LG 42PT350R clicking on/off

[Fengo]

Hi guys, i have a lg 42pt350r plasma that clicks on and off. Initially it had a purple display. I opened it up and try to determined the fault. Disconnected zsus and ysus boards. Measured voltages and all were correct. Disconnected mains and connected plug from zsus. Was in a hurry i guess, coz i got a spark on Va line. Since then tv just clicks on and off and voltage readings on Va is 109 and Vs 404.
Any help will be greatly appreciated.
Thanks

[tom66]

Re: LG 42PT350R clicking on/off

Va is 109???? Vs 404?????? Check your multimeter battery, and you should be using volt DC not AC.

If you connected Va while the set is running, there is a good chance you have damaged the plasma panel (driver ICs), which would not be repairable without full glass replacement. Cables should never be connected or disconnected while running unless they are part of the low voltage side.

[Fengo]

Re: LG 42PT350R clicking on/off

You correct Tom, i used AC instead of DC. Stupid me...lol!!
Never messed with the wiring while tv was running, did not wait till the caps discharged though.
Tv clicks on, high pitch noise from zsus, then clicks off. Repeats that cycle endlessly.
Problem is with the zsus i guess, just dont know which component.
Desoldered one leg of big fuse from board and psu goes on and stays on.
So problem definitely with zsus. Even changed some mosfets on zsus without any changed.
Fuses all checked okay.
Psu only clicks on and off when zsus connected, no other boards.

[tom66]

Re: LG 42PT350R clicking on/off

With Zsus disconencted panel should have a dim, purple image. Does it?

[Fengo]

Re: LG 42PT350R clicking on/off

Nope, no image at all. Screen is completely dark.

[tom66]

Re: LG 42PT350R clicking on/off

Your Vs and Va match panel sticker?

In the middle of the set there's a small green board which connects to nearly all of the others. Please post a picture of that.

[Fengo]

Re: LG 42PT350R clicking on/off

Pic attached.
Thanks Tom

[tom66]

Re: LG 42PT350R clicking on/off

OK, see attached.

TV must be unplugged:

Two holes marked EXT AUTO GEN: Place a small wire jumper connecting them.

The connector I have highlighted: Unplug it.

Turn TV on (plug it back in.) Do you get test patterns? If NO, check Vs/Va. Do they match panel sticker? If NO, unplug Z-sus (this time with power off.) Power TV on again, do purplish/dim test patterns appear?

[Fengo]

Re: LG 42PT350R clicking on/off

No test patterns at all. When z-sus connected psu clicks on and off, no voltage readings on Va and Vs. Z-sus removed voltage match panel sticker.
Also noticed that when ribbon cable fom z-sus to control board were removed, high pitch sound from z-sus were quiet.
But it still clicks on and off.
Problem with z-sus must be on Vs rail, coz when 250V fuse on z-sus were removed, psu clicks on and stay on.
Power also went to control board, and green led flashes.

[tom66]

Re: LG 42PT350R clicking on/off

I think you have a defective Z-sustain then. But one final check. There is a little connector on the Z-SUB board. The Z-SUB connects to the Z-sus and panel. Where does this cable go -- to the bottom of the plasma display? If so unplug it (power must be off!) Then plug set back in WITH z-sus connected. Do Vs/Va come up? Do NOT reconnect this connector with power applied!!!

[Fengo]

Re: LG 42PT350R clicking on/off

Still dead-end. Just clicks on and off.
Also thought z-sus is defective.
Any idea what usually fail on it?
Thanks

[tom66]

Re: LG 42PT350R clicking on/off

Did that connector go to the bottom of the panel (long green board) or not?

[Fengo]

Re: LG 42PT350R clicking on/off

Yes it does.

[tom66]

Re: LG 42PT350R clicking on/off

OK, at least you have ruled out a plasma panel short. It must be Z-sus then. Common faults are shorted transistors, bad diodes but also the chips which drive the transistors can go bad.

[jose6326]

Re: LG 42PT350R clicking on/off

sounds like simialr problems on the Lg tv i picked up yesterday

only difference is the fuse is blowing on the psu

[tom66]

Re: LG 42PT350R clicking on/off

The problem is completely different unfortunately.

[Fengo]

Re: LG 42PT350R clicking on/off

Thanks a mil for your time Tom.
Will try to troubleshoot the most common problems then.
Parts are not readily available in south africa, so i will have to troubleshoot with what i got.

[jose6326]

Re: LG 42PT350R clicking on/off

The problem is completely different unfortunately.

well hopefully its an easy fix

[steven82]

Re: LG 42PT350R clicking on/off

Hi Tom,

Currently facing same problem with my LG. found the zener diode/ scholtky diode kaput and code is blur..xx14 something. can found at Z and Y sus board...may know the to get this part? need help.

[steven82]

Re: LG 42PT350R clicking on/off

Hi,

Fyi, as per attachement.

thanks.