ560R - no picture

[abhi1981]

Hi,
I'm from India. I have a LG 42" Plasma tv which is three years old. About a month back , it would start with a black screen. There was sound but no picture. It would behave normally-- no blinking LED, except that there was no picture. It would respond to the remote and I had to turn it off and on from the remote once to get the picture back. This on/off time increased to about half an hour. Once it turned on it would work perfectly until I turned it off from the remote. Now, even after long on/off attempts, there is no picture-- TV still works normally except no picture . The relay clicks normally every time with each on/off cycle. The mains supply is 220V. TV rated power is 100-240V. Sometime back the mains voltage was 270V. Could that be a problem?
I have opened the back cover --- no bulged capacitors or blown fuses.

Please help.

[tom66]

Re: LG 42" Plasma 42PJ560R - no picture

This is likely to be a main board fault.

If you take some pictures of the internal circuit boards in this TV, there is a way for you to run a self test to confirm if the main board is at fault.

[abhi1981]

Re: LG 42" Plasma 42PJ560R - no picture

Attached image

[tom66]

Re: LG 42" Plasma 42PJ560R - no picture

Need a close up of this board. You will need a small piece of bare wire to use as a test jumper.

[abhi1981]

Re: LG 42" Plasma 42PJ560R - no picture

Is this ok??

[tom66]

Re: LG 42" Plasma 42PJ560R - no picture

Perfect.

Power to the TV must be OFF (power cord disconnected.)

Unplug the connector highlighted in red. You will probably have to press the two sides to release it.

Then place a wire jumper across the two holes highlighted in blue.

Plug the TV in again and turn it on. Test patterns should appear, like below:
http://www.youtube.com/watch?v=xgrvR...9BzGSA&index=1

If you see these patterns, then the main board is at fault. (The board you are testing is the control board. The red cable connects to the main board.)

[abhi1981]

Re: LG 42" Plasma 42PJ560R - no picture

No. There are no patterns, just a black screen. The relay clicks when I switch on the mains and press the power button on the remote.

[tom66]

Re: LG 42" Plasma 42PJ560R - no picture

OK, do you have a digital multimeter?

[abhi1981]

Re: LG 42" Plasma 42PJ560R - no picture

Yes, I have this one.

[tom66]

Re: LG 42" Plasma 42PJ560R - no picture

OK, that's perfect. Set it one click left of the "off" position (600V DC).

There's this board in the middle of the TV, this is the power supply:
https://www.badcaps.net/forum/attach...9&d=1375551633

There's a connector on the left, which has points marked VS and VA among others.

You want to put the black probe of your meter, which goes in COM, on part of the metal frame of the TV. The holes for the wall mount bracket are a good place for example.

Then touch your red probe (in Volts/Ohm/mA) to the VS, and then the VA points. Note the reading on each (you only need to measure one VS and one VA.) The sticker at the top left of the plasma panel states what they should measure, it appears to say Vs: 205V and Va: 60V.

[abhi1981]

Re: LG 42" Plasma 42PJ560R - no picture

Vs=203v
va=59v

[tom66]

Re: LG 42" Plasma 42PJ560R - no picture

The power supply is working, then. The voltages are fine.

In a dark room, can you see a slight glow emitted by the screen?

Can you show me how you configured the test pattern jumper?

[abhi1981]

Re: LG 42" Plasma 42PJ560R - no picture

No, the screen is not emitting any glow when seen in the dark. I used a copper wire as a jumper. Please see picture.

Earlier, why did the TV start working after several on/off attempts? I didn't check all the capacitors with a meter, just visually checked for any bulges.

[tom66]

Re: LG 42" Plasma 42PJ560R - no picture

If it was intermittent, as you have said, I would suspect the control board, especially as the test patterns are not working. It may be a good idea to check all connections first, and inspect for obvious cracked solder joints on the Y-sustain and Z-sustain, those are the largest left and right hand boards.

[abhi1981]

Re: LG 42" Plasma 42PJ560R - no picture

OK. I will check all the connections and let you know in a couple of days.

[abhi1981]

Re: LG 42" Plasma 42PJ560R - no picture

I left the set switched on for some time and I noticed that some parts were warm (marked in red) and the other were cold (marked in blue). Only the yellow transformer on the YSUS board was warm (it is getting some current) and all the heat-sinks were cold - does that mean something is wrong in that area of the board ???? Please advise.

[tom66]

Re: LG 42" Plasma 42PJ560R - no picture

If the panel isn't lighting up, it doesn't draw power. This usually means things on the sustain boards won't warm up. The transformer powers some other stuff on the sustain board which does draw power, so it does warm up. You could try using a hair dryer, or freeze spray, to warm up and cool down parts, to see if you can get the TV to work again temporarily.

[abhi1981]

Re: LG 42" Plasma 42PJ560R - no picture

Didn't find any freeze spray, and warming up didn't help either. Please advise what to do next.

[tom66]

Re: LG 42" Plasma 42PJ560R - no picture

Remove the Y-sustain and Z-sustain, and inspect the solder joints around the transistors. See any cracks?

e.g.

[abhi1981]

Re: LG 42" Plasma 42PJ560R - no picture

The solder joints are fine.