Snowy Vertical bands on 42MF231D/37

[Paul678]

Ok, not only does this unit have "trails" and "ghosting" problems,
but there are also snowy vertical bands that pop up, depending
on the picture:



They are most
noticeable when there is a dark background. These are not
solid lines, but rather snowy multi-colored pixels, in vertical bands.

Would it be safe to assume that because these artifacts are vertical,
that I may have a problem with my X-main LJ41-02758A board? I
checked all the fuses, and the voltages coming from the main power
supply, and all appears good. No noticably bulging caps either.

Also, upon first turning on the TV, the menus take FOREVER to
"fill in". Here you can see the Journey DVD menu, very slowly
filling in, like an RC time constant (it seems like a capacitor or
something is slowly charging.....):



Finally the menu will fill in properly (something that is instantaneous
on a normal TV), and if the menu is returned to later, it will fill in
faster. I'm sure it's normal for a cold TV to be a bit slow at first,
but this is ridiculous! Additionally, there will be a "burn in" image
of the menu titles afterwards....a bit subtle, but definitely there.

There is also an overall unacceptable amount of "snowiness" to the
picture, especially with dark backgrounds, which even shows
during the TV menu screen.

Might I have a problem with my X-main LJ41-02758A board?

Or is this still only a Y sustain board (LJ92-01200A)problem?

Thanks for any advice.....

[tom66]

Re: Snowy Vertical bands on 42MF231D/37

You have a bad Z-sustain (also known as X-main) board. If when turning the TV on, things seem to slowly merge in (almost like a lava lamp, in various spots, and taking from a few seconds to several minutes) it is a problem with the pre-charge part of the Z-sustain board. If you've also got retention, the erase part is faulty, too. As both parts are faulty, it seems likely something common to it has failed.

The Z-sustain's job is two fold. It precharges the pixels, allowing them to change quickly (this is why plasma screens can't quite reach zero brightness, although they are getting better... it's also why they can update so fast.) It also provides the erase pulse, which clears the pixels. If the erase pulse is missing, you will get image retention, because the plasma screen can actually remember the image (it has a small amount of hysteresis caused by deliberately introduced nitrogen), but unlike burn in it's a temporary thing.

[Paul678]

Re: Snowy Vertical bands on 42MF231D/37

Yes, it's very much like a lava lamp! Oozing quite slowly.....

Ok, so do you have any idea where to look at the component
level on this x-main board? For this particular problem?

It's common for the Y buffer boards
to blow out, taking a MOSFET out on the Y sustain....and I've
replaced this shorted MOSFET and both upper and lower buffers,
but I didn't read too much about the x-main going out as well.

Looks like a less frequent problem.

I've seen this as low as $24 on Ebay......think I should just
buy one?

[tom66]

Re: Snowy Vertical bands on 42MF231D/37

Yes, it's very much like a lava lamp! Oozing quite slowly.....

Ok, so do you have any idea where to look at the component
level on this x-main board? For this particular problem?

It's common for the Y buffer boards
to blow out, taking a MOSFET out on the Y sustain....and I've
replaced this shorted MOSFET and both upper and lower buffers,
but I didn't read too much about the x-main going out as well.

Looks like a less frequent problem.

I've seen this as low as $24 on Ebay......think I should just
buy one?

I would just go for replacing the board. Tracing down the fault could be difficult. If you have a picture, the Y-sustain is usually okay.

[Paul678]

Re: Snowy Vertical bands on 42MF231D/37

Ok, here's an update:

Took the x-main out, just to inspect it. All fuses good. All diodes tested good. No shorted
caps, but didn't measure cap values or ESR. Most resistors measured good. No cracks on the board.
Then I reinstalled it, and the main glass barrel fuse blew when I turned it on. Replaced it, but TV
will not turn on when the x-main is hooked up now (blue light on front turns off almost immediately),
and screen stays black except for random patches of dark grey.

So whatever was wrong with it before, has gone completely bad now, which actually makes
the diagnostic easier.

Checked on Ebay:

Lordy, these can be as low as $13, including shipping!

http://www.ebay.com/sch/i.html?_nkw=...item4ab19198dc


Unbelievable, but it's quite a gamble buying from people you don't know.

But at $13, I don't have too much to lose.....

[Scenic]

Re: Snowy Vertical bands on 42MF231D/37

http://www.ebay.com/dsc/i.html?_nkw=...LH_TitleDesc=1

178 instead of 111 results. No cheaper ones though.

Searched for both model numbers + in description. You can search for multiple keywords at once by putting them into brackets, seperated by a comma (see search bar) or exclude specific words by putting a minus in front of it (without a space in between). Asterisks work as placeholders (tit* will find titanic as well as tits *cough*)

[Paul678]

Re: Snowy Vertical bands on 42MF231D/37

Thanks Scenic. Do you agree with Tom66 that the
problems I had earlier were due to the x-main board?

