LG 50pj350 plasma not powering going to standby

[cequil32]

Recently bought a 50pj350 on Craigslist and trying to make it work. This is my first plasma repair, been pretty successful with LCD but this seems to be giving me some trouble.

After reading on here about others I found one of the 22 ohm resistors on the power supply open and replaced. However, when I connect ysus board I get no output. Disconnected I get the expected voltages.

Any help with the ysus and zsus boards to know if they are bad? I did see a spark on the lower y driver when I was messing with some ribbon cables.

[tom66]

Re: LG 50pj350 plasma not powering going to standby

If you were messing with the ribbon cables while the set is live, you probably damaged the buffers. But you should be careful as there is over 200V on the sustain board at several amps.

[Techstar]

Re: LG 50pj350 plasma not powering going to standby

You must change both of the 22ohm resistors even if only one of them is open, use 7 watt types. Should you only change 1 of them the other often fails after a few weeks or months. The reason they fail is as the screen ages
it draws more currrent through the resistors. Just thought i would mention it.

[cequil32]

Re: LG 50pj350 plasma not powering going to standby

I think i was impatient and didnt let the caps go down before i messed with the cables.

[cequil32]

Re: LG 50pj350 plasma not powering going to standby

I will keep that in mind and replace the other 22 ohm as well.

[cequil32]

Re: LG 50pj350 plasma not powering going to standby

If i follow the training manual and have nothing on the power supply i get the expected vlltages but as soon as i plug the ysus board in there are no voltages and it goes into standby.

[tom66]

Re: LG 50pj350 plasma not powering going to standby

Can you check the resistance between Vs and GND on the Y-sustain?

[cequil32]

Re: LG 50pj350 plasma not powering going to standby

470 ohms between vs and ground

[tom66]

Re: LG 50pj350 plasma not powering going to standby

That is too low. Try powering the TV up with just one or the other buffer.

[cequil32]

Re: LG 50pj350 plasma not powering going to standby

470 was with both y buffer boards removed.

[tom66]

Re: LG 50pj350 plasma not powering going to standby

Sorry, misunderstanding, please connect everything except the two buffers and power TV up, and see if it still goes back to standby.

[cequil32]

Re: LG 50pj350 plasma not powering going to standby

Sorry, misunderstanding, please connect everything except the two buffers and power TV up, and see if it still goes back to standby.

Yes goes to standby

[tom66]

Re: LG 50pj350 plasma not powering going to standby

OK, now try it without the Y-sustain; if that fails then try the Z-sustain (board opposite Y-sustain)

[cequil32]

Re: LG 50pj350 plasma not powering going to standby

With all other boards connected only the ysus board disconnected in the tip left the power supply stays on.

[tom66]

Re: LG 50pj350 plasma not powering going to standby

OK, so the fault is with the Y-sustain.

Do you know how to test the MOSFETs and IGBTs on it? One may be shorted, causing the problem. If you don't know how ask me and we can guide you through, but we need pictures of the board. You can also replace the whole board. Look for the part code, usually begins with EAX.

[cequil32]

Re: LG 50pj350 plasma not powering going to standby

Do you need to take them out of the board to test?

[cequil32]

Re: LG 50pj350 plasma not powering going to standby

I ordered a ysus and both buffer boards. should i order the zsus and buffer as well?

[tom66]

Re: LG 50pj350 plasma not powering going to standby

A ysus failing cannot possibly damage the zsus, as far as I am aware.
There is no such thing as a zsus buffer.

[cequil32]

Re: LG 50pj350 plasma not powering going to standby

The zsus looked like two parts and some on ebay were only selling one board, the bigger. that is why i assumed there was a buffer board.

[tom66]

Re: LG 50pj350 plasma not powering going to standby

There is sometimes an extension board but it usually has no components on it, maybe a single capacitor, but its only purpose is EMI, i.e. reducing radio interference, it doesn't affect the performance of the display itself. The extension board is basically the same as a wire.