Lg 42PJ350 no Picture

[tom66]

Re: Lg 42PJ350 no Picture

15V and 15VF are different supplies

15VF is referenced to the Y-sustain output the same ground used by -Vy and Vsc voltages. It is used by gate drivers and to generate 5VF for buffer boards.

[ajshoe]

Re: Lg 42PJ350 no Picture

just to re-cap. LG 42pj350 plasma that turns on - stays on, logic bd has erratic led flashes, all SMPS voltages are good, Vs, Va all good on Ysus & Zsus bds, 15V off of Ysus is @ 18V on turn on then goes to 4.1V, can hear plasma display come on for 2 seconds, NO DISPLAY. I have replaced Buffer bd, Ysus bd (twice), Zsus bd, logic bd, SMPS, absolutely no change in symptoms with any of those bds.
something is telling Ysus bd to turn off 15V. Is this bad panel ????

[tom66]

Re: Lg 42PJ350 no Picture

I doubt anything is telling Ysus to turn off 15V it probably doesn't have an enable...
Most likely cause is a fault on the power rails somewhere, could be an issue with one of the supplies, short on Vsc/-Vy or Z-sustain.
Need to check as many things for shorts.
Maybe use an oscilloscope to check panel waveforms...might give you an idea.

[ajshoe]

Re: Lg 42PJ350 no Picture

I don't give up on many project repairs but this one is done. taking it apart and parting out boards - I know they're all good. done swapping them in & out ! Have 3 Ysus, 2 Zsus, 3 SMPS, 2 Logic, 2 Main bds, 2 buffer bds, orig remote, stand available. Pretty confident the panel is bad. thanks to all for all the suggestions.

[tom66]

Re: Lg 42PJ350 no Picture

Panel isn't bad, you're missing something.
But good luck selling the parts anyway.

[ajshoe]

Re: Lg 42PJ350 no Picture

U may b right but since no schematic or flowchart on what is shutting down Ysus be - got tired of fooling with it. I did get the plasma panel to energize for 3 seconds before the Ysus shutdown.