I usually like to get 2nd, 3rd, 4th opinions.....

[Scenic]

Re: Snowy Vertical bands on 42MF231D/37

Sorry.. I don't have any clue about plasmas. I just like to read through all the threads

[Paul678]

Re: Snowy Vertical bands on 42MF231D/37

No prob. I'm new to this stuff too.

Anyone else care to chime in?

[PlainBill]

Re: Snowy Vertical bands on 42MF231D/37

I'd agree, if the voltages are correct, it has to be the X-main. I can't see the logic main doing it.

PlainBill

[Paul678]

Re: Snowy Vertical bands on 42MF231D/37

Thanks for the input, Plain.

I'll let you all know when I get the board in.....

[tom66]

Re: Snowy Vertical bands on 42MF231D/37

Ok, here's an update:

Took the x-main out, just to inspect it. All fuses good. All diodes tested good. No shorted
caps, but didn't measure cap values or ESR. Most resistors measured good. No cracks on the board.
Then I reinstalled it, and the main glass barrel fuse blew when I turned it on. Replaced it, but TV
will not turn on when the x-main is hooked up now (blue light on front turns off almost immediately),
and screen stays black except for random patches of dark grey.

So whatever was wrong with it before, has gone completely bad now, which actually makes
the diagnostic easier.

Same thing happened to me. I was repairing a 42" Samsung plasma with similiar symptoms, but it was worse, as the entire picture had turned into a blocky, slow to update mess. After performing several tests the Z-sustain gave up completely and the power supply started clicking when the Z-sustain was left plugged in, turned out a component on it had shorted (a MOSFET.) Sustain board was cheap, too, only about £15 including shipping.

[Paul678]

Re: Snowy Vertical bands on 42MF231D/37

Both "Vs" pins 10 and 11 were shorted to ground on my X-main, but I only found 2
transistors: Q4001 and Q4000. Neither was shorted.

Did your new x-main fix all the problems completely?

You had previously mentioned that "if you are getting trails, it means the Vsetup or
Vsetdn timings (on the Y-sustain) are wrong." But is it possible
that the X-main's missing "erase pulse" which causes the image retention, is also
causing the "trails" and "ghosting"? That would make logical sense.

I ask because it seems to me that I may have a good Y sustain board
at this point, because I adjusted the hell out of those two pots, and
I was never able to clear the picture up.

Thanks for your input.....

[tom66]

Re: Snowy Vertical bands on 42MF231D/37

You had previously mentioned that "if you are getting trails, it means the Vsetup or
Vsetdn timings (on the Y-sustain) are wrong." But is it possible
that the X-main's missing "erase pulse" which causes the image retention, is also
causing the "trails" and "ghosting"? That would make logical sense.

When I replaced the X-main in the 42" Samsung I had ghosting/trails left over. Before I did this I had almost no picture and after the picture was still watchable, it was just annoying. I adjusted the Y-sustain's Yfr timing until the retention went away, which was just a small turn one way. I suspect the reason for needing this adjustment is the X and Y boards are matched to each other at the factory.

Here is what the image retention looked like: https://www.badcaps.net/forum/attach...7&d=1318440015

[Paul678]

Re: Snowy Vertical bands on 42MF231D/37

Yes, the noise in your picture looks very much like
the two pics I posted earlier.

I just don't want to spend another $13 bucks, just to get
back to where I was before, with trails and ghosting. And
again, I was never able to clean up the picture adjusting
the Y sustain.

I'm getting close to just Ebaying the parts on this unit. Is it
worth the trouble trying to sell the plasma screen alone? I would
think the shipping would be difficult, it being so fragile.

Either that, or I'll buy a tv from someone I know who has a Samsung
HPR4252x/xaa, that uses the same Y sustain and buffer boards,
which has sound but no picture.

I'm hoping he'll take $10-20 for it.......

[tom66]

Re: Snowy Vertical bands on 42MF231D/37

Yes, the noise in your picture looks very much like
the two pics I posted earlier.

I just don't want to spend another $13 bucks, just to get
back to where I was before, with trails and ghosting. And
again, I was never able to clean up the picture adjusting
the Y sustain.

I'm getting close to just Ebaying the parts on this unit. Is it
worth the trouble trying to sell the plasma screen alone? I would
think the shipping would be difficult, it being so fragile.

Either that, or I'll buy a tv from someone I know who has a Samsung
HPR4252x/xaa, that uses the same Y sustain and buffer boards,
which has sound but no picture.

I'm hoping he'll take $10-20 for it.......

No, it's not really worth it. Try and fix it first. I'm 96.4% sure that it's the X main.