RE: Weird distorted shapes

>Look at this screen shot of another builders results...
>https://www.dropbox.com/s/owa3vq5l6f0lgv2/100_3343_zps3521fb63.jpg
>
>Notice the blue is perfectly formed, but the green is all messed up

That looks to me as though the green channel amp is slow to turn on. The
vectors look pretty straight-- they're just either 'fading in' (or 'fading
out' depending on the direction of the draw I suppose) before reaching the
end of the line. Could be a tube issue as well. Looking at the green color
output vs. a deflection channel (or two) would probably show the problem on
a scope.

There might be a little high frequency 'jitter' in there somewhere that's
causing the hash on some of the green verticals. Hard to tell with a
picture-- really need video there. Also could just be that the shadow
mask/dot pitch on the tube is pretty big and sometimes the green verticals
are straddling the mask and appearing on one side or the other.

For Joel's original problem, I would probably try to trace things through
the deflection section with the scope-- put the Star Wars boardset X output
on one channel and then follow X through the deflection section with the
other channel. Set the volts/div to try to keep the waveforms about the
same vertical size on the scope and compare them visually. You should be
able to see that amount of difference/distortion on the screen so you should
be able to see when it appears in the deflection board. (Hard to debug
without knowing the design, but I'm assuming there's probably some sort of
pre-amp that you could look at before it gets to a power-amp stage.)

It does kinda look like its more prominent on short vectors which is
probably a clue. To be more useful I'd want to see the schematic for the
deflection section and/or the layout. Curvey/distorted things like that
could be related to opamp speeds or outputs getting too close to the rails
or L/C or maybe power...

-Clay

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Received on Tue Mar 4 13:46:41 2014