LG 42pc1d issues

[QuantumCheese]

Hi,

I have an LG plasma model 42pc1d which has issues.
the whole screen is quite dim, the colours are, put simply, wrong and any areas that are dark turn complete black and then take a long time or a very bright picture to 'burn off'.

I have already replaced 9 caps (3300uf 10v) on the main psu board the rest (of the big ones) test OK, the next cheapest thing i belive is a y-sus hybrid on the y-sus board, however all the info i can find on this model/fault is for total black screen with ok audio, whereas i have partial black with ok audio.
and the failure mode for the y-sus appears to be 'with a bang' but in this case the fuses are fine and nothing seems to have visually popped - what do you think?
Cheers.
ps. (i'm new to plasmas but have fixed CRT's for many years)

[tom66]

Re: LG 42pc1d issues

This is a Z-sustain failure; the board opposite the Y-sustain. You will get a dim, purple tinted picture if this is failed. See this post for info on how to diagnose this problem.

As it's an LG, it could be the hybrid. Or the Zbias supply. Or another problem. The hybrid is the most common cause.

I have an LG 42PC1D and I simulated a Z-sustain failure by unplugging the Z-sustain power. I got exactly the same problem you describe, does your TV look a bit like this? (Excuse the camera shake.) Of course, in my case, I deliberately made it fail, but plugging it in fixed the problem immediately.

[QuantumCheese]

Re: LG 42pc1d issues

Hi, thanks for the super quick response.
Yea that looks a little like it. I'll try unplugging mine & see what changes!
I was a little unsure if it was OK to power just bits of it without accidentally blowing up the 'other bits'!

Cheers, dude.

[tom66]

Re: LG 42pc1d issues

Hi, thanks for the super quick response.
Yea that looks a little like it. I'll try unplugging mine & see what changes!
I was a little unsure if it was OK to power just bits of it without accidentally blowing up the 'other bits'!

Cheers, dude.

Most Plasma troubleshooting manuals suggest unplugging boards is okay. Wouldn't unplug the control connectors (small signal cable) without unplugging the power at the same time, as it could cause the board to go a bit crazy (but I've never tried it.)

[QuantumCheese]

Re: LG 42pc1d issues

well, thanks for the info but that would appear to not be it!

looking from rear. there is a board on the right that says z-sus on it. there is a board on the L which says Y drive. this is plugged into a board that look eerily similar to the z-sus board on the other side. don't worry, there is a point!

i unplugged the board marked z-sus and half the screen went off-black (vertial split). the rest of screen stayed on and with same problem.
so i unplugged the power to the "board on the left with no label" - the whole screen goes black.

In the service manual i 'obtained' it shows a board all the way down the left (view from rear) and calls it y-drive. and shows a board on the R called z-sus. it also shows a board on the left plugged into the y-drive without a label - so i'm guessing it has two, one for each half of screen?

In addition to original description it's not all purple in the distortion, the colour look a bit purple, but very solarised. luckily the snooker was on and for a short time you could make out that the table was green but it then deteriorated on the dark bits becoming permanent black. by changing channel to something brighter the screen starts to come back to life.

(apologies for long description, it's really hard to describe!)

I guess my point it though, it's not the z-sus! any more ideas?
(or if it is it's not quite completely broke)

[QuantumCheese]

Re: LG 42pc1d issues

Most Plasma troubleshooting manuals suggest unplugging boards is okay. Wouldn't unplug the control connectors (small signal cable) without unplugging the power at the same time, as it could cause the board to go a bit crazy (but I've never tried it.)

If you can recommend one of these manuals & where to get it from i would appreciate that too - I must have spent a couple of hours trying to find a book on plasma internals today !

[cliff_hootarski]

Re: LG 42pc1d issues

Go to http://elektrotanya.com/?q=keres type in you model. It looks like it's there.

[QuantumCheese]

Re: LG 42pc1d issues

Go to http://elektrotanya.com/?q=keres type in you model. It looks like it's there.

Thanks. the one there's a bit more detailed than the one i had.
plenty of digital schematics, seems to omit the psu's though

Definitely looks like a place worth bookmarking though - Cheers!

