LG Plasma 60PV450: No picture but sound, even with both Y-SUS and Z-SUS unplugged

[gpaps]

Hello all,

Newbie here, I have some basic electronic skills but far from advanced.
Fell on this site by reading about what seems many of the same problems with some Plasma TVs.

Read through a lof of very very informative posts here. But didn't find any exact solution to my problem:

My LG Plasma TV 60PV450 suddenly lost picture yesterday, although sound is fine. The screen is completely black, no subtle grey at all as I usually see when the TV first displays when powered on.

I removed the cover panel, and unplugged the Z-sus from the power board, powered it back on, sound works fine.

I then waited and plugged back the Z-sus, then disconnected the Y-sus, powered back on, sound works fine.

I then waited and unplugged the Z-sus, so now both Z-sus and Y-sus are unplugged. Powered back on, sound works fine as well.

Now I am not sure which of the two boards is faulty? Could it be both?

If it's only one board I could probably buy a new one and switch it, but at two boards it comes close to a price that's not really worth it for me.

Parts are harder to find in Canada and shipping/taxes from the US hurts even more.

Any help from you knowledgable folks would be much appreciated!

[dick_barton]

Re: LG Plasma 60PV450: No picture but sound, even with both Y-SUS and Z-SUS unplugged

Post some really clear and sharp photo's and I'm sure help would soon be forthcoming.

[ReeceyBurger123]

Re: LG Plasma 60PV450: No picture but sound, even with both Y-SUS and Z-SUS unplugged

You wont get any image with just the Zsus as the panel needs scan drive from the Ysus to get any light emission from it. Do you have a DMM and know how to use it ? Were going to help you diagnose it so DO NOT just start replacing boards.

[gpaps]

Re: LG Plasma 60PV450: No picture but sound, even with both Y-SUS and Z-SUS unplugged

Thank you I am very grateful.

Yes I have a digital multimeter, I tested the fuses and got readings of 0.1 or 0.2 on them (I think one was 0.18). There seems to be one fuse on the Y-sus board, one on the Z-sus, and 3 on the power supply board and all seem fine.

Aside from that, I am not sure where else to test without causing a problem or shocking myself

[ReeceyBurger123]

Re: LG Plasma 60PV450: No picture but sound, even with both Y-SUS and Z-SUS unplugged

Right put the meter to ground and set it to 600v dc. Now if you look at the back of the Pdp there will be a chart which has a list of set voltages on it. You need to check that chart and probe the test point areas for the listed voltages on the Psu and sustain boards and compare the voltages to the panel. The voltages will be like this for example:

Psu:
Vs-208v
Va-63v

Zsus:
Zbias-96v

Ysus:
-Vy -200v

Only test -Vy/vsc with your meter as others will have very high charge voltages that will be more than the meter can handle.

[gpaps]

Re: LG Plasma 60PV450: No picture but sound, even with both Y-SUS and Z-SUS unplugged

Ok this is the part that's a little more advanced for me, but I'll give it a shot.

The chart says Voltage Setting: 5V / Va: 55 / Vs: 201

Powered the TV, put the black probe on a ground screw, then the red probe on the VA TP point and then the VS TP point, I got pretty much the same: 55v and 200v.

Now, how do I test the power to the Y-sus and Z-sus boards? I do not seem to see any TP points on those.

Thanks

[tom66]

Re: LG Plasma 60PV450: No picture but sound, even with both Y-SUS and Z-SUS unplugged

From my memory on fixing the 60PZ950T I had the Y or Z chains off the other boards.

So if you unplug Z and it chains off Y then the set powers on then the Z is bad.
If you unplug Y you have effectively unplugged both Y and Z so it doesn't help the diagnosis.

It's been a while so I can't remember which way around it works but you probably get the jist.

[gpaps]

Re: LG Plasma 60PV450: No picture but sound, even with both Y-SUS and Z-SUS unplugged

From my memory on fixing the 60PZ950T I had the Y or Z chains off the other boards.

So if you unplug Z and it chains off Y then the set powers on then the Z is bad.
If you unplug Y you have effectively unplugged both Y and Z so it doesn't help the diagnosis.

It's been a while so I can't remember which way around it works but you probably get the jist.

If I understand correctly, because I do have sound with both Y and Z unplugged, there is no way to know which of the two has actually gone bad?

[ReeceyBurger123]

Re: LG Plasma 60PV450: No picture but sound, even with both Y-SUS and Z-SUS unplugged

There is test points you just need to look closely at the boards, normally near the pots to adjust that voltage there will be a TP.

[gpaps]

Re: LG Plasma 60PV450: No picture but sound, even with both Y-SUS and Z-SUS unplugged

OK I seem to have found them, wasn't sure that these were test points, hopefully it's the right ones. See attached photos.

On the Y-sus:
VSC: 150
Vy: -177 (normal to read negative voltage?)

On the Z-sus:
VZB: 11

Guess it's the Z-sus that has a problem? If so, any further testing or should I replace that board? Or is it an easy fix?

PS: All boards are connected.

[ReeceyBurger123]

Re: LG Plasma 60PV450: No picture but sound, even with both Y-SUS and Z-SUS unplugged

As Tom says the Ysus and Zsus use chained energy recovery meaning if the Zsus has an issue it will cause the Ysus not to work properly. As the Zbais is so low the Zsus definitely has a fault on it thw Zbais fets and the ER are in the same track likely meaning that can cause the Ysus not to work either. I would say replacing the Zsus should sort the issue.

[syaoran123]

Re: LG Plasma 60PV450: No picture but sound, even with both Y-SUS and Z-SUS unplugged

Does the t-con board have a green light? If not, its dead

[ReeceyBurger123]

Re: LG Plasma 60PV450: No picture but sound, even with both Y-SUS and Z-SUS unplugged

Tcon does yes.

[syaoran123]

Re: LG Plasma 60PV450: No picture but sound, even with both Y-SUS and Z-SUS unplugged

Tcon does yes.

Are you answering for gpaps?

[gpaps]

Re: LG Plasma 60PV450: No picture but sound, even with both Y-SUS and Z-SUS unplugged

Yes there is a flashing green light on the controller.

[syaoran123]

Re: LG Plasma 60PV450: No picture but sound, even with both Y-SUS and Z-SUS unplugged

controller is working fine then

[gpaps]

Re: LG Plasma 60PV450: No picture but sound, even with both Y-SUS and Z-SUS unplugged

Trying to get the Zsus board out but how do I remove these connectors? Don't want to risk breaking them.

What are they called anyways?

Thank you

[gpaps]

Re: LG Plasma 60PV450: No picture but sound, even with both Y-SUS and Z-SUS unplugged

Never mind, I just pulled

Here are some photos of the back side, I don't see anything wrong, no cracked solder.

Anything else I can quickly test to see what's wrong with the board that it gets only 11v at the VZB test point?

[gpaps]

Re: LG Plasma 60PV450: No picture but sound, even with both Y-SUS and Z-SUS unplugged

Should I be testing the buffer boards? Or is this unrelated to this problem?

My screen is totally black. No grey, no half-picture.

[Pop13]

Re: LG Plasma 60PV450: No picture but sound, even with both Y-SUS and Z-SUS unplugged

Did you ever resolve the issue with your TV?