LG 50PA5500 Good sound but picture barely visible

[dckc]

Tv just over I year old failed suddenly, no picture at all. The TV was transported about 200 miles from New jersey to Pennsylvnia and failed about a week after we placed back into service. I had it diagnosed at a repair shop but decided not to fix because of cost. Shop said problem was "Upper Y Drive". I replaced upper Y buffer; still no picture. Next replaced "Ysus" board and now have good sound with complete but barely visible picture. Brightness and contrast controls seem to function but have little effect at improving brightness of picture. Also screen has black speckling that is fixed. (does not change with picture). Any suggestions on where to look next would be appreciated. I attached a picture which is about the brightest I can get with contrast at 100 and brightness at 0. thanks in advance for your help.

[tom66]

Re: LG 50PA5500 Good sound but picture barely visible

This looks like a Z-sustain fault to me. Do you have a digital multimeter?

No idea how any competent shop diagnosed this as an upper Y-buffer fault. It looks completely different.

[dckc]

Re: LG 50PA5500 Good sound but picture barely visible

Thanks Tom66, I do have a digital multi meter. I've also visually inspected that board but see no obvious defects such as bulged caps or burnt resistors.

[tom66]

Re: LG 50PA5500 Good sound but picture barely visible

On the board there will be a component or points marked Vzbias. Please measure across the point indicated by this marking and tell us what you get.

[dckc]

Re: LG 50PA5500 Good sound but picture barely visible

I measured across a resistor marked VZB near the top of the board. I'm getting 136 volts at first check. After about a minute it's reading 148 and seems to be holding there.

[dckc]

Re: LG 50PA5500 Good sound but picture barely visible

On the board there will be a component or points marked Vzbias. Please measure across the point indicated by this marking and tell us what you get.

This is a follow up to my previous post. I could not find a point labeled "Vzbias". I found one marked "VBZ" (across R412) with a voltage of 148 vdc and one marked "zbias" (at pin 8 of connector p101) with a voltage of 2.14 vdc. I attached some pictures of the entire zsus board and close ups of these points. I hope this helps.