LG 50PA6500 have sound, no picture

[joecool869]

Tv was in the trunk of my car when i bought it, the previous owner was moving and couldn't take either with him.

He didn't speak English very well but he said that it didn't work. and wasn't going to take it with him.

So i told him i would get rid of it for him.

I got it home and looked at it and the panel looked good so i figured i would see if i could fix it with information i find here.

I plugged it in and nothing no clicks or lights. so being here in Florida i figured possibly a bad power supply.

I removed the rear cover and found the main board disconnected. So i reconnected everything and powered it back up.

I got a click and a red light on the front of the tv,

i pushed the power button the red light went out and flashed twice. about 5 seconds later i got white noise threw the speakers. and the panel black and has no glow.

i have 54v at the VATP and 204v at the VSTP, I tried removing the upper buffer and powering up and the panel still black. The tabs appear to be in good shape having read about them having issues.

I tried disconnecting the main board from the logic board and jumping the logic and nothing on the panel and still black.

i have to get the resistors to try the other jumper testing i had read.

Is there anything else to try to confirm a bad main board before i buy one?

Thank you.

[joecool869]

Re: LG 50PA6500 have sound, no picture

Also i found a sticker on the back of the tv that appears to be an invoice number from a repair shop, so they may have diagnosed it and left the main board unplugged.

But i would like to be able to diagnose it myself.

thanks again.

[Hamie]

Re: LG 50PA6500 have sound, no picture

You need to check vsc, -VY, and z-bias



Vsc and -VY are on the y-sustain.
Zbias on the z-sustain.

They should have test points marked + and - for the corresponding probes for your multimeter. Sometimes they are measured accross a resistor.

Post your results.

[joecool869]

Re: LG 50PA6500 have sound, no picture

Am i measuring voltage with the black probe to the chassis and red to the positive side of the resistor? or measuring voltage across the resistor?

Measuring with the black probe to chassis and red to the positive side of the resistors are

VSC 197 - 202v
VY 253 - 265v
VZB 149v

measuring across the resistor

VSC 0v
VY 57 - 68v
VZB 149v

[Hamie]

Re: LG 50PA6500 have sound, no picture

Ok looks like a faulty y-sus, or maybe the buffers.

Disconnect the buffers and check the voltages again.
Only test accross the resistors.

[joecool869]

Re: LG 50PA6500 have sound, no picture

VS 149v

VY 189v

VZB 149

[joecool869]

Re: LG 50PA6500 have sound, no picture

thats with only the top buffer removed

[Hamie]

Re: LG 50PA6500 have sound, no picture

I take it that matches your panel sticker like in my post above?

[joecool869]

Re: LG 50PA6500 have sound, no picture

the readings with the top buffer removed are now within 1v of the sticker on my panel, correct

[Hamie]

Re: LG 50PA6500 have sound, no picture

the look accurate anyway.
You have a bad buffer board, maybe both, maybe just one.

See if the TV runs with just the top one plugged in. If you get a perfect image on the top half of the screen you have a blown lower buffer IC

[Hamie]

Re: LG 50PA6500 have sound, no picture

With the top buffer removed do you have an image on the lower 50% of the screen?

[joecool869]

Re: LG 50PA6500 have sound, no picture

lower buffer removed panel is black and the readings are
VSC 0v
VY 57 - 68v
VZB 149v

[Hamie]

Re: LG 50PA6500 have sound, no picture

Ok so the top buffer has a shorted buffer IC.

You can check it over if you want?

Uploaded a photo of the top buffer.

[joecool869]

Re: LG 50PA6500 have sound, no picture

Shouldn't the panel do something on the lower half with just the lower buffer connected?

[Hamie]

Re: LG 50PA6500 have sound, no picture

Would depend how the buffers are linked.
Some TVs run with just one buffer, some don't.

If you're voltages are perfect with the lower buffer connected then it would suggest that it's probably ok.

If you can find the service manual it might tell you if the TV can run with just one.

[joecool869]

Re: LG 50PA6500 have sound, no picture

Okay, Thank you Hammie