LG 42PC1D no image, Hybrid changed

[brogdan]

hello

i also have a problem with a LG 42PC1D
it came with blown fuse and shorted hybrid on ysus

i changed the hybrid and the fuse, all power supply voltages are ok, but still no image.
do you have any ideea?
\i saw that on the mainboard(digital) there are some LEDs: L300 is off and L500-503 are on

[tom66]

Re: LG 42PC1D no image, Hybrid changed

Are Vs, Va, Vsc, and -Vy voltages OK?

[brogdan]

Re: LG 42PC1D no image, Hybrid changed

Vs:184v ; Va:60V; Vsc:26v; -Vy: -150v

[Alastair E]

Re: LG 42PC1D no image, Hybrid changed

VSc doesnt look right to me.....

Have you a Scope?

You could check both panel drive waveforms with the scope....

X-Sus will have a square-wave and Y-SUS that ramp wave if all is OK....

[brogdan]

Re: LG 42PC1D no image, Hybrid changed

now i see.... on the label it says Vsc:120 ans Vy:-200

why are mine so low? i cannot adjust
that much...

[brogdan]

Re: LG 42PC1D no image, Hybrid changed

unfortunately i don't have a scope

[Alastair E]

Re: LG 42PC1D no image, Hybrid changed

So--OK, But your VSc is only 20V but should be 120?

Problem with the VSc inverter board or short on the VSc line.

Disconnect the Buffer Boards from the Y-SUS, Does voltage check at 120V then?

[tom66]

Re: LG 42PC1D no image, Hybrid changed

Low Vsc indicates buffer board short or PASS FET short.

[Alastair E]

Re: LG 42PC1D no image, Hybrid changed

10-1 Buffer-board, Not had a Pass fet fail on a PC1DA--Yet!

Usually just the YPPD-J018C on X-SUS, and the odd buffer-boards....

[brogdan]

Re: LG 42PC1D no image, Hybrid changed

just disconnected the buffer board, and still the same low voltages...i'll check the Vsc and Vy boards, because they are both too low

[Alastair E]

Re: LG 42PC1D no image, Hybrid changed

I would first check those FETS on the two heatsinks--These if short will drag down those supplies from the two inverter boards.

Looks like it may be a Pass fet gone in this one....

[brogdan]

Re: LG 42PC1D no image, Hybrid changed

do you mean the ones marked in red in the picture? they are ok!

[brogdan]

Re: LG 42PC1D no image, Hybrid changed

Sorry

just did a bad measurement!

i have now 120V and -200 as written on pannel

BUT still no image

[Alastair E]

Re: LG 42PC1D no image, Hybrid changed

Does the panel initialise? Is there (In a Dark Room) a faint glow from panel when turned on?

IF all the voltages are correct, and no-glow from panel, then maybe there's a control-board fault or the IPM you fitted is no good, the panel itself is bad, or another fault on Y-SUS

Really need a scope to check the drive waveforms....