Another LG 50PG20 power up with sound but no picture

[freavulv]

google continues to lead me here, and I've read through the similar threads I can find. So I join, and rather than hijack someone's thread I thought I should start my own.

This is my boss' TV. (I'm the maint super, pretty good with my hands, but electronics are a little outside my norm.)

TV worked, he moved it to a new location, (upside down in the back seat of his car, if I understand correctly. Now it doesn't work. I was hoping it was something as simple as a loose connection. I checked them and found no loose ones.

It powers up fine (with both remote or button), and either has an all black screen, or dim screen around the edges, and much darker in the center, like concentric squares. (see pic) Sound and channels work as expected. When I push the power button, it turns from red to blue, blink blue, blink blue stays blue. (I think it was only two blinks)

I have checked the VA voltage to the YSUS, it reads 60, and the VS voltage reads 194. I check the upper buffer board (perhaps incorrectly) and it reads 'open' from +5v to Ground (lower board did the same) both boards +5v read 9.4v to chassis ground while powered up.

I have included pictures of just about everything, if I missed anything please let me know and I'll get them asap. I'm pretty good at following directions. I downloaded the tech training manual for this TV from a link here somewhere.

[christo]

Re: Another LG 50PG20 power up with sound but no picture

looks like there is picture or atleast the tv is powering on. Try reseating all the cables on the bufferboard and all cables on the main board.

It looks like there is video just sparkled.

Give me a sec and ill post a link to a thread that might help.

Edit: https://www.badcaps.net/forum/showthread.php?t=18542

[freavulv]

Re: Another LG 50PG20 power up with sound but no picture

Thanks for the quick reply. I have reset all the cables.

The TV goes to black after about 1 second of the screen as shown. (it took me 3 attempts to get that picture) I'll read through that thread tonight, and stop again in the morning.

[freavulv]

Re: Another LG 50PG20 power up with sound but no picture

I double checked the connection but didn't see any change. Any other ideas?

[rccrasher65]

Re: Another LG 50PG20 power up with sound but no picture

check buffer boards for shorts, very common issue for these sets, with sound and no picture. also check VSCH on y sus, could have taken out both. Remove upper buffer board and see if you get half of a screen.

[freavulv]

Re: Another LG 50PG20 power up with sound but no picture

check buffer boards for shorts, very common issue for these sets, with sound and no picture.

How? I checked the+5v terminal to the ground terminal, in the picture above, and it read open. On both upper and lower boards.

also check VSCH on y sus, could have taken out both.

that I will have to check

Remove upper buffer board and see if you get half of a screen.

I did that, and still nothing on the screen at all

[rccrasher65]

Re: Another LG 50PG20 power up with sound but no picture

there is a training manual for this set, for LG techs. Its online at Lg.com I think. It will show you how to test the buffer boards. there are test points on the back of the boards. Its been a long while since I worked on mine. there are also youtube vids to show how to properly test buffer board. Be extremely careful with the ribbon connectors when removing buffers.

[freavulv]

Re: Another LG 50PG20 power up with sound but no picture

Watched a couple you tube videos, I tested the buffer board, from the ground pins to the ribbon cable pins, and there were no shorts.

I think I found the training manual, I will get back to the TV tomorrow.

[freavulv]

Re: Another LG 50PG20 power up with sound but no picture

I can't find any shorts on the buffer boards. My boards are slightly different than the one in the training manual, but doing the diode test results in similar results. Open with the black on the ground, small voltage readings with the red on the ground.

I don't know what VSCH is referenced above, it doesn't appear in the service manual. I checked the fuses on the ysus and they were good.

I'm at a loss here.

[rccrasher65]

Re: Another LG 50PG20 power up with sound but no picture

On the y sus board, the middle black connector, there is a resistor marked VSC measure across the resistor, should get a - reading in the 190v range, make sure you pay attention the + and - points marked next to resistor. reading should match panel label.

[freavulv]

Re: Another LG 50PG20 power up with sound but no picture

Found it. Checked it. TV turned on, it bounced around a bit, then startled on about 0.7 volts. It was never 190.

Replace the Ysus board?

[rccrasher65]

Re: Another LG 50PG20 power up with sound but no picture

Bad y sus then, check under side of board notorius for cold solder joints.

[freavulv]

Re: Another LG 50PG20 power up with sound but no picture

I didn't see any obvious bad joints but they could be under the foam insulation.

I have baked (350* for 8 min) printer processor boards to fix cold solder joints, would that work here? Or would it be better to order as new one. Searspartsdirect was about 130$

[sugar_ray]

Re: Another LG 50PG20 power up with sound but no picture

rccrasher65

Ive got one of these models as well

My symptoms, tv turn on. Just black no picture and no backlight Audio works fine and remote responds because I can turn volume up with remote. I suspect Y-sus as well. Buffers have no shorts.

However, when I check the VSC resistor on the Y sus. I am only getting a reading of 47. Also on VY resistor im only getting the same reading of 47. According to the training manual I should be seeing 195 at the VY and 135 on the VSC. Adjusting the 2 voltage pots does not increase or decrease my voltages. anything else I should be looking at? Or is this enough evidence to say the Y-board is gone??

freavulv: guess you have to ask yourself if $130 is worth saving an outdated plasma tv that only tops out at 720P?? I have seen these boards online (used removed from bad panels or so they say) some of them very over priced in my opinion.

[rccrasher65]

Re: Another LG 50PG20 power up with sound but no picture

Sugar I suspect bad y-sus replace also. For best price Look on Ebay, but must be careful from whom you buy from. Only purchase from someone who offers a good return policy. I have had good results from Ebay. Shop jimmy is also great place if they have them. A little more pricey but they guarantee their boards for 90-180 days.

[rccrasher65]

Re: Another LG 50PG20 power up with sound but no picture

I didn't see any obvious bad joints but they could be under the foam insulation.

I have baked (350* for 8 min) printer processor boards to fix cold solder joints, would that work here? Or would it be better to order as new one. Searspartsdirect was about 130$

You could always try board bad anyways, but I wouldn't reccomend, fastest results to purchase replacement board.

[freavulv]

Re: Another LG 50PG20 power up with sound but no picture

I replaced the ysus board, and I have a picture again. Thank you very much for helping me learn.

Does the old board have any value?

[sugar_ray]

Re: Another LG 50PG20 power up with sound but no picture

I wouldn't think so freavuluv, glad to hear your you got the LG going!! I'm still searching for a decent price for a Y board. Found several but some insane prices for an outdated 720p set

[rccrasher65]

Re: Another LG 50PG20 power up with sound but no picture

Congratulations on your repair, there are places that repair these boards, a little cheaper,just keep an eye out for one. if they are real cheap probably bad! price should be around $100.00