how to fix plama lg 42pt350 help?

[mattstolte]

need help i cant fix a plasma if my life depended on it. Where should i begin. Tv had red power light on outside, when i press power it just clicks like its trying to turn on. I started unplugging cables and ribbons and still trying but cant get any change

[Hamie]

Re: how to fix plama lg 42pt350 help?

What have you unplugged?
Probably a powersupply issue.

Unplug the y and x main.
Any change?

[tom66]

Re: how to fix plama lg 42pt350 help?

Use a volt meter to check Vs and Va on power board.

[selldoor]

Re: how to fix plama lg 42pt350 help?

Hope you at least know enough to know that the set must be off when plugging
unplugging cables

[mattstolte]

Re: how to fix plama lg 42pt350 help?

Vs and va go up when i press power but then goes right back down

[mattstolte]

Re: how to fix plama lg 42pt350 help?

The power clicks off right when the vs and va go up the power supply clicks off

[tom66]

Re: how to fix plama lg 42pt350 help?

Do Vs and Va rise to normal voltages?
Check the white ceramic resistors near top of PSU - they can sometimes fail on this model

[mattstolte]

Re: how to fix plama lg 42pt350 help?

Tom how do i check them

[tom66]

Re: how to fix plama lg 42pt350 help?

Like any resistor - check they meet printed specifications. I think they are usually 22 ohm or 10 ohm. So they should measure about 22 ohm or 10 ohm.

[mattstolte]

Re: how to fix plama lg 42pt350 help?

Im not sure which ceramic ur talking about, im learning so bare with me, are u talking about the red ones in the top right

[tw2005]

Re: how to fix plama lg 42pt350 help?

Do Vs and Va rise to normal voltages?
Check the white ceramic resistors near top of PSU - they can sometimes fail on this model

[mattstolte]

Re: how to fix plama lg 42pt350 help?

Ok so i unplugged z sus and ysus. And power supply will turn on and stay on with va and vs power voltages at correct readings. So as soon as i plug in zsus it will cut off, and i cant plug ysus in or out direct cause it runs from zsus. So is it bad zsus?

[tom66]

Re: how to fix plama lg 42pt350 help?

That is a possibility, if you remove it, you can check it for shorts. But I am confused, you said you had brief Vs/Va. If it were shorted you could not have that.

[mattstolte]

Re: how to fix plama lg 42pt350 help?

ok so when I have everything propely connected this is what happens when I turn on when everythings connected the va goes up to 350 when its suppose to be 55, then the vs goes up to 130 when its suppose to be 201,
now when I take the connector from the zsus and turn it on the va stays at 55 and the vs stays at 201. so now what?

[tom66]

Re: how to fix plama lg 42pt350 help?

If your Va actually went to 350V, there would be flames coming from the plasma panel module. Is your meter an autoranging meter - if so could you try locking it into the highest DC range (refer to your meter's manual for how to set the range manually.) Some digital meters can over-shoot on rapidly changing voltages especially if they change range.

[mattstolte]

Re: how to fix plama lg 42pt350 help?

ok well regardless though tom it works without any of that hooked up, so when I hook vsus back up then it doesn't work, so what else can I check? but it looks like zsus right?

[tom66]

Re: how to fix plama lg 42pt350 help?

It is a definite possibility. If you remove the board, it can be tested, if you supply good clear photos of the top and bottom sides of the board.

[mattstolte]

Re: how to fix plama lg 42pt350 help?

Tom here is pictures of top and bottom of board and on bottom there is a burnt up spot on solder where the i think it is a transsitor or whstever it is? I dont know how to test them 3 legged things. So i was thinking that was it.

[Alastair E]

Re: how to fix plama lg 42pt350 help?

Board looks fine to me, You need to check the MOSFETS etc for shorts....

[tom66]

Re: how to fix plama lg 42pt350 help?

MOSFETs/IGBTs are the three legged devices on the heatsink marked Qxxx.
Diodes are usually two legged. In some cases there are three legged diodes with two pins tied together on the board, these are marked Dxxx.

For Qxxx, you want to put your meter across all three combinations of pins (both ways, 6 per device) on diode test and look for a reading less than about 30. In all cases, leave the reading to settle for a few seconds. A low reading indicates a possible short which requires investigation - it should ideally be removed to confirm.

For Dxxx just test both ways across it and look for about 300 to 700 one way, open circuit the other way, note a shorted transistor can make a nearby diode look bad. It is very rare for diodes to fail in a plasma TV.