LG 50pv400 Plasma Display issue

[smuddge]

Re: LG 50pv400 Plasma Display issue

vy
vsc
both just show a 1 on my multimeter

tried setting at 200 and at 600 on the multimeter.

just get a 1 at the left hand side of the display on meter when i put red to + and black to - on these places.



vbiaz shows 124.2v

here are the places i took the readings

[tom66]

Re: LG 50pv400 Plasma Display issue

Vzbias seems OK. But, really odd, those readings (for -Vy and Vsc), are you putting red one end, black other of the resistor? Does your meter value flicker or is it always "1"?

[smuddge]

Re: LG 50pv400 Plasma Display issue

it flickers and then stops at 1 everytime
cannot get a value other than 1 each time

[tom66]

Re: LG 50pv400 Plasma Display issue

I do recall someone else having this problem and it turned out to be a multimeter which was picking up on the electrical noise/interference produced by the TV. Does moving the meter and cabling as far as practical from the TV (so you can still probe and measure) make any difference?

[smuddge]

Re: LG 50pv400 Plasma Display issue

no difference by moving.
just tried another multimeter and it gave same results.

the one on zsus vbz reads normal.

the ysus board is really making a loud buzzing sound the more i am testing it. Seems to be coming from the silver heatsink area.

would replacing this board get me any further?

i see them on ebay for about 30$ plus shipping which isn't really all that bad. however i would like to repair this board instead of replacing as it is more of a challenge.

[tom66]

Re: LG 50pv400 Plasma Display issue

Your results are pointing to a bad Y-sustain board.

Repair would probably consist on checking obvious parts. I would start first with the capacitors and the controller IC which will be near a transformer on the Y-sustain, this is used to generate the various voltages. It generates many voltages: -Vy for the panel initialisation and floating ground reference, Vsc for the Y-buffer board, -Vy+10V(typically) for the Y-buffer, and sometimes also a ground-referenced 15V supply for other stuff on the board.

If you want to learn more about the failure, it might be more helpful to buy a working board and compare results. You can then figure out exactly what isn't working for future reference.

[smuddge]

Re: LG 50pv400 Plasma Display issue

ok i will look at ordering a new ysus board and post back after I receive it.
hopefully that is all that is bad at least that way i can get it going again and go from there.

thanks for all the help.
very much appreciated.
as usual this site is full of very very helpful and patient people.
glad i found it.

nothing but good things to say about it.

[smuddge]

Re: LG 50pv400 Plasma Display issue

picked up a new ysus finally.
tested it and i get no display and the tv will not even stay powered up with it in.

When i looked at the OLD ysus board on the backside i noticed a burned spot so clearly the ysus I had was bad but not sure what would make the new one turn off the tv when it is plugged in.

tested the fuse on the new one and it is good.

i don't have enough time with power on to test the vy and vsc as the power goes off to quickly.

on another note when i put in the old board now I do not get a display either so I have no idea what is going on....

i don't want to keep buying boards to test in this so any help would be appreciated.

thanks

[smuddge]

Re: LG 50pv400 Plasma Display issue

little more testing and this is what i have come up with.
anyone can chime in here. don't want to waste too much more money on this if it is not fixable

so decided to test this tv again with both ysus boards I have

lets call the original ysus board ysus1 and the new one ysus 2

ysus 1 with only top buffer hooked up I get top half of screen white.
ysus 2 (supposed to be working) tv will turn on and then off

ysus 1 with only bottom buffer hooked up no display
ysus 2 with only bottom buffer hooked up tv turns on then off

the display only showing white only began after I put in the new ysus board that was supposed to be working.

before i tried it i had the full display on the tv as shown in the first picture of this post.

any ideas or is this just scrap now?

[tom66]

Re: LG 50pv400 Plasma Display issue

It is possible your YSUS2 damaged Y-buffers that were used on YSUS1.

[smuddge]

Re: LG 50pv400 Plasma Display issue

if you think that the panel is still ok i will buy another ysus and bith buffers but just dont want to waste that money ic the panel is the problem

too bad no way to know if there is a problem with ysus before testing it. fuse is good

[tom66]

Re: LG 50pv400 Plasma Display issue

I can't be certain, but I've never heard of such panel failures on these newer TVs.

[smuddge]

Re: LG 50pv400 Plasma Display issue

Ok sorry again for how long this took me to get back to.

I have at this point received a 3rd ysus board that came with a corner broken off. (im not having good luck) There was one trace that was cut so I fixed it but running a small wire from the corner that broke to the other side. (not sure if this is fully functional though)

I order 2 new ybuffers and both were tested working and I have to assume that they do because I now get a picture however this is what it looks like.

Any ideas what could be wrong here if it is another bad ysus board I think i will quit and just sell the working parts as I have spent almost as much as a new tv working on this.

Gotta cut my losses at some point but just wanted to see if anyone had any more ideas.... I was told that plasmas are a real pain in the ass and I am finding this one to be the case.

[smuddge]

Re: LG 50pv400 Plasma Display issue

anyone??

[Alastair E]

Re: LG 50pv400 Plasma Display issue

Well--Looks like the Bottom buffer board has a faulty MOSFET on it causing that moving bar in line with the menu title on top of screen....

Not a huge problem, Remove bottom buffer and check for shorts on its MOSFETS....

I had a LG 50PC1da that did this just last week....

[tom66]

Re: LG 50pv400 Plasma Display issue

These boards don't have FETs on the buffers but the lower board could still be bad

[smuddge]

Re: LG 50pv400 Plasma Display issue

thats what i thought also so i returned the first bottom y buffer and got a second one and it is exactly the same. the original bottom y buffer makes bottom half completely black.

fet?

[AWTVs]

Re: LG 50pv400 Plasma Display issue

Same model 50PV400. I have a standby red light but will not do anything else. One click when it's initially plugged in and light comes on but then nothing else. Pressing power on tv or remote has no effect. Any suggestions?

[smuddge]

Re: LG 50pv400 Plasma Display issue

yours sounds like power supply. measure all voltages to see if they are correct coming out of power supply.
I never got my fully fixed. still in same state as it was when I last posted.

was hoping for more info but never got any.

[AWTVs]

Re: LG 50pv400 Plasma Display issue

Does anyone know if the display of LG 50PV400 can be used to replace broken display on a LG 50PV450?