vertical lines in a Toshiba TV

[vol.2]

Originally Posted by Username1

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Good Evening....

I would hope you could see the line pattern on the scope while syncing off the horiz.
pulse from wherever you wanted to pick it off.... And I can see your thoughts that
if you don't see it there, then you may think it's not in the video...
If that's the case, you should be able to still sync off horiz, and see the noise
on any of the power supply lines you want to look at.... Syncing off the
horiz would just make it stable.... I also agree 100% with your
estimate at the harmonic frequency..... You know what I mean - most
scopes have an external sync input, good in this case to be sure there
is a pulse large enough to trigger on.

If it don't have ext. sync, you could always put channel 2 on horiz, and
sync of channel 2, use 1 to find the noise.


As for the opto-isolator you should be able to take that out, pick another source
select and do whatever to get a blank white screen.... Or just remove it -

So if you feed this tv a signal from an rf modulator with no signal, or if you feed it a
signal from a dot generator with no or minimum dots, no lines, or color bars just
as blank as it can be, do you still see the vertical lines? same , or effected in
any way...? - I mean something blank, but with a sync pulse in it.... no color.

The one thing I disagree with it that for us to see that lines on the screen they
have to come from somewhere.... That scope picture you posted right under the
line " On the left side of L521, it looks fine, but on the other side of L521 it has
this 40Vpkpk 60Hz waveform. I guess it's the raster. It's probably normal, but
I haven't looked at that many different cathode voltages in my life. "

Where your cursor identifies a frequency of 60hz, those vertical tight lines - that
must be what is appearing on the screen - isn't it? Yah, each of those tight
lines is the individual scan lines and you can see they are of irregular height,
should they not be all equal for a white blank screen?

I guess you also have to be careful which ground you pick....? So if your scope
is completely floating.... Like battery power, what do you see if you look at
the ground.... Like hook your ground up to one ground, & scope the other,
and then switch it around....? Anything interesting?

Does it look like anyone might have removed shielding from anything?

And you see what Zeno said about that IC - it's got a few isolated circuits
within it..... Not all on a single Pringles chip.... Several GND's
Several VCC's.....


Good Night....


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Thanks for the thoughts here. I did once capture the collectors of the cathodes while syncing off the HOR pulse and I didn't see anything obvious there.

As an experiment, I also once put .082uf caps between the collectors of the video output and ground. I was given this experiment by someone to check for the banding in the video as the theory being that placing these caps across the video output should kill all AC components and the banding with it.

The banding in that case became lighter, but it was still there.

The conclusion of this experiment was that the banding must not be in the video, or is not fully in the video, and that it must be coupled some other way.

Currently a proposed idea is that it may be magnetic interference from the flyback itself and that I should pull out the flyback and extend the leads in order to move it around and see if that changes anything.

Do you agree that the caps across the video output collectors should have killed the banding if it was wholly present in the video?