Vertical Compression - Videokarma.org TV - Video

johnfull · #1 02-09-2008, 11:18 AM

Has anyone tried retrofitting a set with
switchable vertical compression?
I want to be able to watch the new HDTV signals
on my old 1990 31" ColorTrak2000 model (and
widescreen DVDs also). The set has a wonderful
color gamut and crystal clear focus. When the
converter boxes come along, I'm hoping that
they will offer the same option for picture shape
as DVD players do. That way, I can select 16x9
and watch the finer raster on a compressed picture.
As it is, I have my DVD player set on 4x3 and
have the letterbox scan lines wasted.
I have a newer JVC 32" with compression and
it has excellent pictures. I prefer the colors on
the old RCA, however.
Any thoughts?

andy · #2 02-09-2008, 11:43 AM

If it has a pot for vertical size, it would be as simple as adding a second pot and a switch to change which one is in circuit. You should try to design it so that it doesn't lose vertical deflection when when you switch it. For examplt, if lower resistance = a larger picture, then set it up so that the second pot is connected in parallel to expand the picture for full screen.

Be aware that there may be objectionable stuff visible in the VBI when the picture is compressed. Macrovision and other VBI data will probably show up. TVs with a 16:9 feature have to blank this.

johnfull · #3 02-09-2008, 03:41 PM

Thanks, Andy.
It does, indeed, still use the pots for some
functions. The Bias and Drives and Pin Cushion
and Horizontal Centering and Vert and Horiz
size are still like the good old days.
I think I might experiment with cranking the
pot that's there first to see how it looks before
going further. I'm not really a technician, but I
know some basics. The idea of having additive
resistance is a good one. I hadn't thought of
what would happen in that split second when
there is no signal at all between the two values.
I guess it could fry something to concentrate the
beam at full bore on a single raster line.
The problem I have with the pots is that they
seem frail. After so many years, the Bias and
Drive controls have gotten non-linear. It takes a
lot of patience and even more luck to get an
acceptable setting for those. I would hate to think
that the vertical size is just as frail, but I bet it is.
Thanks again!

freakaftr8 · #4 02-12-2008, 04:50 PM

This is cool and I didn't think of this before, the 66 Magnavox I have sure looks crisp and good when I shrink the vertical size down...

andy · #5 02-12-2008, 04:54 PM

Before TVs commonly had a wide screen mode, videophiles would often use the service menu to reduce the vertical size. The extra scan lines help, but I think the fact that the DVD player doesn't have to scale the wide screen picture makes the most difference in picture quality. Some DVD players do an awful job of compressing the vertical size into a letter box format.

johnfull · #6 02-18-2008, 05:38 AM

Older sets use potentiometers rather than service
menus. My 1990 ColorTrak2000 has many electronic
switches, but Vertical size is one that remains old
fashioned. And the pots wear out quickly from use...

freakaftr8 · #7 02-18-2008, 09:52 AM

Heres my tgought. Solder in a pushbutton switch to the center and the outside post of the pot. on the switch solder in a resistor, test to see which resistor would make sufficent heighth. Then when you push the button, viola, shrunken raster good for digital mock up quality. when the switch is depressed, full heighth. Would this work?

jpdylon · #8 02-18-2008, 09:59 AM

That is completely do-able. The newer sony digital chassis (pre HDTV) have a feature in the menu to enable this.

The vertical compression makes it look very high res.

johnfull · #9 02-18-2008, 12:54 PM

Andy had talked about a second variable
resistor and a switch. I think that would be a lot
more do-able than trying to find the exact value
that makes the right 16x9 proportion. The switch
would add extra resistance to the original one
to enlarge/shrink the picture between 4x3 and
16x9. I'm just not a techie to attempt such a
thing. I use wooden dowels to push on bad
solder joints to keep the darned thing running!
So, I'll wait till HDTV converters are actually on
the market to try one out and see. The quality
of DVDs without compression is just fine, though
with more raster than would be evident with
compression...

Quote:

Originally Posted by freakaftr8

Heres my tgought. Solder in a pushbutton switch to the center and the outside post of the pot. on the switch solder in a resistor, test to see which resistor would make sufficent heighth. Then when you push the button, viola, shrunken raster good for digital mock up quality. when the switch is depressed, full heighth. Would this work?

johnfull · #10 03-01-2008, 10:55 AM

It's great to hear that the converter boxes are
now available. I haven't gotten a coupon as yet,
so I haven't gone to Best Buy to see the gamut.
Has anyone found a letterbox option on any box?
In other words, a way to get anamorphic signal
on a 4x3 that can be compressed to 16x9, as
we have talked about in this thread? Curious...