[cliff_hootarski]

Re: LG 42pc1d issues

You might also try LG training manual. Show quite a few.

[QuantumCheese]

Re: LG 42pc1d issues

You might also try LG training manual. Show quite a few.

Thanks missed that!

"never be afraid to point out what is to you the bleedin obvious"

[QuantumCheese]

Re: LG 42pc1d issues

if your familiar with the training manual it looks like the symptom described as

"The blue spreads on the screen (Mis-discharge)
and power off in 2 ~ 3 seconds.
If you turn on again, it will be same problem"

though the set doesn't turn itself off it does look a lot like that

[cliff_hootarski]

Re: LG 42pc1d issues

Perhaps if you loaded up some pictures of the tv without the back cover on, we could try to determine which board is the Zsus.

[QuantumCheese]

Re: LG 42pc1d issues

Perhaps if you loaded up some pictures of the tv without the back cover on, we could try to determine which board is the Zsus.

Thanks, I think i've worked out what a z-sus board is now. the rtfm would appear to suggest i look into the 'x board'. i'm just trying to work out how to get to it to test as it's in two parts & all the way along the bottom of the unit, and behind EVERYTHING!

[tom66]

Re: LG 42pc1d issues

No, the problem is most likely your Z-sustain. The Z-bias voltage can fail and sometimes just one of the two sustain fuses (each fuses a different supply, Vs or Va) could be blown.

[pecrie]

Re: LG 42pc1d issues

it could be the x board ,if your picture on the screen ,is all very clear and with the right colours.And then you should have a good picture ,only half of the panel.

Since your screen image is not oke ,I would first investigate ,in the IPM`s.There are 2 of them ,on the Z - sus board and one on the Y - sus board.The board ,you said ,that has no name.

The IPM`s are attached to the big black ( or aluminin) heat sinks.In the training manual ,there probably is a part ,showing how to test the IPM for shorts.

Like Tom66 said ,it is probably the IPM on the Z-board ,which is at fault.But test it ,to be sure

good luck

[cadiman]

Re: LG 42pc1d issues

Boards along the bottom will give you vertical bar or half a screen Left or right side.
(if unplugged).

As said above you most likely need a "z" board.

[QuantumCheese]

Re: LG 42pc1d issues

Thanks all for comments so far,

I *had* ruled out the z board mainly because unplugging it just made half the screen disappear but also because the training manual (albeit for a slightly different LG plasma) had only one 'fault picture' that looked like the fault i'm seeing and it didn't link it to a z-sus fail but instead an x-board. I shouldn't rule out the training manual being wrong i guess as the service manual lists the pin-outs of two connectors on the psu the wrong way round!

I've tested both the (white) fuses on both the boards. there all OK
the Va and Vs voltages are within tolerance (0.5v) of the sticker on the set. also the 19V and the 3.4 and 12 are bang on. I can't find a 15V as the training manual suggests the slipping of which to 14V or lower will cause this issue.

I was hoping it wasn't the 'IPM' as you call it, as there are two of them and there a £40 part - unless anyone out there knows cheaper? I couldn't see anything in the service manual about how to test them and the service manual only really goes to board swapping diagnostic levels anyway.

I will try and upload a picture of a test card on it today

If we go all the way back to the top of this thread and tom66's original suggestion of unplugging the z-sus board (the one on the right with the thick red and blue power feed) - i did and half the screen went black. by his logic it should have made no difference i believe?

[tom66]

Re: LG 42pc1d issues

Do you have a scope & 10X probe?

[QuantumCheese]

Re: LG 42pc1d issues

Some screen shots.

1st one is an Full White test,
2nd standard test card
3rd standard test card on a working monitor for ref
4th an image off the tv of i think a beach.

it does look very purple on the full white now i look at it

tom66 - scope & probe not a problem. if it starts to get serious, i have 2 scopes, 2 sig-gens 5 channels of bench supplies, 2 variacs and a 200w dummy load in my lab

[tom66]

Re: LG 42pc1d issues

Jealous. Only one variac, one bench supply and two scopes .

Set your probe to 10X and make sure probe is 600V rated. Probe the Z-drive FFC output and check if the waveform is present (set scope to 5V/div, 100ms/div.)