Lg Plasma TV problems

[iadrian]

Hello everybody,

I have a problem with my LG plasma TV.

The problem is the TV sometimes turns on, sometimes not. When it doesn`t turn on it makes the "clicking sound".

It also turns off by itself when it works after 30 minutes or so.

I have read many tutorials and troubleshooting about the "clicking problem" and had no success. I have checked EVERY capacitor in the TV, especially on the power board and everything is OK.

I have even changed the power stabilizer on the power source hopping that would solve this problem but no luck.

As a last resort, I have taken my TV to the "TV guy" in my town. He said that the TV Y-board is overheating and that is causing this problems.

After that, I have places a computer fan directly over that board, connected to the power source, the fan fits perfectly but the TV is still broken.

If anyone can help, I would appreciate it.

Thank you,
Adrian

[tom66]

Re: Lg Plasma TV problems

Can you:
a) tell us the model of your TV e.g. 50PK3800
b) post pictures of inside the TV and of each major circuit board, photos should be clear and greater than 1280x1024 resolution.

[iadrian]

Re: Lg Plasma TV problems

1) TV model is: LG 42PC1R-ZH
2) I will post hi res images tomorrow(I can`t open it right now) of every board and the fan modification I made.

Greetings.

[iadrian]

Re: Lg Plasma TV problems

Here are the pictures of the TV boards.

The whole TV:

The power board:

The processor board:

The power stabilizer I changed on the power board:

The Y board(I added the fan):

The Z board:

[tom66]

Re: Lg Plasma TV problems

Your Z board is actually a Y-sus and the Y board (with your added fan) is a Z-sus

OK, here's a connector on the board.

There's a pin marked AC-DET. While the set is operating, measure the voltage on this pin. To do this, set your meter to 20V DC range, put the black probe on a part of the metal frame, and the red probe should touch the metal sheaf around the pin. Connector must be installed and the TV should be working.

If at any point it drops out, this may be your problem.

You may find it convenient to put a long wire in the connector and set the meter up outside the TV and monitor it while watching the screen.

And please also check it while it won't turn on at all.

[iadrian]

Re: Lg Plasma TV problems

I have measured the requested data. There are 13 pins.

Results:

Declared in order:

3.3v | G | 6 | G | G | 5 | 5 | 5 | VS | G | 5 | RL ON| AC Det|

Measured:

4.7v | G | 5.66| G | G | 4.7 | 4.8 | 5.1 | 4.8 | G | 4.7 | 4.8| 4.5|

From this data, I have noticed only a strange reading from 3.3V pin to 4.7V.

Is that maybe the problem?

The AC-DET pin, the last pin, is pretty steady at 4.55V, sometimes it goes to 4.54V or 4.56V but only for a moment.

The problem usually manifests after turning the the ON - OFF. After you shut it down it wound turn on for a while. I have done this now a couple of times, (ON - OFF) and it works now but the AC-DET pin now has 4.4V.

[tom66]

Re: Lg Plasma TV problems

Can you show me what range your multimeter was set to?

[iadrian]

Re: Lg Plasma TV problems

As you said, 20V DC.

Here is the image in real time measurement of the AC-DET pin :

[tom66]

Re: Lg Plasma TV problems

4.5V is good, the set was running with that? What about when it cuts out or when it fails to start?

[iadrian]

Re: Lg Plasma TV problems

Yes, I measured that while the TV is running.

That is the problem, now the TV is not failing, it is still working . I will try to turn it off an on a couple of more times to see if it will fail.

When I turn it off and back on, the AC DET pin has 4.3V and after a while, 4.4 or 4.5.

What about the 3.3V pin? It has 4.7V. That is ok?

[tom66]

Re: Lg Plasma TV problems

The 3.3V isn't right, but since it's so close to the 5V measurement I'm tempted to think it's a misprint -- I've seen this several times before.

[iadrian]

Re: Lg Plasma TV problems

I have turned it off an on for 11 times and it is working! I can`t believe it.
It is usually showing the problem immediately after the first power off.

When I turn it off and back on, the AC DET pin has 4.37V and after a while, 4.4 or 4.5.

I will test it all day and report any new data.

[iadrian]

Re: Lg Plasma TV problems

Correction! It just showed the problem. Back with information.

[iadrian]

Re: Lg Plasma TV problems

After I turned it off it didn`t turned on again. It makes the "clicking sound" and I managed to turn it on again.

Now the AC DET is 4.2V and when the TV is turned off is 4.7V.

When he tried to turn on (clicking sound) the AC DET varied from 4.7V to 1 V.

Now it works again.

Any ideas ?

[tom66]

Re: Lg Plasma TV problems

You would appear to have an AC detect fault then, good, this is usually easily cured.

Can you provide a picture of under these components?

[iadrian]

Re: Lg Plasma TV problems

Yes. In 5 min.

[iadrian]

Re: Lg Plasma TV problems

Here it is:


Except for one suspicious soldier point (maybe it needs to be re-soldered) I see nothing strange.

[tom66]

Re: Lg Plasma TV problems

I don't know how fast Serbian internet is, but please stop adding photos directly to posts. Just attach them. My 1Mbit internet spent a minute loading this page.

Place solder joints across the indicated points, which will inhibit the AC detect feature.

Disadvantage with doing this is the speakers can sometimes make a noise when the set power is unplugged while running. However, aside from this, there appears to be no disadvantage from doing the AC detect mod.

[iadrian]

Re: Lg Plasma TV problems

Sorry, I will attach them in the future. I have a high speed connection at my home (24 Mbit).

You mean to join this pins??? I am a beginner at electronics and I have to ask I always fear for the worst case possible.

Are you sure this exact pins? because the board is upside down.

If I do this, it can`t explode or something ?

[tom66]

Re: Lg Plasma TV problems

I've done this repair before, as have others, but only on different power supply boards in similar LG models. I haven't blown anything up yet, neither have others. However, with any repair comes the risk of failure or damage, and I can't guarantee 100% success.

Yes, you need to bridge the two points I have highlighted with solder. Be VERY careful not to bridge any other two points.

In the new house I am moving into, we will have 80 Mbit internet, so I may not complain so much, but for now I have to put up with the oversold ADSL network.