LG 50PG20D No picture but has sound, almost fixed but one last question

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Hi all, I have one last question on the repair of my TV but first a little about what I have done.
My Plasma tv was working fine and is only 3 years old and a couple of nights ago the screen went blank but the sound remained, it took my 20 seconds to realize that it wasnt good, remote worked just a black screen and completely black.
I pulled the back of and started to look for obvious problems, I couldn't find or see any so I tested the power supply voltage and all good, all fuses when good, no loose connectors or anything so I did some net surfing and reading here. After that I pulled of the Ysus board and tested all the transistors/fets and all tested fine, had a look over the buffer boards and also all looked fine but im not sure how to test those. I the when to the Z sus board and found 2 shorted IRGP408 transistors, everything else seams fine so I went out to our local TV repair guys to see if they had stock and they didnt, the first told me that would be the problem for sure and the second told me I would need to replace all the boards as it very uncommon for just one to go, they said if the y sus was working I should see something on the display.
So my question is is it common for all the boards to die at once, I had trouble finding another topic where this had happened or do I just take a shot at ordering an $80 board. To replace all the boards it would be around $300 and with a panel that is 3 years old and only HD im not sure its worth it. Any suggestions would be great, I will put up a pic of the inside of my TV.

Thanks Jared

[tom66]

Re: LG 50PG20D No picture but has sound, almost fixed but one last question

In general with a bad Z-sustain you'll get a poor picture but enough to see the Y-sustain is working. However, it is possible that the Z-sustain is overloading the power supply; so try unplugging the power connector and seeing if it shows a dim/blurry picture.

[harts]

Re: LG 50PG20D No picture but has sound, almost fixed but one last question

Ok I gave that a go and still nothing at all

[tom66]

Re: LG 50PG20D No picture but has sound, almost fixed but one last question

Even in a dark room, no glow from the screen? Did you turn the TV off before unplugging it?

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Re: LG 50PG20D No picture but has sound, almost fixed but one last question

yeah nothing at all, I had the power off while connecting and dis connecting, im scare of the voltage that lives in there
The fisrt 2 times I turned it off and on after it died and before I pulled it apart there was a slight glow for a second or so when it was turned back on. Im thinking all boards may be bad or even the panel may have died.

[tom66]

Re: LG 50PG20D No picture but has sound, almost fixed but one last question

Okay, do you have a digital multimeter?

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Re: LG 50PG20D No picture but has sound, almost fixed but one last question

yeah sure do, If it helps to know I have a little knowledge with electronics at the circuit board level also, I can diagnose faulty transistors and a few other components. I also repair pinball machines for a bit of fun, there a better mix of electronic and mechanics though

[tom66]

Re: LG 50PG20D No picture but has sound, almost fixed but one last question

OK, so can you test the Vs voltage? There should be a place marked "Vs_TP" on the power board, or you can test on the pin connector itself. Careful it is around 200V.

[harts]

Re: LG 50PG20D No picture but has sound, almost fixed but one last question

I did test the power supply Vs and Va and they where at 60v and 194v but that was on the power supply side of things, I will test and see it its getting to the sus boards, thanks for the advice its been great!!

[harts]

Re: LG 50PG20D No picture but has sound, almost fixed but one last question

My Y sus has a spot that looks like another connector for the power supply should be mounted there right beside the actual power connector, I tested continuity between the connector and the blank and they are connected in parallel so when the tv is on vs is 194 and va is 60 as per specs on the panel, 5v is also good. I didnt plug the z sus back in as i have removed the components but tested the pins and all are good.

[tom66]

Re: LG 50PG20D No picture but has sound, almost fixed but one last question

That sounds good, my guess would be a control board issue as it is responsible for driving the Y sustain and Z sustain boards and if it went wrong it could have caused the Z sustain to damage itself. I don't suppose you've got a scope?

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Re: LG 50PG20D No picture but has sound, almost fixed but one last question

No I dont have a scope but I have access to one, im not sure that its a very good one though. What would I be testing on the control board?

[tom66]

Re: LG 50PG20D No picture but has sound, almost fixed but one last question

No I dont have a scope but I have access to one, im not sure that its a very good one though. What would I be testing on the control board?

You would need to test that drive signals (that would go to the sustains) are being generated by the control boar. If they aren't I would suggest the control board is at fault.

[harts]

Re: LG 50PG20D No picture but has sound, almost fixed but one last question

Cool, I guess if I find a service manual it will tell me the volts and the frequency im looking for. I will find out the specs of the scope my boss has and give it a look. Thanks again