LG 50PA5500 No picture. Has sound.

[tom66]

Re: LG 50PA5500 No picture. Has sound.

Your Vsc is too high. Should be 150V.
Pull your upper buffer. If the picture comes back with it out you probably have a bad plasma panel. There is a design flaw on these panels. The side plastic of the case eats into the ribbons of the panel, eventually this kills the buffer board. I had a 50" PA650T with this fault.

[tart9975]

Re: LG 50PA5500 No picture. Has sound.

Thanks for the quick reply Tom66.

I feel like an absolute moron, the Vsc is 178.7 mV and not V.

I went ahead and pulled out the buffer boards.
- With the upper board removed and the lower one in place, the Vsc increases to 60.7 V.
- With both the buffer boards removed, the Vsc is 105.7 V.
All other voltages remain the same.

So should I get a new Ysus board or both the board and buffers?

[tom66]

Re: LG 50PA5500 No picture. Has sound.

You should try these tests (test 1 you can do with a meter, test 2 requires a current-limited PSU):
https://www.youtube.com/watch?v=51SZsfH60EY
https://www.youtube.com/watch?v=Iw0_wFwbij4

If you find a bad buffer replace the buffer and the Y-sustain.

Check the top and middle most ribbons for tears/damage too.

[tart9975]

Re: LG 50PA5500 No picture. Has sound.

One of the ICs on the Upper Buffer tested for short on multiple pins. The lower buffer seems fine.
There was no visible damage to the panel ribbons.
I will order the parts and update on how it goes. Thanks a lot for the help.

[tom66]

Re: LG 50PA5500 No picture. Has sound.

Was it the top most IC?

[tart9975]

Re: LG 50PA5500 No picture. Has sound.

Yes, it was! The top most IC on the Upper Y Buffer tested for short.

Vy = 191 V
Vs = 153 V
VzB = 149.9 V

I got the parts today and installed a new Ysus and Y Buffers. The attached pictures might help to understand how the screen is behaving now. The pictures are when I short the test pattern slot.

[tart9975]

Re: LG 50PA5500 No picture. Has sound.

Update: The top most IC on the New Upper Y Buffer board went dead and is now testing for short.

[tom66]

Re: LG 50PA5500 No picture. Has sound.

You have a bad plasma panel . Sorry, but if you check that IC you will find it has shorted in nearly the exact same place. You can see the lines on the panel where the ribbon is bad. If you then check the panel ribbons you will find a slight tear in the top most ribbon, it's very hard to see but it will be there. Virtually unrepairable unfortunately.

This is caused by the "razor thin" frame screws eating into the panel ribbons due to case expansion/contraction.

I had an LG 50PA650T like this that I had to scrap for the same issue, top buffer board IC blown too.

4th LG "PA" series on here with unrepairable panel fault.

[tart9975]

Re: LG 50PA5500 No picture. Has sound.

I feared that as well.

Thanks for the quick responses and I am very glad I went through this exercise. I learnt a lot.

Thanks folks!

[Measuray]

Re: LG 50PA5500 No picture. Has sound.

just fixed a 50PA5500-UG with the same image. It's the Z-sustain board that causes this image.