First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

[johnboy1313]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

Can't see a problem. I would expect the panel to glow with everything it is given...

I wish I knew more about this. Everything I've read says that the output from the boards should have looked odd, due to overworking, if the panel was bad. These boards do not appear to do that.

I've got that Panasonic plasma that I've posted about in another thread. Even when that set would not power on, I could clearly see the panel prime, even in a lighted room. This set does not do anything like that.

I just don't get it.

[tom66]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

Can't see a problem. I would expect the panel to glow with everything it is given...

[johnboy1313]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

From the top right pin. I can't think of anything else but the panel.

[tom66]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

You could call this the digital board. It is essentially the same as a T-con in an LCD TV.

Try scoping that top right pin.

[johnboy1313]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

Back to this one. I've had a few sets on the bench this past week that kept me from parting this one out. I'm still not ready to say the panel is bad. The evidence just doesn't support it. I worked on a Panasonic plasma this week and if anything the buzz emitted from the LG is quieter than the buzz emitted from the working Panasonic panel. I will attempt to get the scope again tonight.

That looks like a factory mod to me.
Top right pin might be the clock.

I assume you are saying I should scope the top right pin. Is this correct? Is this board also called the digital board? In this link, posts 11 and 13, a member going by the name randtek outlines a procedure for testing the digital board.

[tom66]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

That looks like a factory mod to me.
Top right pin might be the clock.

[johnboy1313]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

Sorry it's taken so long. My interest in fixing this has dropped off a bit lately.

[johnboy1313]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.



Here's the control board. I think it's been worked on too.

[tom66]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

Depends -- if you find it, post a picture. I can highlight the oscillator output pin.

[johnboy1313]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

What am I checking it for? How am I checking it?

[tom66]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

Typical appearance (left), bottom of device (right):
http://www.sz-wholesaler.com/userimg...llator-701.jpg

[johnboy1313]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

What's the oscillator look like? I had to bring the scope back this morning do I need to get it again?

[tom66]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

It was directed at both.

The Vsetup ramp is that rising voltage captured on the scope.

All other timings are correct.

As far as I am concerned the control board is sending all the right signals and the Y-sus and Z-sus are properly interpreting them.

Check the oscillator on the control board -- it's usually underneath the main board on this chassis.

[johnboy1313]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

If the logic board has been worked on then that could be the fault. The oscillator is what produces the signal to turn on the panel drivers. If that is not present then you would get the no picture fault. It should output a 100MHz sine wave. If that is not present then that is your problem.

Edit: It looks as though that might be the Main Board but it is hard to tell with out seeing the whole board. Either way I would check the oscillator on the logic board.

Yeah, it's the main board. What's this oscillator look like?

There should still be pre-discharge from the panel if it's getting the Vsetup ramps though. And the Y-sus and Z-sus won't generate the right outputs without correct timing.

Is this directed at me? I haven't any idea what it means. Sorry

[tom66]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

There should still be pre-discharge from the panel if it's getting the Vsetup ramps though. And the Y-sus and Z-sus won't generate the right outputs without correct timing.

[rayrod81]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

If the logic board has been worked on then that could be the fault. The oscillator is what produces the signal to turn on the panel drivers. If that is not present then you would get the no picture fault. It should output a 100MHz sine wave. If that is not present then that is your problem.

Edit: It looks as though that might be the Main Board but it is hard to tell with out seeing the whole board. Either way I would check the oscillator on the logic board.

[tom66]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

3.4V_ON just turns on the 3.4V output, so it's a logic signal around 0V off, 2~5V on.

[johnboy1313]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

Looks like this one has me beat. I'm not going to throw good money after bad in an effort to fix an antique anyhow. So with one last effort to hit it out of the park, I'll post this.



The top pin of connector P800 labeled 3.4V_ON shows 4.75V when on and 0V when off. Does that mean anything to you? I will be parting this one out with the assumption that the panel is bad if I haven't figured anything out by this weekend.

[tom66]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

I can barely here any buzzing, but it's almost always continuous and very loud. All plasmas emit a very slight buzzing in operation.

[johnboy1313]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

I rechecked the regulator on the main board. I either misprobed it or didn't remember it right because it has 5v at the center pin now.

I think it's gotta be the panel. I just unplugged the ysus and powered it on and there is absolutely no buzzing before the speakers come on. Did you watch the video I made? Coul you hear the buzzing?